Science Analysis Report
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MATISSE Consortium OCA-UNS-CNRS, Nice, France MPIA, Heidelberg, Germany MPIfR, Bonn, Germany NOVA, The Netherlands ITAP, Kiel University, Germany Vienna University, Vienna, Austria li Very Large Telescope MATISSE Science Analysis Report Doc. No.: VLT-TRE-MAT-15860-9008 Issue: 2 Date: 01.03.2012 Author(s): B. Lopez, S. Wolf, W. Jaffe et al.* Name Project Manager: Signature Date Signature Date Signature P. Antonelli Name Principal Investigator: Date B. Lopez Name * The other contributors to this document are: J.-L. Menut, F. Millour, K.-H. Hofmann, A. Matter, O. Chesneau, S. Lagarde, P. Bério, G. Weigelt, J.-U. Pott, J. Hron, M. Hogerheijde, F. Ober, A. Juhasz, , R. G. Pétrov , C. Paladini, A. Chiavassa, L. Mosoni, K. Meisenheimer, M. Vannier. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 2 of 64 CHANGE RECORD ISSUE DATE 1 1 04/10/2010 16/02/2011 SECTION/PAGE AFFECTED All All 2 01/03/2012 All REASON/INITIATION/DOCUMENT/REMARKS First Issue From post-PDR issue to FDR one. The changes involve most sections. The changes aim in particular at improving the descriptions of the requirements derived from the L&M band, motivated by the expected scientific return. The changes aim also in defining the necessary improvements on the VLTI infrastructure in order to boost the science cases. Second Issue MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 3 of 64 TABLE OF CONTENTS 1 SCOPE ............................................................................................................................................................................. 5 2 APPLICABLE DOCUMENTS...................................................................................................................................... 5 3 REFERENCE DOCUMENTS ....................................................................................................................................... 5 4 MAIN INSTRUMENT CHARACTERISTICS ........................................................................................................... 6 4.1 5 MATISSE Performances .......................................................................................................................................... 6 REQUIREMENTS DERIVED FROM SELECTED SCIENCE CASES .................................................................. 8 5.1 Primary Science Case: Star and Planet formation .................................................................................................... 8 5.1.1 NIR/MIR long-baseline interferometric observations of circumstellar disks ................................................... 8 5.1.2 Feasibility studies (I): N band, Continuum..................................................................................................... 10 5.1.3 Feasibility studies (II): L (M) and N bands, Continuum ................................................................................. 24 5.1.4 Feasibility studies (III): L and M band, Lines ................................................................................................ 35 5.2 Primary Science Case: Active Galactic Nuclei ....................................................................................................... 42 5.2.1 Introduction .................................................................................................................................................... 42 5.2.2 Simulation results ........................................................................................................................................... 42 5.2.3 Observability of AGNs with MATISSE ........................................................................................................... 45 5.2.4 Fringe Tracker Requirements ......................................................................................................................... 45 5.2.5 Number of targets versus sensitivity ............................................................................................................... 45 5.3 Secondary Science Case: Evolved Stars ................................................................................................................. 47 5.3.1 Hot stars surrounded by disks ........................................................................................................................ 47 5.3.2 Cool giants and supergiants ........................................................................................................................... 48 5.4 Secondary Science Case: Extrasolar Planets .......................................................................................................... 51 5.5 Secondary Science Case: Solar System Minor Objects .......................................................................................... 54 6 SUMMARY ................................................................................................................................................................... 56 6.1 6.2 7 Science case requirements ...................................................................................................................................... 56 Feasibility of science programs .............................................................................................................................. 57 VLTI INFRASTRUCTURE: THE DESIRED EQUIPMENTS ............................................................................... 58 7.1 7.2 7.3 7.4 7.5 External Fringe tracker ........................................................................................................................................... 58 Tip-Tilt correction with IRIS .................................................................................................................................. 62 Lateral pupil motion monitoring ............................................................................................................................. 62 VLTI data content ................................................................................................................................................... 63 Use of PRIMA with MATISSE .............................................................................................................................. 63 APPENDIX (1): ABBREVIATIONS AND ACRONYMS ................................................................................................ 64 MATISSE Science Analysis Report Doc. Issue Date Page INTENTIONALLY LEFT BLANK VLT-TRE-MAT-15860-9008 1 01.03.2012 4 of 64 MATISSE Science Analysis Report 1 Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 5 of 64 SCOPE The purpose of this document is: To summarize the main instrument characteristics (see also MATISSE Technical Specifications : VLTSPE-ESO-15860-4820 for the detailed specifications), To validate, according to the MATISSE Performance Analysis Report : VLT-SPE-MAT-15860-9007, the feasibility to perform selected science cases To illustrate the potential of the image reconstruction packages, To motivate the desired equipments for the VLTI infrastructure like for instance the second generation fringe tracker. 2 APPLICABLE DOCUMENTS AD Nr Doc Nr AD1 VLT-SPE-ESO-15860-4820 AD2 VLT-ICD-ESO-15000-1826 3 Doc Title Issue Date MATISSE Technical Specifications 1 12.07.2011 Interface Control Document between 6.0 22.06.2009 VLTI and its Instruments (part I) REFERENCE DOCUMENTS RD Doc Nr Nr RD1 VLT-TRE-MAT-15860-4325 RD2 VLT-SPE-MAT-15860-9007 RD3 VLT-TRE-MAT-15860-4336 Doc Title Issue Date MATISSE Phase A Science Cases MATISSE Performance Analysis Report MATISSE Phase A Complement to the Science Case Document. Answer to AI2 1 2 01.06.2007 01.03.2012 1 15.09.2007 1 1 4 01.03.2012 01.03.2012 01.03.2012 and AI3 of the Phase A Board Report, Contribution to the Answer to AI1. RD4 VLT-SPE-MAT-15860-9305 RD5 VLT-TRE-MAT-15860-9304 RD6 VLT-TRE-MAT-15860-9004 Data Reduction Library Design Exposure Time Calculator Instrument Specifications MATISSE Science Analysis Report 4 Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 6 of 64 MAIN INSTRUMENT CHARACTERISTICS MATISSE is a 4-way beam-combiner instrument for the ESO VLTI, designed to be sensitive from the L to the N band. Its main characteristics were defined during the Phase A Science Case analysis [RD1]. The characteristics and performance of MATISSE are specified in the Technical Specification document [AD1]. The performances have been studied in the Performance Analysis Report [RD2]. Main characteristics and capabilities of MATISSE: The number of combined beams is 4. The instrument can operate with 3 or 2 beams. The Sensitivity, sampling, and throughput of MATISSE are optimized for the L and N bands. The L band is specified [AD1] from 3.2 to 3.9 m and N band from 8.0 to 13.0 m. MATISSE will operate also in M band, from 4.5 to 5.0 m. The L, M, and N bands can be observed simultaneously. The instrument must be able to observe with different spectral resolutions. Two spectral resolutions are possible in N band (R ≈ 30, R ≈ 200) and 3 in L&M bands (R ≈ 30, R ≈ 500 for L and M, R ≈ 1000 for L only). The full simultaneous coverage of the L&M bands, in low and medium resolutions, and the full coverage of the L band, in high spectral resolution, require an external fringe tracker [RD2]. MATISSE will measure the coherent flux, visibilities, closure phases and differential phases. Differential visibilities can also be derived. These quantities will be measured as a function of wavelength in the selected spectral resolutions. The specifications on these quantities are given in the Technical Specifications document [AD1]. 4.1 MATISSE Performances In the following section, we present estimates of the signals that MATISSE would measure from several important classes of astronomical targets. Then we will compare the estimates of these quantities with the performance limits expected from MATISSE. These limits have been specified in [RD2]. In the following tables we present performance figures, derived from the material in section 8 of [RD2], for the applications below. The quantities are presented here in less detail than in [RD2]; in some cases “typical” values have been chosen where the specific values depend on the exact configuration, e.g. whether BCD is used or no. Limiting Fluxes for self-tracking: [RD2] Section 8.1 Telescope/Bands L-band M-band N-band 1.9 Jy 5.7 Jy 11.6 Jy AT 0.18 Jy 0.44 Jy 0.7 Jy UT Table 1: Limiting Fluxes for self-tracking MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 7 of 64 1- Uncertainty in correlated flux in 15-min integration These numbers below are derived from Tables 8.2.1, 8.2.2 and 8.3.1 of [RD2] assuming the N-band measurements will be done in HighSens mode and the L-band in SiPhot mode. The row labelled UT (no FT) gives the noise level in 15 minutes for a source which is strong enough to be self-tracked, i.e. stronger than given in the above table. Telescope/Bands L-band M-band N-band 16 mJy 80 mJy 1.0 Jy AT(with FT) 5 mJy 9 mJy 60 mJy UT(no FT) 1.5 mJy 5 mJy 50 mJy UT(with FT) Table 2: Correlated Flux noise per spectral channel and low resolution Absolute Visibility uncertainties The estimates below, in percent, are expressed in the form x / S y . The first term, x/S, represents the contribution from the noise, where S is the flux in Jy. x is estimated for bright sources. The second term is the additional uncertainty due to calibration errors. The two terms should be added in quadrature to arrive at a final estimate. Telescope/Bands L-band M-band N-band AT(with FT) 1.8/S1.6 8/S1.1 160/S1 UT(no FT) 0.6/S2.3 0.8/S1.5 9/S2.8 UT(with FT) 0.3/S2.5 0.5/S1.7 9/S1.1 Table 3: Visibility errors (%) in SiPhot mode Differential Visibility uncertainties For differences in visibility over wavelength within one band the following apply: Again the estimates are in the form x / S y with S in Jy. The noise contributions are the same as in the Absolute Visibilities, but the calibration uncertainties are lower. Telescope/Bands L-band M-band N-band AT(with FT) 1.8/S0.6 8/S0.3 160/S0.7 UT(no FT) 0.6/S0.8 0.8/S0.4 9/S1.4 UT(with FT) 0.3/S0.8 0.5/S0.4 9/S0.7 Table 4: Differential Visibility uncertainties (%) in SiPhotmode . Closure Phase errors given in millirad Telescope/Bands L-band M-band N-band AT(with FT) 20/S20 66/S14 360/S14 UT(no FT) 7/S20 9/S14 30/S14 UT(with FT) 3.5/S20 5/S14 20/S14 Table 5: Closure Phase uncertainties. The BCD is used. One millirad is 0.057 degrees. MATISSE Science Analysis Report 5 Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 8 of 64 REQUIREMENTS DERIVED FROM SELECTED SCIENCE CASES Based on high-priority science cases selected from [RD1], requirements for the sensitivity and accuracy of the measurements with MATISSE are derived. In particular, following observational quantities are considered: visibilities, closure phases, differential phases, and differential visibilities. For each case we discuss the scientific background and the physical models used to simulate the observations. Then we present the observable measures that such models would produce and compare them with the MATISSE performance figures specified in the preceding section to see if MATISSE can indeed contribute to our understanding of these targets. We also discuss the number of targets available for observation under different assumptions such as UTs versus ATs, and with or without an external Fringe Tracker. 5.1 Primary Science Case: Star and Planet formation 5.1.1 NIR/MIR long-baseline interferometric observations of circumstellar disks Circumstellar disks around pre-main sequence stars play a key role in the formation of the stars themselves, as well as in the formation of planetary systems around the host star. Table 6: Number of papers published on YSOs sorted by instrument. There is a significant overlap between AMBER and MIDI, leading to a total number of YSOs observed with the VLTI of ~10–15 (source: olbin.jpl.nasa.gov). Note that the number of targets published is not the number of sources successfully observed. Astrophysical object (total number of publications interferometric observations) T Tauri stars Herbig stars Debris disks Massive YSOs (34) (50) (11) (8) Instrument AMBER 1 17 1 2 MIDI 6 10 1 6 Keck-I 15 6 0 0 The AMBER and MIDI instruments have started to observe the brightest protoplanetary disks in the infrared sky (Table 6). The current capabilities of other observatories are similar (see the comparison with the Keck-I). While the closure phases, delivered by AMBER, have allowed for first simple images of circumstellar disks (e.g. Kraus et al. 2010, Nature, 466, 339), the single-baseline MIDI observations concentrated on resolving MIR continuum size scales for the first time (e.g. Leinert et al. 2004, A&A, 423, 537; di Folco et al. 2009A&A, 500, 1065). The combination of data from both instruments helps to constrain the details of the dust distribution (e.g. Acke et al. 2008, A&A, 485, 209), but ambiguities remain due to the large gap between the currently available wavelengths and the poor uv-coverage. These shortcomings of existing interferometers are particular apparent, when studying more complex objects, like transitional YSO disks, which are in the process of dissolving and transformation. First interferometric observations have confirmed, that the characteristic Spectral Energy Distribution of transitional disks is due to dust depletion in the inner disk, probably opened up by a low-mass companion or planet (Pott et al. 2010, ApJ, 710, 265). In addition to such spatial complexity, the surroundings of young stellar optics, resolved by interferometers, also show temporal changes on monthly scale, thus high observing efficiency is required to monitor and understand changes in the disk structure. Such observing efficiency combined with calibration precision cannot be MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 9 of 64 provided by the current generation of MIR interferometers. The VLTI 1st instrument generation was also used to pioneer two further directions of disk and planet formation research. In our own solar system, a few asteroids have been observed by MIDI (e.g. Delbo et al. 2009, ApJ 694, 1228), demonstrating the feasibility to characterize solar system minor bodies with interferometry. In contrast, extrasolar planet detections and/or characterization with interferometry have so far not reached enough dynamic range to successfully observe any of them (see e.g. Matter et al. 2010, A&A 515, 69 or Millour et al. 2008, SPIE, 7013, 41 and Absil et al. 2010, A&A, 520, 2A). To learn more about planet and star formation by interferometric observations, MATISSE is designed to provide more baselines, new observing wavelength, spectroscopy and high-precision differential visibilities and phases, and closure phases, which were not provided by MIDI. At least four science cases in this context stand out which highlight particular observing capabilities unique to MATISSE: (1) Transitional disks Unique MATISSE capability: model-independent, sensitive 4T-imaging has particular strengths for morphologically non-trivial disks with asymmetries, clumps, gaps, etc. (2) Detection of faint companions Unique MATISSE capability: 4T- and combined L-N operation Parallel L-N band operation does help here since the number of source photons is increased, and part of the noise is correlated between simultaneous L and N observation (thinking of differential phase detection methods). Of course combined L-N operation will be interesting for variable sources, as well. (3) Physics of circumstellar disks Unique MATISSE capability: Adding LM to existing and near-future HK and N Such broad wavelength coverage will help to remove ambiguities from disk modelling, in particular at which radii which dust species are located. This will also improve our understanding of disk evolution processes. (4) Distribution of gas vs. dust Unique MATISSE capability: spectral resolution combined with 4T-imaging Wavelength-differential, spectro-interferometric imaging will reveal the location and kinematics of gas wrt. dust, exploiting the high precision of differential phase In the following sections we will focus our modelling efforts on the T Tauri and the Herbig sources. Furthermore, various aspects related to the dust and gas phase in this region and the feasibility to perform these observations with MATISSE are evaluated. In order to assess the MATISSE requirements, the following sections focus on: Definition of scenarios for different YSOs models, based on a Monte Carlo radiative transfer simulations, in order to assess what astrophysical issues can be studied with MATISSE and what requirements on the precision of the observables are needed, Estimation of the performance of different image reconstruction algorithms to evaluate the MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 10 of 64 feasibility of imaging and assess what typical image features can be reliably reconstructed. Two cases defining the input data accuracies are considered. Potential targets: Evaluation of the number of available YSOs as a function of the instrument sensitivity. 5.1.2 Feasibility studies (I): N band, Continuum 5.1.2.1 Goal Definition of the requirements in term of accuracy on the visibility and phase closure and evaluation of the proposed Image Reconstruction Algorithms 5.1.2.2 Definition of science cases In comparison to a reference model for a circumstellar disk around a Herbig star, the impact of various disk parameters on MATISSE observables (and required accuracy) is investigated in particular for the N band. The following disk parameters are considered: Inner disk radius Inclination angle Upper grain size Chemical composition of the dust and its dependence on the location in the disk 5.1.2.3 Model setup The central star is a Herbig star with an effective temperature of 10.000K and a radius of 2.27 Rsun. It is surrounded by a flared disk with parameters comparable to those derived from high-angular resolution imaging observations and subsequent modelling (see Equ. 1; see also [RD1]). ( r, z ) ~ r 1 z 2 exp , 2h with scale height h ~ r Eq. 1: Disk density distribution (=2.37, =1.29) The disk is assumed to be inclined by 45° from face-on, located in a distance of 280pc. The total disk mass is set to 10-4 Msun with a gas-to-dust mass ratio of 100:1. The inner disk radius of the reference model amounts to 3 AU. The outer disk radius is set to 100AU, its scale height at 100 AU is 15AU. The dust parameters are those derived for the interstellar medium (size distribution: 5nm-250nm, size distribution exponent: -3.5; composition: 62.5% astronomical silicate, 37.5% graphite). In order to generate the required SEDs and mid-infrared images, we simulated the radiative transfer with MC3D v.4 (see, e.g., Wolf, "MC3D - 3D Continuum Radiative Transfer, Version 2", 2003, Comp. Phys. Comm. 150, 99; S. Wolf, Th. Henning, B. Stecklum, "Multidimensional Self-Consistent Radiative Transfer based on the Monte Carlo Method", 1999, Astron. & Astroph. 349, 839; MC3D at www.astrophysik.uni-kiel.de/~star/). Based on the reference model, the following scenarios are discussed: Scenario 1 Figure 1 represents the simulated 10 micron image for scenario 1, which is the reference model. The MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 11 of 64 cut in this figure shows the contributions of the thermal emission from the dust and that of the scattering of the central source radiation by the dust particles. At this wavelength and for the dust grain size used, scattering is negligible as compared to the thermal emission of dust. Figure 1: Log of the 10 microns simulated image of scenario 1. The side length of the image is 0.214", its pixel scale 1.066 mas. b) Contributions of the dust thermal emission and of the dust particle scattering. Scenario 2 Inner rim radius changed from 3 AU to 4 AU The inner rim size is a relevant astrophysical parameter which has been measured for a large sample of sources. Several tens have been measured and are represented in Figure 7 of Absil & Mawet (2009). Important parameters that may determine the inner disk radius are the dust sublimation temperature, the presence of optically thick gas inside the inner rim, the decrease of accretion rate, and truncation by magnetic fields. The inner rims are hence important diagnostics of the disks. Scenario 3 Inclination angle of the disk changed to 35° The sensitivity of MATISSE to the inclination angle of the disks is of interest for comparing the inner parts of the protoplanetary disks to the external part which are studied by radio interferometry like IRAM at Plateau de Bure and soon by ALMA. This inclination angle parameter is of importance for testing the planarity of the different parts of the disks or detecting and understanding possible warps. Scenario 4 Maximum grain size three times bigger than in reference model The goal is to investigate whether MATISSE observations will allow one to confirm grain growth. Earlier studies have shown that the dust grains around young stars are generally significantly larger and more crystalline than in the interstellar medium (Absil and Mawett 2010 A&ARv 18, 317). Scenario 5 Dust grains containing 10%-40% of crystalline (olivine) material Definition of the requirements for MATISSE to perform a careful study of dust grain processing, motivated by the significant results achieved with MIDI (van Boekle et al. 2004). Here, the study of three HAeBe sources showed that the difference between the inner disk visibility shape and the outer disk visibility indicates a difference in dust mineralogy, with more crystalline grains in the inner parts. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 12 of 64 Scenario 6 Derived from Scenario 5: Crystalline material located only between 3 and 6 AU (modeling for scenario 6 failed). The scenarios 1, 2, 3 and 4 are simulated for two single wavelengths: 3.5 and 10.5 µm. Several wavelengths are simulated for the scenarios 5 and 6, as well as for scenario 1 in a second step: 3.20 µm, 3.35 µm, 3.50 µm and 3.75 µm for the L band, 7.50 µm, 8.00 µm, 8.50 µm, 9.00 µm, 9.50 µm, 10.00 µm, 10.50 µm, 11.00 µm, 11.50 µm, 12.00 µm, 12.50 µm, 13.0 µm for the N band. 5.1.2.4 Feasibility analysis: Required Visibility and Closure Phase We investigate the accuracy of the visibility and closure phase which is required to distinguish the various scenarios. For this purpose, we use the ASPRO software (http://www.jmmc.fr/aspro_page.htm) to simulate a realistic uv-coverage, and compute visibilities and closure phases corresponding to the different scenarios. We use a set of 3 configurations with 3 telescopes aiming at producing baseline variations in the range 20 meters – 150 meters with different orientations. A set of nine typical visibilities and 3 phase closures are produced in order to compare the model signatures. Most of the curves are shown in Figure 2 and Figure 3 for a first ensemble of simulated images corresponding to scenario 1, scenario 2, scenario 3 and scenario 4. For these 4 scenarios only one image was simulated, at 10.5 m, and the curves represented as a function of the wavelengths are extrapolated under the grey case assumption, which means that the variations with wavelength only reflect the changes in spatial frequency. The grey case does not justify chromatic plots of the visibilities versus wavelength and it is implemented here only for comparison with former, MIDI-like representations. In the second series of curves, scenarios 1, 1b (grey case of scenario 1, for comparison), 5 and 6 one can see the imperfections introduced by the grey case extrapolation, since this second series of simulations involves physical calculation of the images at the following wavelengths: 3.20 µm, 3.35 µm, 3.50 µm and 3.75 µm for the L band, 7.50 µm, 8.00 µm, 8.50 µm, 9.00 µm, 9.50 µm, 10.00 µm, 10.50 µm, 11.00 µm, 11.50 µm, 12.00 µm, 12.50 µm, 13.0 µm for the N band. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 13 of 64 Figure 2: A first ensemble of simulated visibilities corresponding to scenario 1, scenario 2, scenario 3 and scenario 4. These 4 scenarios differ from the change of the inner rim size, the change of the disk inclination and the change of the dust grain size. For these 4 scenarios only one image was simulated at 10.5 m and the curves are extrapolated under the grey case assumption. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 14 of 64 Figure 3: A first ensemble of simulated closure phases corresponding to scenario 1, scenario 2, scenario 3 and scenario 4. These 4 scenarios differ from the change of the inner rim size, the change of the disk inclination and the change of the dust grain size. For these 4 scenarios only one image was simulated at 10.5 m and the curves are extrapolated under the grey case assumption. Derived tolerances of the visibilities and phase closure errors The differences in the signatures induced by changes in inner rim radius, inclination and dust grain science are of order 1-10% in visibility and 0.05-1 radian in closure phase. These then directly represent the MATISSE required accuracies needed to discriminate these crucial astrophysical quantities. Please note that the variations assumed for the astrophysical quantities are relatively large. It is valuable to discriminate variations in these astrophysical parameters at a level of 10% of that assumed in the above simulations. As a goal we can try to achieve correspondingly finer tolerances in the measured quantities. From Tables 4 and 5 we read that the MATISSE N-band differential visibility and closure phase errors are about 1 % and 20 mrad for strong sources, which are adequate. However, the noise contributions for weaker sources are significant. To achieve 3% differential visibility errors, an N-band flux of 50 Jy (AT) or 3 (UT) is required. To achieve 100 mrad closure phase error, N-band fluxes of 3.6 Jy (AT) or 200 mJy (UT) are needed. We see that closure phases may be considerably more sensitive measures than visibilities. The curves below (Figure 4 and Figure 5) represent the visibilities and phase closures for scenario 1, 1b, 5 and 6. Scenario 1 is now simulated in the multi-chromatic case, one brightness map/image is simulated each 0.25 m of wavelength. The scenario 1b is a reminder of the former scenario 1 made in the grey case. The scenario 1 and also the scenarios 5, 6 are simulated in the multi-chromatic case. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 15 of 64 Figure 4: A second ensemble of simulated visibilities corresponding to scenario 1 (in multichromatic case now), scenario 1b (the former scenario 1 under the grey case assumption), scenario 5 and scenario 6. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 16 of 64 Figure 5: A second ensemble of simulated closure phases corresponding to scenario 1 (multichromatic case now), scenario 1b (the former scenario 1 under the grey case assumption), scenario 5 and scenario 6. There is a difference in the signature between scenario 1 and scenario 5. For the purpose of comparison, scenario 1b is here presented, illustrating the limitation of the grey case, strongly different from scenario 1 in multi-chromatic situation when we depart from the central wavelength of 10.5 m. The scenario 6 must be considered as failed since we had to cut imperfectly by software two different zones of the disk to simulate a radial variation of the degree of crystallinity in the disk. Hence our comparison will then be at this second stage limited to the scenario 1 and 5. These 2 scenarios show signature differences in the visibilities ranging from 1 to at most 5 percent. The differences in the phase closure are in the range 0.02-0.1 radian. These differences directly represent the accuracies required from MATISSE in order to be able to discriminate the fraction of crystalline material. Figure 6 below displays the differences in the spectra between scenario 1 and scenario 5 caused by different degrees of crystallinity: 10%, 20% and 40% (40% is the value used in the previous visibilities and closure phases representations). Crystallinity determination down to a 10% level is more exigent and would require, by scaling from the 40% case, a visibility accuracy of at worst a few percent of accuracy to distinguish between scenario 1 (amorphous dust) and scenario 5. The absolute visibility accuracy measurements are difficult to achieve in the N-band. Spectral signature of the crystalline material could be better evaluated in the differential visibilities. The closure phase requrements (say ~50 mrad) can be met for sources stronger than about 7 Jy (AT) or 0.6 Jy (UT). MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 17 of 64 Figure 6: Differences in the wavelength spectra between scenario 1 and scenario 5 with 10%, 20% and 40% of crystalline dust grains in the disk. The Figure 6, displayed with a spectral resolution of nearly 100, also illustrates the importance of a medium spectral resolution in N band in order to be sensitive to the sharpness of the expected features. We conclude that the signatures in the visibilities and closure phases, that can be used to distinguish between the different scenarios tested, require accuracies less than 5 percent in the visibility measurements, and of 0.1 radian in the closure phase measurements. 5.1.2.5 Simulated observations We now simulate the uv coverage using the ASPRO software, and then compute visibilities using the prototype of the Exposure Time Calculator of MATISSE [RD5] that produces errors on the measurements in accordance with the MATISSE Performance Analysis report. We simulate a set of different telescope configurations for a 4-telescope, 7 night observation. The stations used are the following: A1-B2-C1-D0 A0-G1-I1-K0 D0-H0-G1-I1 A0-B5-J6-M0 A0-B0-C1-D1 A0-G1-J2-J3 B5-E0-L0-G1 The three first configurations are those proposed by ESO currently and can be used for comparison with the 3 night simulated observations used during Phase A for reconstructing an image from scenario 1. From the 3 night / 3 configuration simulations [RD1, Phase A] we concluded that the sparse coverage of the uv plane was the strongest limitation on the image reconstruction process and that measurement errors as large as 10% did not further diminish the quality of the results. The present Science Analysis Report shows that satisfactory results can be expected indeed from an accuracy of 10 % on the visibility, however an accuracy of 2%-3% is highly desirable. Such a better accuracy a) is required to detect spectral signatures like the ones of the crystalline dust material, and b) would permit to improve the quality of image reconstruction assuming a good uv coverage is ensured. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 18 of 64 A better convergence of the image reconstruction, tested here through the use of different algorithms, is ensured when the accuracy on the visibility is improved (Figure 13 ). We now consider the impact on this conclusion by increasing the number of configurations to 7 with a correspondingly better uv coverage. Currently, four three-telescope reconfigurations, distributed over ~1 month, have been effectively done several times, and enable the VLTI to produce images of stellar surfaces and stellar environments. It does not appear unrealistic that 3 more reconfigurations could be done in the same amount of time (i.e., 7 nights of observations spread over ~1 month). We focus here on ATs observations. This enables us to simulate the 202m baseline to get the highest available angular resolution. The resulting uv coverage is shown Figure 7. Figure 7: UV coverage of our simulation. Left is for the three first nights and right is for the whole dataset (7 nights). Once the UV coverage is set, we use the scenario 1 images to simulate realistic observations using the prototype of the Exposure Time Calculator of MATISSE [RD5]. This step produces OI Fits datasets. This simulation is done under two assumptions: Case 1: Typical visibility error 10%, typical closure phase error 0.2 radians Case 2: Typical visibility error 2%, typical closure phase error 0.01 radians These 2 cases correspond to : Case 1: ◦ Integration time 900 seconds (15 mn), ◦ Chopping 0.5Hz, ◦ Closure phase systematic error set to 100 milli-radians (which is a pessimistic error, indeed from the AMBER Beam Commuting Device document – VLT-TRE-AMB-15830-7021, this systematic error is 23 mrd). Case 2: ◦ 1800 seconds of integration (30 mn), ◦ Chopping at 5 Hz ◦ No systematic error on the closure phase measurement, assuming BCD observations. Doc. Issue Date Page MATISSE Science Analysis Report VLT-TRE-MAT-15860-9008 1 01.03.2012 19 of 64 5.1.2.6 Data analysis: Image reconstruction In this section we present the different available imaging software for synthesising images from interferometric datasets. We recall here that, in principle, radio-interferometry software can be used to recover optical-interferometry images but that, due to practical reasons, specific softwares have been developed for this. We list in 6 the existing imaging software, both for optical interferometry and radio-interferometry. In this document, we focus on four software packages dedicated to optical/IR interferometry: BBM (developed in Bonn), BSMEM (developed at Cavendish University), MIRA (developed at the Lyon observatory) WISARD (developed by the JMMC) We compare their performance, ease of use, and results. Table 7: List of existing interferometric image reconstruction software. The four software tested here are presented first. Software BBM BSMEM MIRA WISARD AIPS Name stands for Building Block Method Bispectrum Maximum Entropy Multi-aperture Image Reconstruction Algorithm Weak-phase Interferometric Sample Alternating Reconstruction Device NRAO Astronomical Image Processing System Common Astronomy Software Applications CASA CITVLB DIFMAP MACIM Markov Chain Image reconstruction OYSTER RPR Recursive Phase Reconstruction VLBMEM VLB Maximum Entropy Method Algorithm BBM MEM Main access K-H Hofmann http://www.mrao.cam.ac.uk/research/OAS/bsmem.html Several http://www-obs.univ-lyon1.fr/labo/perso/eric.thiebaut/mira.html Several JMMC CLEAN http://www.aips.nrao.edu/ ESO : http://www.eso.org/sci/facilities/alma/observing/tools/dataCLEAN reduc.html MEM Caltech DIFMAP Caltech Markov Chain + MEM http://www.physics.usyd.edu.au/~mireland/MACIM/ CLEAN, DIFMAP C. Hummel / NPOI RPR ESO MEM http://www.astro.caltech.edu/~tjp/citvlb/vlbhelp/vlbmem.mem We first compare the interface of all software. Our comparison points are the following: Input files: only BBM uses ASCII files in a defined format, while the other software uses standard OI fits files. Input commands: all of the tested software are run via command-line (i.e. shell, yorick or IDL) functions, and their use can be scripted. Parameters used as input: all packages use pixel size, pixel number, regularization superparameter and prior as input. In addition, we tried (one has to keep in mind that such evaluation was made at the date of September 2010) to evaluate the runtime of one image reconstruction iteration. We define an iteration as “one run of the software with one set of parameters that gives as output an intermediate image”. Indeed, user interaction is needed at each iteration step until convergence of the software is reached (the convergence criterion itself being a subjective and user-dependent estimate of the image quality). We find that WISARD is one level below all other software, the computation time being the main limitation of the current use of this software. The BBM code could be optimized. BSMEM and MIRA are both very fast. Table 7 sums up this comparison. In terms of ease of use, BSMEM and MIRA clearly stands out as the more polished software, while BBM still has few aspects to improve (use of OI fits files, speed optimization) and WISARD stands MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 20 of 64 behind, the computing time being a main limitation. Table 8: The retained software for this study compared each other on “ease of use” criteria. Software Licence Who used it ? Code access Language Speed Input commands BBM K-H Hofmann K-H Hofmann Fortran ~5mn/iteration Cshell scripts BSMEM Case-by-case MEDC F. Millour F. Millour C++ <1mn/iteration shell scripts MIRA Gnu Public Licence (free) F. Millour Any Yorick + C <1mn/iteration yorick scripts WISARD JMMC M. Vannier M. Vannier IDL ~10h/iteration IDL scripts Regularization MEM MEM Several Several Input files ASCII files OI FITS OI FITS OI FITS We now compare the different software in terms of image reconstruction quality, in a similar approach as done at the interferometric “imaging beauty contests” in the frame of the biannual SPIE conferences. To perform this comparison, we use the simulated data from the previous part as input into the different packages. We then perform a visual comparison to a reference image made from the model convolved with a 130 m equivalent round aperture (Figure 8). Secondly, we compare cuts through the images in the axial and equatorial directions to verify the results of the visual inspection. Figure 8: The model used (left, linear scale) and the same convolved with a beam corresponding to a 200 m aperture telescope. The case 1 (standard errors) recovered images are shown in Figure 11. The visual inspection shows that all packages except WISARD yield reconstructions basically similar to the initial model. They all create artefacts which are different from package to package: BBM and MIRA produces “fluffy” images, whereas BSMEM gives two brighter “lobes” left and right of the annulus. Little or no faint extended structure is seen in the BSMEM image. Finally, WISARD gives qualitatively the right information (annulus with one side brighter than the other, extended flux), but the flux estimates are obviously far from the initial model. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 21 of 64 Figure 9: Image reconstruction in the case 1 (10% errors on visibilities) for the 4 software packages tested here. Qualitatively, all except WISARD can reproduce the features from the original object (annulus with one side brighter) MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 22 of 64 Figure 10 Case 2 (2% errors on visibilities) image reconstruction tests. Qualitatively, all packages give the same result. For case 2 (2% typical errors on visibilities), all packages give qualitatively similar results as shown in Fig. 12. The ring appears smoother in the case of BBM and MIRA, while WISARD and BSMEM produce unreal structures in it (“blobs” in several parts of the ring). To compare the results more quantitatively, we plot axial and equatorial cuts in the images and compare them with the original model image convolved with the 130 m aperture beam. The results are shown in Fig. 13. As found qualitatively before, WISARD provides the poorest match to the model. We also find that BSMEM, while being able to reconstruct the ring with proper flux ratios, is not able to match the faint extended structures in the disk. The last two software packages, BBM and MIRA, provide the best fidelity to the original model in both noisy and less noisy simulations. We find that the MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 23 of 64 noise level has an impact on the reconstruction of the faint structures of the image. These are of high importance in many aspects of the image analysis e.g. finding temperature gradient structures in the disk. For the 2% errors case, BBM is able to marginally recover flux from the central star, where all other packages fail to do so. Figure 11 Comparison of the image reconstruction results with cuts in the axial and equatorial directions. This gives a more quantitative estimate of the image reconstruction quality. Black line is the model convolved with the 130 m aperture beam, green line is the MIRA reconstruction, blue line is the BBM reconstruction, pink line is the BSMEM reconstruction, and red line is the WISARD reconstruction. Our conclusion from this comparison is that MIRA and BBM provide the best image fidelity, with a slight advantage for BBM. BSMEM provides less accurate results, although this may come from our more limited experience with this package. Finally, WISARD provides the poorest image fidelity, which may be linked to the very large computing times involved in its usage. These results are in line with the Beauty contests except for the BSMEM software. These differences should be investigated in the future, in particular, whether the fidelity can be increased by careful tuning of the parameters. In terms of use, MIRA and BSMEM are the most advanced software (use of OI fits, calculation speed). BBM is second with no interface with OI FITS, while WISARD is impaired by its very long computing times. As a general conclusion on the image reconstruction tests made here, it appears that, while all software are able to qualitatively reconstruct the structures of our model (i.e. asymmetric ring + extended flux) only BBM and MIRA are able to reconstruct faint structures with some fidelity in the images of disks. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 24 of 64 BBM is also able to recover partly the star flux in a case where the data errors are improved. A new development, specific to MATISSE, is undergoing by K.-H. Hofmann to greatly improve the quality and speed of the MATISSE image reconstruction software, formerly based on the Building Blocks algorithm. This new IRS (Image Reconstruction Software) uses a different algorithm (bispectrum match + ASA-CG descent algoritm), which was tested with success on existing interferometric datasets (beauty contest + AMBER observations). The reconstructed images with this IRS match better the data than BBM. We also note that while it may be perceived that the UV coverage is the main limitation in the image reconstruction process, in the case of many-configuration observations and in the example presented here for MATISSE the limiting factor for recovering images becomes the accuracy of the observable quantities which are the visibilities and phase closures. 5.1.3 Feasibility studies (II): L (M) and N bands, Continuum 5.1.3.1 Goal Definition of the requirements in term of accuracy on the visibility and phase closure. Evaluation of the scientific importance of continuum observations in L (M) band with MATISSE. 5.1.3.2 Definition of science cases We consider the following two science cases: Science Case 1: Detection of inner holes and/or gaps in the potential planet forming region of circumstellar disks Motivation: Inner holes and/or gaps are predicted signatures of disk evolution (disk dispersal), planet formation (grain growth with corresponding decrease of the disk opacity), and planet-disk interaction. Science Case 2: Detection of local brightness asymmetries in the potential planet forming region of circumstellar disks Motivation: Local brightness asymmetries are predicted signatures of disk evolution (e.g., locally enhanced scale height due to local over-densities), disk-planet interaction, and embedded companions For a more detailed scientific background of the outlined science cases, see [RD1]. As circumstellar disks are known around sources of different intrinsic brightness, both science cases were evaluated in the case of a disk around a Herbig star (Scenario 1) and a T Tauri star (Scenario 2). 5.1.3.3 Model setup The reference model for this study is similar to the one outlined in Sect. 5.1.3. For completeness, the entire model is outlined below. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 25 of 64 Disk and dust parameters A flared disk is used with parameters comparable to those derived from high-angular resolution imaging observations and subsequent modelling (see Equ. 1 - Sect. 5.1.3; see also [RD1]). The disk is assumed to be inclined by 30° from face-on, located in a distance of 140pc. The total disk mass is assumed to be 10-3 Msun with a gas-to-dust mass ratio of 100:1. The inner disk radius of the reference model amounts to 1.0AU in the case of the Herbig star, and 0.1 AU in the case of the T Tauri central star (and thus close to the sublimation radius). The outer disk radius is set to 100AU, its scale height at 100 AU amounts to 15AU. The dust parameters are those derived for the interstellar medium (size distribution: 5nm-250nm, size distribution exponent: -3.5; composition: 62.5% astronomical silicate, 37.5% graphite). Photospheric model Blackbody radiation: (Scenario 1) Herbig star: (Scenario 2) T Tauri star: 10.000K, 2.11 Rsun 4.000K, 2 Rsun Simulation of ideal images As thermal reemission is of importance in the L to N band wavelength range, the temperature structure is calculated self-consistently. Subsequently, wavelength-dependent images are calculated, taking both, thermal reemission radiation of the disk and scattered stellar light on the disk upper layers into account. The pixel scale of the images amounts to 0.714mas/Pixel which is about a factor of 4-5 smaller than the highest resolution MATISSE will achieve (L band, longest AT baselines). We simulated the radiative transfer with MC3D v.4 (see, e.g., Wolf, "MC3D - 3D Continuum Radiative Transfer, Version 2", 2003, Comp. Phys. Comm. 150, 99; S. Wolf, Th. Henning, B. Stecklum, "Multidimensional Self-Consistent Radiative Transfer based on the Monte Carlo Method", 1999, Astron. & Astroph. 349, 839; MC3D at www.astrophysik.uni-kiel.de/~star/). 5.1.3.4 Evaluation: General comment (1) As shown in Fig. 12, a major complication of continuum observations in L band – as compared to N band observations – is the significantly lower ratio of the disk-to-stellar flux. This is primarily due the fact that the disk brightness is mainly given by the scattered stellar light in L band, while in the N band the additional disk reemission becomes important. Figure 12 L and N band brightness distribution along the long major axis of the (inclined) reference disk in the case of a T Tauri central star. The overall flux in N band is higher than in the L band except for the central source (R= 0AU). MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 26 of 64 (2) Approach of this feasibility study: Comparison of simulated visibilities for the reference model outlined above and a modified disk model Due to the close proximity in wavelength of the L and M bands, only the results for the L band are presented here. For the selected science cases, the qualitative and quantitative conclusions for the M band are very similar to those for the L band. 5.1.3.5 Evaluation: Science case 1 (inner holes, gaps) Scenario 1 (disk around Herbig star) Configurations considered: a. Inner hole with radius 2 AU and 4 AU (reference disk: inner radius at 0.1 AU). These models are labelled in the plots below as 02 and 03 respectively. b. Gap between 2-3 AU and 4-5 AU (here, the increase of the local scale height at the outer gap boundary due to direct illumination by the central star has been taken into account. Furthermore, it has been further increased by a factor of ~2.5 to pronounce the effect). These models are labelled 21 and 31 respectively. Simulated fluxes and visibilities: In Figures 13-14 the resulting simulated fluxes and visibilities as a function of baseline are shown for the L and N band. The corresponding reference model is marked in black. The visibilities are low (max ~0.5 for all assumed models), allowing easy distinction between the science case model and the reference model, in both L and N band. For each model and band a range of baselines can be found where the difference in visibility is as large a factor of ~2-3 as compared to the values for the reference model (for example see Fig. 14 model 21 in the L band at a baseline ~ 90 m). In absolute numbers, the differences are in the range of V~0.2. Figure 13 Left:Simulated L-band correlated fluxes as a function of baseline [m] for Science Case 1 Scenario 1(HAe star) Right: Corresponding N band models. The different colors plots data for the different models described above. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 27 of 64 Figure 14 Same models as preceding figure but now plotting visibilities (normalized by photometric flux) Comparison to MATISSE specifications We discuss this “standard” science case in terms of both instrumental sensitivity, and the need for an external fringe tracker. We first discuss the relations between how the sources appear to MATISSE (K- and L-band) and how they appear to the fringe tracker (K-band and shorter wavelengths). Fringe Tracker considerations We have also modelled the sources discussed here in the K-band. From these experiments, we conclude that : The sources a K-band are usually very small, with visibilities ~1 In the L- and N-band models presented here, the visibilities are lower but if we are considering stars with weak apparent fluxes, these will be either farther away, or less luminous, than our models, and hence be smaller. For the calculations concerning the fringe tracker we can also assume that the visibilities of these stars at L- and K-band are near unity. At shorter baselines, the ratio of the K/L fluxes for the models presented is typically ~0.5. The ratio of K/N is typically ~0.06. Thus in converting the a given tracker sensitivity in Jansky to a minimum source flux in the scientific bands for use in the plots in Figures 23 and 24, we must divide by 0.06 and 0.5 respectively The sensitivity of Fringe Tracker designs is usually specified as a faintest correlated K-magnitude for reliable tracking. For proposed VLTI 2nd generation fringe trackers this limit is usually in the range K=8-12. For the primary science cases we have also modelled the coherent K-band flux from the simulated sources. For convenience we present a table of conversion from K-magnitude to K-band flux, assuming K=0 corresponds to 670 Jy. K=8->0.4 Jy K=9->0.17 Jy K=10->0.067 Jy K=11->0.027 Jy K=12->0.011 Jy Table 9 Conversion of K-magnitudes to fluxes. Observability of targets for Science Case 1 Scenario 1 (HAe stars) Comparison of the above figures to the values in Tables 1, 2, and 3 allows us to conclude: All models can be self-tracked with the UTs at both bands. Only the brightest models can be self-tracked with the ATs, so use of the ATs, with their more complete UV-coverage, will in MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 28 of 64 general require an external fringe tracker. The L-band fluxes are ~1 Jy so the K-band fluxes will be ~0.5 Jy. This corresponds to a tracker with K-band limit of magnitude ~8. The UTs without fringe tracker, and the ATs, with fringe tracker, will in general have sufficient sensitivity and accuracy to distinguish between the models in this scenario. Scenario 2 (disk around T Tauri star) The configurations considered are labelled in the colored plots below: a. Inner hole with radius 1 AU (model 01) b. Inner hole with radius 2 AU (model 02) c. Gap between 1-2AU (model 11) d. Gap between 2-3AU (model 21) e. Reference disk: inner radius at 0.1 AU Here, the situation is more complex. Because the exciting stars are less luminous, the warm dust zones emitting in the mid-infrared are less luminous and smaller. First, the detection of spatial structures in the N band is feasible. We confirm this result of the image reconstruction studies outlined in Sect. 5.1.3 and [RD1]. The simulated fluxes, visibilities and closure phases are shown in Figures 15, 16, and 17 (N band on the right hand side). Furthermore, in nearly all N band models we can distinguish between reference and science case model (differences are in the range V~0.2…0.5). Figure 15 Simulated fluxes from Science Case 1 Scenario 2. Left: L-band, Right N-band. Reference model is black. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 29 of 64 Figure 16 Visibilities for Science Case 1 Scenario 2 Figure 17 Closure Phases for Science Case 1 Scenario 2 In the L band (left hand side of Figure 16) the simulated visibilities for most baseline lengths amount to ~0.9-1.0. However, in the particular case of a gap between 1 and 2 AU (model 21), the visibility decreases down to ~0.85. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 30 of 64 To summarize, it would be possible only to distinguish between selected disk configurations through L band observations. The main reasons are a) the larger error due to the significantly lower luminosity of the central sources (as compared to the case of Herbig stars) and b) the general higher visibilities (see Fig. 18 showing the compact brightness profile of the disk around the T Tauri vs. the Herbig Ae star). Figure 18 Radial L and N band brightness profiles of the HAe vs. TTauri disk (along the long major axis of the disk). Observability of Case 1 Scenario 2 (TTauri stars): With luck, the strongest targets can be self-tracked with the UTs. Generally most source models would require a fringe tracker even on the UTs. The L-band fluxes are ~0.2 Jy corresponding to K-band ~0.1 Jy. From Table 9 the fringe tracker sensitivity must exceed K=10. Distinguishing between models will require a sensitivity of better than 10 mJy at L-band and 100 mJy at N-band. In the more fortunate cases observations with the ATs are possible in Lband, but not in N-band. With the UTs the sensitivity is adequate in both bands. 5.1.3.6 Evaluation: Science case 2 (brightness asymmetry, T Tauri) Configurations considered: Reference model with an added point source at various radial distances from the center (0.5 AU, 1 AU, 2 AU, 5 AU, 10 AU). Brightness of the additional point source: 10% and 1% of that of the central star. The models with the 10% point source are labelled in the plots below as (A00, A01, A02, A03, and A04). along with the Reference. For the 1% point source we only display the 10 AU model as B04. Central star: T Tauri star Brightness of the additional source: 10% of the brightness of the central source The correlated fluxes, visibilities, and closure phases are shown in Figures 19, 20, and 21. In analogy to Science Case 1 Scenario 2, the visibilities are close to 1.0. However, in each considered case it is possible to distinguish between the modified disk (i.e., the disk with the secondary source) and the reference model. Even more, all models can be distinguished from each other. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 31 of 64 Figure 19 Science Case 2 (TTauri star, additional point source), Correlated Fluxes of the disk plus added point source: 10% of the brightness of the central source. Location of the secondary source: A00: 0.5 AU, A01: 1 AU, A02: 2AU, A03: 5AU, A04: 10AU. Left: L-Band, Right: N-Band Figure 20 Science Case 2, Visibilities MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 32 of 64 Figure 21 Science Case 2 Closure Phases Figure 22 Science Case 2 B04 point source added at 1% of flux of central source at 10 AU, L-band Visibilities and Closure Phases. Brightness of the additional source: 1% of the brightness of the central source L-band: In this case, the resulting L band visibilities of the disk with and without the secondary source are very high and can hardly be distinguished with the expected accuracy of ~2% (see Figure 22 for illustration). The closure phase differences are of order 2 degrees or 30 mrad, and the differences between the reference model and model B04 are much less, so in this measure the models are not distinguishable. N band: Similar calculations in N-band show that the visibilities and closure phases of model B04 and the reference model cannot be distinguished for the weak T Tauri stars (~300 mJy). MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 33 of 64 5.1.3.7 Summary Requirements on the visibility: summary Table 10 Note: The derived requirements for ΔV/V are valid for selected baseline ranges Science case Band Required ΔV/V A. Herbig stars: L N ~ 0.50 ~ 0.70 A. T Tauri stars L N ~ 0.10 ~ 0.70 B. Asymmetries L N ~ 0.17 down to 0.02 ~ 0.02 Remarks: (1) The evaluation (feasible/not feasible) is to be seen in the context of the considered model. (2) For the interpretation of the results for the Science case 2 it is important to consider that the brightness of the secondary source was relative to that of the central star. Thus, L band observations are particularly useful for the detection of illuminated structures in the disk or L band-bright (i.e., hot) self-radiating secondary sources. N band observations of local brightness asymmetries are also possible, but for N band-bright sources (see, e.g., [RD1] for an example of an embedded accreting proto-planet). However, the reference brightness relevant for the evaluation of the feasibility of these observations would be that of the hot inner rim of the dust disk, not of the N band-weak T Tauri or Herbig star. 5.1.3.8 Potential targets We evaluate the number of available YSOs as a function of the instrument sensitivity by taking our sample of sources containing protoplanetary and debris disks detections and parameters from the website www.circumstellardisks.org. The catalogue provides a library-like data base of the best known and observed sources, not the entire number of circumstellar disks observed. We limit our study to source declinations < 30° in order to get only sources observable from the VLTI. We collected the received fluxes from these sources from existing catalogues and from the literature. Based on the above catalogue, the total number of objects with a declination between 30° and -80° is 126. Among these sources, our search of available photometric data reduces the sample to 73 targets in N band (58% of the initial source sample) and to 66 sources in L band (representing 52% of the initial sample). This translates into the following histograms for N band (Figures 23) that represent sources for all declinations and those with declinations between only 10° and -50° (Figure 23, left and right histograms respectively). MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 34 of 64 Figure 23: N band flux histogram of observed YSOs from our sample. The sample seems to be incomplete below 0.5 Jy. We note that the number of sources steadily increases from ~100 Jy to ~0.5 Jy, with almost no data below the 0.5 Jy level. This is probably due the limitation of the considered catalogue and/or the incompleteness of photometric surveys in the southern hemisphere. In addition, while the number of T Tauri stars increases with decreasing flux, the number of Herbig stars does not. This may be related to the way Herbig stars are detected (spectroscopically) compared to T Tauri stars (JHK photometry). While the catalogue used and recognized by the community for the study of circumstellar YSO disks is probably incomplete, it is still useful to assess the MATISSE requirements in term of sensitivity. In Figure 24 we present the same histogram for the L band. Figure 24: L band flux histogram of observed YSOs from our sample. We note that the sample seems to be incomplete below 0.5 Jy. The requirement for MATISSE is to access to a significant enough number of sources. Having a the source sample accessible with MATISSE larger than a few tens for the YSO category (30-40 sources) will allow to have good understanding and statistics on the astrophysical parameters. Remark : Recent progress on the data reduction side in the context of the MIDI AGN large program pushed the MIDI stand-alone sensitivity limit to about 0.2Jy. Down to this level, fringes can be reliably recorded and calibrated (Kishimoto et al. 2011; Burtscher et al. 2011, PhD thesis). This level can be pushed even further by another factor 4..5 with external fringe tracking, as demonstrated with the PRIMA fringe tracker (Müller, A. et al. 2010). The new MIDI faint source limits are significantly Doc. Issue Date Page MATISSE Science Analysis Report VLT-TRE-MAT-15860-9008 1 01.03.2012 35 of 64 increasing the number of available source for AT-observations. This is particularly important in the context of the imaging capabilities of Matisse, since the AT array offers a wider range of baselines, and thus higher dynamic resolution of the resulting images, than the UT array. We now use the MATISSE sensitivity estimates from Section 4, and the N(S) estimates in Figures 25 amd 26 to estimate the number of accessible targets. Without fringe tracker we take the limiting MATISSE fluxes to be L-band=1.9 Jy (AT) and 0.18 Jy (UT); in N-band 11.6 Jy (AT) and 0.7 Jy (UT). The numbers of observable sources brightest are then: N band: L band: ATs: ~ 5, ATs: ~ 12, UTs: ~ 35 UTs: ~ 30 The sources listed in the two bands are, of course, often the same sources. These numbers are consistent with those provided in Table 6 giving the number of papers published on YSOs sorted by instrument. These numbers are consistent also with the current evaluated numbers of studied young stellar objects by optical interferometry (approximately 30-40 sources; review article of Absil & Mawett, 2010). The number of potential UT targets is reasonably large, but those accessible to the ATs, which provide the UV-coverage necessary for good imaging, is rather small. We now consider the impact of an external fringe tracker on the AT numbers. For a given tracker sensitivity (Table 9) we divide the K-band flux by the above specified conversion factors to L- and N-bands (0.5 and 0.06 respectively), and use the plots to determine the number of sufficiently bright targets. With some conservative extrapolation of the plots to lower fluxes we find: K(tracker)= L-band N-band 8 20 7 9 25 8 10 30 12 11 35 18 12 >40 24 Table 11 Available YSO targets with ATs for given Fringe Tracker sensitivity 5.1.4 Feasibility studies (III): L and M band, Lines 5.1.4.1 Goal As it is specified in the Technical Specifications [AD1], MATISSE, in the L&M spectral band, has a maximal resolution of 950 in the L band only a maximal resolution of the order of 650 in M band (medium resolution in L&M). The present section evaluates the interest of a higher spectral resolution with an example which is the study of the CO lines at about 4.7 microns in the M band. Other very important emission lines are the Hydrogen lines, in particular the Br line at about 4.05 microns in L band. 5.1.4.2 Definition of science cases The medium and high spectral resolution modes of MATISSE provide access to high-angular resolution imaging of the inner regions of protoplanetary disks in gas emission lines. The brightest emission lines in the M-band include the fundamental rovibrational lines of CO near 4.67 micron, and several atomic hydrogen lines in the L band, such as Br Pf and Pf. The CO rovibrational emission traces gas within the inner few AU of the disk. The hydrogen lines, likely trace the disk wind region MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 36 of 64 (e.g., Weigelt et al. 2011, A&A 527, A103). Long-slit spectroscopy with instruments like NIRSPEC, CRIRES, and Phoenix resolve the individual rotational lines inside the rovibrational ladder up to Jlevels as high as 40, with line widths up to 50-100 km/s (e.g., Brittain et al. 2003; Blake & Boogert 2004; Rettig et al. 2004; Salyk et al. 2007). These observations do not spatially resolve the emission, but gas in Keplerian rotation is inferred from the velocity-resolved line profiles. In several cases (e.g., TW Hya and GM Aur; Salyk et al. 2007) gas is seen inside the innermost disk regions that have been cleared-out of dust. The amount of gas, however, is insufficient to maintain the observed stellar accretion rates, therefore indicating ongoing replenishment from the surrounding gas+dust disk. MATISSE will be able to spatially resolve the gas and dust emission (although not spectrally resolve the individual lines) and directly address the question of how the gas fills the inner disk regions. At a spectral resolution of ~1300, MATISSE can separate the individual lines within the rovibrational ladder of CO, and image the line and continuum emission separately. In the analysis below, we will focus on predictions for the fundamental rovibrational ladder of CO for a few disk geometries. Science case: Detection of differences in the spatial distribution of dust and gas in the potentially planet-forming regions of a circumstellar disk. Motivation: Spatially unresolved spectra suggest that inside the gaps and holes observed in protoplanetary disks in the continuum, appreciable amounts of gas are still present. Theoretical studies of planet-disk interactions suggest that, although planets can reduce the density in the gap/hole, the gas is not completely removed from this region. 5.1.4.3 Model setup We base the line models on the same disk structures as investigated in the preceding sections for the continuum emission (Sect. 5.1.4). For the dust density and temperature distribution as well as the stellar photospheric emission we used some of the same parameters used to simulate the continuum emission. The gas was assumed to be in Keplerian rotation around the central star with masses, of 1.0 Msun and 2.5 Msun for the T Tauri and the Herbig Ae star case, respectively. Outside of the perturbed region (hole/gap) we assumed that the spatial distribution of gas follows that of the dust with a fixed, uniform gas-to-dust mass ratio of 100 and a CO/H2 abundance of 110-4. Regarding the distribution of gas in the holes/gaps, seen in the dust distribution, we investigated three scenarios: Scenario 1: Scenario 2: Scenario 3: The gap/hole does not contain any gas, i.e., it is both dust- and gas-free. The gap/hole exists only in the distribution of dust, while the spatial distribution of gas is unperturbed. The gas is removed from the gap/hole except for a narrow spiral stream. This model represents a case where instabilities at the gap/hole edge cause some continued gas accretion. We describe the density distribution in the gap by (r rc ( )) 2 , (r , ) 0 exp 2 where 0 is the gas density in the unperturbed, reference model while is the standard deviation of the Gaussian that describes the radial width of the stream. The quantity rc() is given by MATISSE Science Analysis Report rc ( ) Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 37 of 64 (rgap,out rgap,in ) 0.7 rgap,in . Here is the azimuthal coordinate while rgap,in and rgap,out are the inner and outer radius of the gap/hole, respectively. For the gas kinetic temperature we assumed a value which is 1.3 times larger than the dust temperature at any location in the unperturbed reference model. The increased gas temperature matches the line luminosities observed in spatially unresolved long-slit spectra of young stars. The temperature of the gas is indeed likely larger than the dust temperature in the upper layers of protoplanetary disks due to UV/X-ray photons. We used the 3D radiative transfer code RADMC3D (Dullemond et al. in prep., www.ita.uniheidelberg.de/~dullemond/software/radmc-3d/) to calculate channel maps for five lines in the fundamental band of CO (v=1-0 P8-P12). The energy levels of CO are assumed to be populated according to local thermodynamical equilibrium (LTE). Einstein A coefficients, statistical weights and level energies for each transition were taken from Goorvitch 1994. After the level populations were obtained, channel maps were calculated with raytracing, placing the object at an orientation of 0 (face on) and 45. Channel maps were calculated at a high enough spectral resolution (R=31051.5106) to resolve the lines, which is necessary to calculate the line luminosity correctly. Raytracing was done only around the vicinity of the lines, +-8km/s in face on models and +-100 km/s for 45° inclination and the continuum images for the wavelengths in-between were calculated using linear interpolation. The high resolution channel maps were finally re-binned to the spectral resolution of R=3000. 5.1.4.4 Evaluation (1) Spectral resolution We calculated the spatially integrated photometric flux at each wavelength at different spectral resolutions (see Fig. 30). At a spectral resolution of several hundreds the line and continuum emission cannot be separated as each channel will contain both line and continuum emission, i.e., no clear continuum channel will exist. A resolution of at least R=1300 is required to separate the CO line and continuum emission, with pure line-free continuum separating the lines. Higher spectral resolution up to 3000-6000 will increase the line-to-continuum ratio, and therefore the signal-to-noise in the line emission, as the square-root of the spectral resolution as long as the individual lines are not spectrally resolved. Any higher resolution will spread the line flux over a larger number of channels, thus decreasing again the S/N. MATISSE cannot resolve the line kinematics, which are of the order of tens of km/s or resolving power of 10,000 or more. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 38 of 64 Figure 27. Spatially integrated spectrum of a model disk around a Herbig Ae star seen at 45° inclination angle. Five lines of the fundamental band of CO are shown at three different spectral resolutions. It is clearly seen that a spectral resolution of at least R=1300 is required to separate the line and continuum emission. (2) Sensitivity and ability to distinguish between different models We simulated observations with MATISSE using the ATs for a 15 min of integration time. The model source was placed at a declination of -40. The spectra were rebinned to a resolution of 1300. To evaluate how well MATISSE can distinguish between the three models with different gas distribution we compared the correlated (continuum-subtracted) line fluxes as a function of baseline. A) Herbig Ae stars Figure 28 shows the correlated line flux as a function of baseline for all three considered scenarios for a model with a 2 AU inner hole and a face-on (0) orientation. The source is well resolved in all three cases and the structural differences are visible in the curves. Scenarios 1 and 2 have symmetric source models, resulting in smooth visibility curves. The spiral arm pattern of Scenario 3 is not symmetric, resulting in a scatter of the points at similar projected baselines, depending on position angle. The average flux level in the correlated line flux is about 100-200 mJy at baselines longer than ~40 m, which is about the same as the average difference between the different models. Taking a flux uncertainty of 100 mJy for 15 min integration time on the ATs translates to a signal-to-noise ratio in the correlated line flux of 1-2 at baselines longer than ~40 m and 2-8 for baselines shorter than ~40 m. This is marginally sufficient to disentangle between the different scenarios. Therefore, only the brightest and closest Herbig Ae stars can be observed using only the ATs. However, we can gain a factor of at least 20 in signal-to-noise by using the UTs instead of the ATs, which makes the observations of most of the known Herbig Ae stars feasible with MATISSE. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 39 of 64 Figure 28 Disk around a Herbig Ae star: Correlated flux in the line centers as a function of baseline for all three simulated scenarios for the gas distribution with a 2 AU inner hole in the dust distribution, seen under a face-on orientation. B) T Tauri stars In Figure 29 we show the correlated line flux as a function of baseline for all three considered scenarios for a model of a T Tauri star and a surrounding disk with a 2 AU inner hole. There are two important differences between the Herbig Ae stars and the T Tauri stars that are strongly reflected in these curves. (1) The absolute brightness of T Tauri systems is lower than that of Herbig Ae stars by a factor of several tens, which decreases both the correlated and the total flux. (2) Due to the lower stellar luminosity the spatial extent of the emitting region is also smaller in T Tauri stars compared to Herbig Ae systems if they are seen at the same distance. This changes the visibility amplitude, decreasing the correlated and increasing the correlated flux. By comparing Figure 28 with Figure 29 it is clearly seen that the correlated flux of the T Tauri models is about a factor of hundred lower than the Herbig Ae stars. This means that even with the UTs the correlated flux can only be measured at the shortest baselines. This still allows us to distinguish between disks without a gap in the gas distribution, and models with a gap that is partially or fully evacuated in gas as well. However, to distinguish whether the gap is entirely empty of gas, or if a spiral-like gas streamer is present, is probably beyond the capability of MATISSE even using the UTs. Complementary long-slit spectroscopy, on the other hand, tells us whether gas is present at all inside the gap (via line width information), irrespective of the extent to which the gap is filled. Together, a more-or-less complete picture can be constructed. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 40 of 64 Figure 29 Same as for Fig.28, but here for a disk around a T Tauri star. Although the three different scenarios provide clearly different signatures in the correlated line fluxes, note the difference in the flux levels between the Herbig Ae (Fig 31) and the T Tauri cases. Fig. 30. Same as Figs. 28 and 29, but now for viewing angles of 45. The upper panel shows the case for a Herbig Ae disk, the lower panel for a T Tauri star. The histrograms show binned values for a bin width of 20 m. Figure 30 shows the corresponding simulation for a Herbig Ae disk and a T Tauri disk for a viewing angle of 45. Qualitatively, the strength of the signal remains the same. The largest difference with the MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 41 of 64 case of a face-on orientation is that the more oblique viewing angle introduces a spread of correlated fluxes for a given projected baseline, corresponding to the different position angles involved. Binning the fluxes, the simulated data still differentiate between the case where gas fills the gap, vs cases where the gap is empty of gas or only partially filled. When position-angle information is used (not shown), stronger constraints on the gas distribution inside the gap can be deduced, but never as clear as in the face-on case. 5.1.4.5 Summary The detection of differences in the spatial distribution of dust and CO line gas in the potentially planetforming regions of a circumstellar disk might become feasible for Herbig stars and appears difficult for the weak T Tauri sources. At resolution of R=1300 in M band would be required to separate the CO lines from the continuum R = 650 is the maximal resolution reached with MATISSE, with the medium L&M resolution, for the M band. The maximal resolution of MATISSE is 950 for the L band. It would allow to study the hoter gas counterpart of the disks. Hydrogen lines allow us to study the hot gas in the inner parts of the disks and the disk wind, as demonstrated by Brγ AMBER observations with R = 1500 and 12000 (e.g., Kraus et al. 2008, A&A 489, 1157; Weigelt et al. 2011, A&A 527, A103). The typical line widths of Hydrogen lines are in the range of 50 to 100 km/s. The Brα line in the L band has the advantage that it is brighter than the Brγ line in the K band. The maximal resolution of MATISSE in the L band is R = 950. At least R = 600 is required to image YSOs in Hydrogen lines (e.g., Brα line) with good SNR (e.g., Geers et al. 2007, A&A 476, 279). The Br line is at about 4.05 microns in L band. The spectral coverage allowed for the L&M band ranges between 2.8 and 5 microns of wavelengths (see the ‘Instruments Specifications’ document : RD6). The wavelength coverage for the L band high resolution ranges from 2.8 to 4.2 microns, covering the detector size. This coverage includes the Br line. MATISSE Science Analysis Report 5.2 Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 42 of 64 Primary Science Case: Active Galactic Nuclei 5.2.1 Introduction This section on AGNs will verify whether MATISSE as specified can add to our understanding the nature of AGNs, particularly our understanding of the dust structures, known historically as the “obscuring torus”, at parsec scales. Our methodology, similar to that used for the protoplanetary disks, is to consider a number of theoretical models of the dust with different characteristics, and investigate whether MATISSE can distinguish these models. We use as a basis the models published by Schartmann et al. 2008 (A&A 482, 67) where the dust disk is simulated as a set of optically thick clouds in a rotating flattened structure about the hot AGN core. The clouds absorb UV radiation from the core and reradiate it at infrared wavelengths. The clumpy structure of the disk has been indicated by both theoretical studies and MIDI observations. The models studied by Schartmann vary in the total dust mass, its radial distribution, its meridional distribution, and the degree of clumpyness. Additional we consider the effects of viewing angle with respect to the disk spin axis, since differences in the viewing angle are usually considered to be the origin of the Seyfert 1/Seyfert 2 dichotomy. We do not discuss the details of the models here, but in the figures below we designate them according to the figure numbers used in Schartmann 2008, and the inclination angles. In other words, the plots labelled f12a_10 or f12_70 refer to the models shown in Fig. 12a in Schartmann, viewed at angles of 10 degrees and 70 degrees from the spin axis, respectively. The 10 degree models may be taken to represent Sy 1 galaxies, and the 70 degree models Sy 2 galaxies. 5.2.2 Simulation results In the figures immediately below, we show the simulated correlated fluxes and visibilities measured by MATISSE in the 4-telescope UT configuration for an AGN at a declination of -40 degrees, and a distance of 40 Mpc. For reference the nearest few AGNs, besides our own Galaxy, are at distances of 4-15 Mpc. AGNs vary in total luminosity by many orders of magnitude. From physical scaling laws, a powerful AGN at a large distance appears similar to a weaker nearby AGN. The farthest Seyfert galaxies likely to be accessible to MATISSE are at distances up to 100 Mpc. The more powerful quasars, like 3C273, are observable to ~500 Mpc. Obvious scaling relations also exist when viewing AGNs of a given luminosity at different distances. If the distance doubles the visibilities will match at twice the projected baseline, but the correlated flux at this point will drop by a factor of four. For brevity we do not show every model considered, but only cases that illustrate typical values and the range of variation. Each plot shows the correlated flux or visibility of one model as a function of projected baseline, for five color-coded wavelengths: 3.5 (L-band), 4.6(M-band), 8.5, 10.1 and 12.0 (all N-band; to illustrate the changes across this wide band). MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 43 of 64 Figure 31 AGN correlated fluxes for model f6 at various wavelengths and at two inclinations Figure 32 AGN visibilities for model f6 MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 44 of 64 Figure 33 AGN correlated fluxes for model f12 Figure 34 AGN visibilities for model f 12 Summary of Simulations From the plots, and including information from the models not plotted: The AGN spectra are red: they are stronger at longer wavelengths in contrast to stars. This is because the emitting dust is relatively cool. N-band characteristics: most models well resolved, typical fluxes 200 mJy-500 mJy, typical visibilities 0.2-0.8 with model-model variations in the same ranges. M-band: also well resolved, fluxes 100-300 mJy, visibilities 0.2-1. L-band: some models partly resolved, others essentially unresolved, fluxes 0-250 mJy, visibilities 0.7-1.0 Considering the models more physically we see that the near face-on, 10 degree inclination, Sy 1, models show high visibilities and moderately red spectra; the edge=on, 70 degree Sy 2 models have lower visibilities and very red spectra: the L-band fluxes are extremely low. Both these phenomena arise because in the face-on models, the hot central core dominates the shorter wavelengths, while in the edge-on models, the emission from the core is extinguished by the intervening dust, and re-emitted at longer wavelengths and larger radii. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 45 of 64 The edge-on models show a larger scatter of visibilities at a given baselines; this is because these plots do not distinguish measurements at different position angles, so the major/minor axis projection effects at high inclination appear as scatter. At fixed inclination angle the scatter increases in models with fewer clumps, as the random variation in the positions of the clumps has then a larger effect. 5.2.3 Observability of AGNs with MATISSE Comparison of Figures 31 to 34 3434 to the performance values in Tables 1 to 3 allows us to conclude: For the reference model at 40 Mpc AT measurements without a fringe tracker are useless. In fact there are a very small number (~2) of nearer targets (c.f. MIDI publications) accessible to the ATs without fringe tracker. From the signal/noise point of view Seyfert 1 galaxies (low inclination, hot inner source) are observable at L- and M-bands with fringe tracked ATs or UTs. Even with the UTs, the fluxes are lower than the self-tracking limits (Table 1) so a fringe tracker will be necessary. At Nband they are marginally observable with fringe tracked ATs, and easily observeable with (fringe tracked) UTs. From the signal/noise values Seyfert 2 galaxies (edge-on, inner regions obscured) are marginally observable at L- and M-bands with tracked ATs and with UTs. In N-band they unobservable with ATs. They are too faint to self-fringe track at all wavelengths. Realistically this means that the nearest or most luminous sources can be observed without a fringe tracker. With an external fringe tracker the ATs are scientifically useful in the L- and M-bands, but only marginally so in the N-band 5.2.4 Fringe Tracker Requirements While producing the models just used, K-band correlated fluxes were also calculated in order to judge the possibilities of fringe tracking on the AGN nuclei. These varied in the same general fashion as the L-band fluxes, but more extremely. For the face-on models the typical K-band correlated fluxes were ~180-200 mJy (K~9.0). Edge-on models varied from 1-50 mJy (K=10.3-14). Thus to observe Sy 1 galaxies with one-beam, on-source, tracking requires a tracker with limiting K>9.0. Observing Sy2 systems requires K~11. Also a number of the more distant targets will be sufficiently near to a trackable foreground reference star. Estimates of the number of such targets are given below and range from ~3 at K(FT)=7 to ~40 at K(FT)=10. We conclude that the 2nd generation fringe tracker must be able to track stars with K-band magnitudes in the 10-11 range. 5.2.5 Number of targets versus sensitivity The nominal MATISSE sensitivity in blind mode at N-band is .6 Jy in 4-telescope mode, similar to the nominal MIDI sensitivity, although to date MIDI has been used to obtain correlated fluxes of AGNs down to 0.17 Jy. The nominal L-band sensitivity from the Performance Analysis is 0.1 Jy. For MIDI observations various lists of AGNs have been assembled, often based on the (inhomogeneous) list of Veron-City and Veron 2006 (A&A 455, 773) Limited baseline MIDI observations of these source yield the following estimates of the number of sources visible from Doc. Issue Date Page MATISSE Science Analysis Report VLT-TRE-MAT-15860-9008 1 01.03.2012 46 of 64 Paranal for specified N-band correlated fluxes: 3 targets> 1 Jy 8 targets >0.5 Jy (including the above 3) 15 targets>0.2Jy (including above) More complete lists of AGNs, derived from the Sloan Survey and equivalent VISTA surveys, will probably increase the number of southern AGNs in the weaker flux intervals by a factor of 2-3. The number > 1Jy will probably not increase, these are all very well-known sources. The expected correlated fluxes at L- and M- bands are not well known. Only a few sources have been observed interverometrically in the near- and mid-IR. NGC 4151, for example drops a factor of 3 in correlated flux between 10 microns and 2 microns. The sources in the MIDI AGN snapshot survey (Tristram et al., 2009, A&A 502,67) typically show drop in correlated flux for factors of 1.5-2 between 13m and 8m. With these spectral slopes, the L-band fluxes should be factors of 2-4 below the Nband (10 m) fluxes, consistent with the value for NGC 4151. These values are consistent with those found from the modelling procedures, with larger ratios being found for edge-on systems where the Lband flux is reduced by absorption. With these scaling factors the number of sources detectable in blind mode at L-band will be approximately: 3 targets > 0.2 Jy 15 targets > 0.1 Jy Thus in UT self-tracking mode, including the expectation of an expanded target list, we expect to be able to map 10-20 targets in N-band, 4-T mode, and ~5 targets in L-band 4-T mode. 5.2.5.1 AGN targets with an external fringe tracker We have also examined the number of targets with bright cores at K-band, or near (<30 arcsec) relatively bright reference K-band stars. The number is of course a strong function of the limiting magnitude of the fringe tracker. The tables below give approximate numbers of southern targets for different K-band limiting magnitudes (derived from the Veron-Cetty, Veron list) and can perhaps be multiplied by 2 for a more complete AGN list. K(tracker)= N(AGN core) N(ref star) 8 1 (NGC 1068) 5 9 1 21 10 9 40 11 30 >40 12 >40 >40 These numbers should be ~4 times larger if reference stars within 60” are included, but this has not been verified, nor whether MATISSE will produce useful images at this separation. This is particularly doubtful at L-band. The single-beam versus dual-beam AGN target lists are (mostly) nonintersecting sets. Approximately 10 AGN targets are available at the nominal MATISSE performance limits in blind mode or internal tracking mode. To significantly increase this number, an external tracker with K_lim >~ 10 is necessary. MATISSE Science Analysis Report 5.3 Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 47 of 64 Secondary Science Case: Evolved Stars Compared to the N band first explored by MIDI, the L band remains a relatively unexplored region and a few studies can be reported in the field of evolved stars. In this section, the focus will be particularly on the L and M bands, and the study of evolved, very bright sources at the highest spectral resolution. Arguments will be provided to have the highest possible spectra resolution in the L and the M bands, based on the MATISSE performances described in Sect.4. 5.3.1 Hot stars surrounded by disks Many disks are encountered around evolved stars that were studied with the first generation VLTI instruments AMBER and MIDI. These studies suffer from the lack of homogeneity between the AMBER dataset and the MIDI one. Generally, due to the 3T recombination of AMBER, the amount of data presented is much larger than for MIDI, including observable such as the closure phase. The characteristics of these disks are very close to those of some passive disks found around the hottest YSOs, namely the Herbig Ae and Be stars, and many conclusions reached in Sect. 5.1. can be applied for these sources. There is, however, a critical intrinsic difference between YSOs disks and disks found around evolved sources. Disks observed around YSOs are accretion disks surrounding a single or multiple stellar sources. By contrast, the disks observed around evolved stars are formed by mass-loss, and in most cases by mass-exchange within a binary system. B[e] stars are hot objects (O, B type) that surprisingly exhibit strong IR excess related to a compact dusty environment. This spectral type is not related to a determined evolutionary state but cover a vast variety of stars that interact in binary systems (including some early-type YSOs in multiple systems). The only exception to this trend is the disks encountered around the fast rotating Be stars that are probably formed independently from the fact that the star is single or multiple. At low spectral low resolution, and using the imaging capabilities of MATISSE, the systematically redundant LM/N bands of the MATISSE observations will allow one to tightly constrain the radial dependency of the temperature gradient in disks, providing invaluable constraints on their density and temperature structure. There is a particular interest of detecting any direct or indirect signature of binarity. Directly by detecting point sources in the vicinity of the source, and indirectly by detecting spiral arms or rotating inhomogeneities in the disk. The medium spectral resolution is much appropriate to study the dusty features that are dominantly observed in the L band. We present an example that concerns only the disks encountered around evolved stars. The Aromatic Infrared Bands (AIBs) are observed in very various environments: evolved C-rich stars such as AGB stars, PNs, or evolved massive stars such as late-type Wolf-Rayet stars. Even though no specific molecules have been identified, Polycyclic Aromatic Hydrocarbons (PAHs) are the most probable carriers of the AIBs. The L-band (together with the N band) can be used to study the growth and fate of carbonaceous dust such PAHs. The PAH bands from 7 to 9 micron (CC modes) behave generally in a decoupled way compared to the 3micron and 11-14 micron plateau (out-of-plane C-H stretching modes). In particular importance, are the PAHs discovered around double-chemistry sources, i.e. evolved carbon-rich sources surrounded by an oxygen-rich dusty disk, that is now believed to store the result of previous mass-loss event, when the primary of secondary star was oxygen-rich. The high spectral resolution is of great importance for studying the hottest sources and their environment that can be a disk, but also sometime an expanding nebula in case of outburst (novae), or a colliding-wind pattern for the most massive double source. MATISSE will represent a definitive MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 48 of 64 improvement upon previous studies by providing images in the LMN continua but also in important lines such as Br (4.05m) and from the Pfund series (Pf, Pf, Pf, since these hot sources are also surrounded by an environment rich of plasma, and often dust at larger scale. The disk of plasma emits a copious amount of free-free continuum, and is visible only in the vicinity of the most-often unresolved central star. Thanks to the MATISSE high spectral resolution mode, the study of the inner disk is much easier, since the plasma environment can be isolated from the other flux sources. We note that the goal is to isolate the signal of an emission line from the signal of the nearby continuum. In most cases, the lines should be considered as spectrally unresolved except exceptional cases such as novae or Wolf-Rayet stars exhibiting radiative wind with velocities in the range of 20005000 km/s. Summary: Generally bright targets (typically K/L<4/3), Flux in K dominated by the hot central source, high visibilities for a fringe tracker, Overlap of some scientific aspects with the Herbig Be stars, for stars with dusty disks (B[e]) Sources dominated by interacting binaries, with many potentially complex features (spiral-arms, clumps, jets…) Velocities in emission lines from 200 up to 2000 km/s for erupting or jet-like sources, barely resolved in the L band at the highest resolution (Br, Pf…), Potentially complex chemistry in some cases (binary post-AGB with disks, double-chemistry disks, and symbiotic sources) best studied in the medium resolution mode. The most interesting features are in the L band. 5.3.2 Cool giants and supergiants Cool giants and supergiants (i.e. stars on the AGB and Red Supergiants) have been and still are prime targets for interferometry since they are large, bright and offer interesting science. The main scientific questions relevant for MATISSE concern (a) the structure of convection and the formation of large scale surface inhomogeneities and (b) understanding the mass loss mechanism(s), in particular the role of dynamic processes like pulsation and dust formation. For both topics, time dependent modelling is essential. However, this is still in a very exploratory stage, especially when 2D or 3D models are concerned. In a certain respect the situation is worse than for YSO disks since the morphology is more complex. Therefore model predictions for MATISSE are very limited and only more qualitative statements can be made at the moment. But on the other hand this means that new observations (in particular using the imaging capabilities of MATISSE) are absolutely essential to constrain and improve the modelling. The L band contains a few diagnostic molecular features for studying the above topics: the SiO first overtone bands and the Br emission line near 4m and the C2H2/HCN combination bands near 3.1 and 3.9m. Due to the rather narrow width of Bra few 10km/s) and the weakness of the SiO bands these features require spectral resolutions of a few 1000 to be resolved. On the other hand, the 3.1m feature can already be studied well at spectral resolutions of a few 100. The feature consists of a very large number of rather strong lines, thus even spectral resolutions of several 1000 are not enough to resolve these but the large number of lines produces a notable feature already at low spectral resolutions. The high temperature sensitivity of this feature and the importance of C2H2 as a key building block of amorphous carbon dust make this feature particularly attractive for MATISSE and for the above science cases, also since this is the only C2H2 feature easily observable from the ground. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 49 of 64 The importance of the 3.1m feature as a diagnostic tool for MATISSE observations at a spectral resolution of at least 200 is demonstrated in Fig. 33 (left). It compares the visibilities of two 1D dynamic (i.e. time dependent) models, one which develops a stellar wind driven by pulsation and amorphous carbon dust and a model which develops no wind, i.e. has an atmospheric structure quite similar to a static atmosphere. This comparison also points to the strong temperature dependence of the feature, an aspect relevant for the possible effects of atmospheric inhomogeneities (caused by convection, dust formation or hydrodynamic effects; see below). Figure 35 (left) also compares the visibilities for two pulsational phases of the dynamic model with a wind. Besides an overall change in diameter, the shape of the 3.1m feature changes by several 0.01 in visibility. Figure 36 [Left] Comparison of two dynamic 1D models for C-rich AGB-stars in the L band at a spectral resolution of 200 for three different baselines. Full lines show the dynamic model with a stellar wind at maximum luminosity, dotdashed lines show the same model at minimum luminosity. Note the prominent signatures of the C2H2/HCN combination bands near 3.1 and 3.9m The dotted lines at high visibilities are for a hotter dynamic model not developing a stellar wind. A typical distance of 500pc was assumed for both models. [Right] Comparison of two dynamic 1D models for C-rich AGB-stars in the M band at a spectral resolution of 2000 for three different baselines. Full lines show the dynamic model with a stellar wind at maximum luminosity, the dotted lines are for a hotter dynamic model not developing a stellar wind. Note the signatures of CO fundamental lines. A typical distance of 500pc was assumed for both models. In the M band the main diagnostic features are the CO fundamental lines but their spacing and strength requires spectral resolutions of at least 2000. From exploratory dynamic 1D models for AGB stars we expect differences in the visibilities across CO fundamental lines of the order of 0.05, provided the spectral resolution is larger than 1000 (Figure 36, right). Nevertheless, at lower resolutions the differences between the distribution of gas close to the photosphere and cool material in the upper atmosphere can be studied by comparing images in the NIR and the L/M bands. This is of special relevance for AGB stars with very extended and likely inhomogeneous atmospheres. As an illustration we show in Figure 37 synthetic snap-shot images of a 3D AGB model of Freytag & Höfner in the K and M bands (spectral resolution 1500). The differences in the appearance are obvious. For cool supergiants, ongoing studies indicate that the differences between the NIR and L/M are more subtle in the images but should be more prominent in direct interferometric observables. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 50 of 64 Figure 37 Comparison of a snapshot of a 3D AGB model in the K- and M-bands at a spectral resolution of 1500.In the Kband the intensity ranges between 0 and 30000 erg/s/cm2/Å, in the M-band between 0 and 2000. Summary: Generally bright targets (typically K/L<4/3) Minimum K-band visibilities for fringe tracker 0.05, Klim~6 for the coherent flux. Time dependent models still exploratory, especially in 3D, therefore observations are essential for further constraints/improvement. Two main science cases: Convection/large scale inhomogeneities and dynamic processes (formation of molecules and dust in shells, wind driving mechanisms) L band: very promising at low spectral resolution for carbon stars (strong C2H2/HCN features), for M-stars interesting at highest spectral resolution (Br, SiO). M band: resolution of (at least) 1000-2000 needed to see effects across CO fundamental lines but comparison with NIR should show differences between surface structures of lower and upper atmosphere, especially for AGB stars with extended atmospheres. Doc. Issue Date Page MATISSE Science Analysis Report 5.4 VLT-TRE-MAT-15860-9008 1 01.03.2012 51 of 64 Secondary Science Case: Extrasolar Planets The mid-infrared spectral domain is well adapted to the observation of close-in or young Extrasolar Giant Planets (EGPs). Due to their high effective temperature, these sources are significantly luminous in this wavelength domain. Atmospheric composition, planetary mass, and orbit inclination of extrasolar planets around nearby stars may be studied using the VLTI (Segransan et al. 2000; Lopez et al. 2000; Vannier 2003). Direct characterization of known EGPs is foreseen with the MATISSE instrument by using differential phase and phase closure (Segransan et al. 2000; Vannier et al. 2006). Assuming (i, j) the pair of telescopes i and j, the approximated expression of the differential phase produced by a close-in EGP is: obj,ij ( ) I planet ( ) C* (uij ) I star ( ) sin( 2uij ) Istar(λ) and Iplanet(λ) are the monochromatic flux of the two components, separated by an angular distance ρ. C*(u) is the modulus of the intrinsic visibility of the partly resolved stellar component with uij=Bij/λ the angular frequency (Bij being the baseline ranging between the telescopes i and j). The expression of the phase closure of the planet, denoted as obj ( ) , is: obj ( ) obj,ij ( ) (i , j ) ij I planet ( ) C* (uij ) I star ( ) sin( 2 u ij ) Barman et al. (2001) modelled cool and hot irradiated 1-Jupiter mass and radius EGPs with intrinsic temperatures of 500 K and 1000 K, and various orbital distances. Regarding the atmospheric composition, especially in terms of opacity, two types of atmosphere were considered: a “dusty” atmosphere where all the particles and grains remain in the upper atmosphere, and a “condensed” one where dust has been removed from the upper atmosphere by condensation and gravitational settling. In 2000, a planetary companion identified as Gliese 86b was detected by radial kinematics around the K1 star Gliese 86 (Queloz et al. 2000). This star has an apparent magnitude of about 4 and 3.8 in L and N band, respectively. The planetary companion is close to its parent star, with a 0.11 AU semi-major axis and an angular separation of about 10 mas. It has a minimum mass of about 4 MJ, a rotating period of 15.76 days and a very low eccentricity of 0.04. According to Matter et al (2010), the expected flux ratio between Gliese 86 and its planet is much more favourable in L and N band (≈ 10-3) than in the near-infrared (≈ 10-5) or the visible (≈ 10-6). Matter et al. modelled the differential phase signal of Gliese 86b, as expected in the spectral sensitivity domain of MATISSE. Assuming a mean projected baseline of about 110 m, the expected differential phase signal produced by Gliese 86b is represented in the left panel of Figure 38. In right panel of Figure 38, an example of expected closure phase signal is represented in the case of Gliese 86b; The closed loop of baselines considered here is the UT1-UT3-UT4 triplet; the baseline UT1-UT4 being assumed to be aligned with the separation vector (denoted as ‘ρ’) of the planetary system. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 52 of 64 Figure 39 Left panel: Expected differential phase signal produced by Gliese 86b between 1 and 15 μm of wavelength. Right panel: Expected closure phase signal between 1 and 15 μm. According to this Figure, the amplitude of the phase signal of the planet is greater in N band and of the order of 0.1° (≈ 10-3 rad). Note that the period of the sine modulation increases with respect to wavelength, so that the differential phase is quite linear from 8 μm to 13 μm. Concerning the phase closure, its amplitude also increases with respect to wavelength, attaining almost 0.15° (≈ 3.10-3 rad) in N band. When residual atmospheric piston is removed during data processing, it removes at the same time the linear part of the phase signal. As a result, the remaining expected differential phase signal is the curvature of the curve, with an amplitude for the N band of the order of 0.03° (≈ 5 10-4 rad) in the case of GL86. In L and M bands, the signal amplitude (differential phase and phase closure) decreases by a factor of 10 (≈ 10-4 rad). However these spectral bands seem to be the best compromise between the expected flux ratio between an EGP and its star, and the relatively limited thermal background noise present in this wavelength domain. The overall calibration of other limiting factors on the differential phase, such as the dominant chromatic effects of water vapour in N band, is detailed in Matter et al. (2010). As a conclusion we can state that the requirements, related to the science case of hot Jupiters and according to the GL 86 case, are: Closure phase: ~10-4 rad and ~5.10-4 rad in L and N band, and Differential phase: ~10-4 rad and ~5.10-4 rad in L and N band Several other candidates could be foreseen for MATISSE using differential phase and closure phase observables. Vannier (2003) performed a feasibility study, in terms of fundamental noise in K and N band, on about twenty exoplanet candidates already discovered by radial kinematics. This study was recently extended to phase closure in L and M bands in the science case document of MATISSE, for three peculiarly favourable EGPs candidates: τ boo, 51 Peg , and 55 CnC. Considering Fig.36, we see that the potential SNR in term of fundamental noises on the phase closure for these three candidates could be very favourable in L and M bands. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 53 of 64 Figure 40 Typical noise level on the closure phase for 6h of integration for AMBER, MIDI and MATISSE, taking into account the fundamental noises (detector and photon noises). Overplotted are the flux ratio between the star and planet for three selected examples: Boo, 51 Peg and 55 Cnc. The fundamental limits of the detection in the different bands are represented. In terms of time budget, achieving a precision of about 10-4 radians on the closure phase would require an integration time of about 6h per star, which represents nearly 1 night of observation. In addition to these potential EGPs candidates, the detection of well separated and intrinsically hot EGPs, embedded in their debris disk, could be also foreseen. This is the case of the star beta Pic which would possess a 1500K and 8 MJ planetary companion, detected by Lagrange et al. (2009) at a projected distance of 8 AU (≈ 0.4 arcsec). Since such an angular separation is very well resolved by typical interferometers, the sine modulation is clearly visible in the phase. This would prevent from a strong decreasing of the phase amplitude when residual atmospheric piston is removed. Using a simple blackbody model for Beta Pict b and its A-type parent star, the expected flux ratio is about 9.10-4 at 10 microns. The corresponding signal requirements are about 0.1° (≈ 10-3 rad) and 0.2° (≈ 3.10-3 rad) for the phase closure amplitude in L and N band respectively, and 0.05° (≈ 5.10 -4 rad) and 0.1° (≈10-3 rad) for the differential phase amplitude in L and N band respectively. Note that the blackbody assumption for Beta Pict b is in good accordance with the expected flux derived from a cloudy model from Hubeny and Burrows (2007). This model gives an expected planetary flux of about 1.5 mJy at 10 microns; the corresponding blackbody flux of Beta Pic being approximately 1.5 Jy at 10 microns. According to IRAS, the measured stellar flux is about 3.5 Jy at 12 microns, showing an important infrared excess with respect to a blackbody model. This infrared excess produced by the dusty content of the circumstellar disk represents approximately 60% of the total integrated density flux. This optically thin debris disk, seen edge-on, is characterized for example by an inner part (r<25 AU) depleted by a factor of ~100 with respect to the regions of peak density (Lagage & Pantin, 1994). Several structures have been identified in the disk, including for example a warp at ~ 70 AU studied in detail by Boccaletti et al (2009), or axisymmetric clumpy structures reported by Wahhaj (2003) and located between 15 and 80 AU from the star. These clumps are interpreted for the moment as the projection of rings, which could indicate the presence of planetesimal belts or planetary orbits. However the inner part of the disk (< 13 AU) (including the ‘hot dust’ content, the possible planet already discovered and small-scale asymmetries) still remains quite unknown because of a lack of angular resolution and the use of coronagraphs. This highlights the importance of interferometric MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 54 of 64 observations of the Beta Pic system (and possibly Beta Pic b) in the mid-infrared domain. In 2010, Absil et al. have attempted to detect Beta Pic b using the closure phase observable in K band. Their detection limit would allow brown dwarfs to be detected (K-band contrast ~ 5.10-3) but appeared to be insufficient to detect the planetary companion which presents a K-band contrast of about 2.5.10-4. In this context, L (and N) bands appear anyway to be more advantageous in terms of flux ratio (3 times better) for future observations of Beta Pic b, using closure phase or differential phase. 5.5 Secondary Science Case: Solar System Minor Objects With the angular resolution provided by the VLTI, the direct measurement of the sizes and shapes of the solar system minor bodies, now becomes possible. In particular, the VLTI can spatially resolve asteroids in a range of sizes and heliocentric distances that are not accessible to other techniques such as adaptive optics and radar mapping. The feasibility of interferometric observations of asteroids with the VLTI, has been recently demonstrated with MIDI. This science program was developed in the Phase A Science Case document; it is here updated by new references and by more precise specification of the MATISSE sensitivity requirements. With MIDI and the UTs, fringes have been recorded on two main-belt asteroids, (234) Barbara and (951) Gaspra (Delbo et al. 2009), both having correlated fluxes of about 1 Jy. Delbo et al (2009) measured an extension of about 15 km for (951) Gaspra, in good agreement with the ground truth coming from the in situ measurements by the Galileo mission. Moreover, they derived size information about the shape of (234) Barbara, known to exhibit unusual polarimetric properties. In particular they found evidence of a potential binary or strongly concave nature. This was confirmed by further observations based on stellar occultation. More recently, Matter et al (2010) successfully obtained fringes on a big Main-Belt asteroids, (41) Daphne, using the ATs. Using simultaneous spectrophotometric and interferometric data, they derived size estimates in good agreement with previous direct disk-resolved observations, and they also constrained for the first time the thermal properties of the asteroid, including thermal inertia and surface roughness. MATISSE will be particularly well suited for observations of asteroids in the N band. Temperatures of asteroids are around 450-400K in the near-Earth space (heliocentric distance of about 1 AU) and about 250-200 K in the main belt (at heliocentric distances between 2 and 3.5 AU). The wavelength of the corresponding emission peak is thus in the N band between 7 and 14 µm (M. Delbo, PhD thesis, 2004). MATISSE Performance Figure 41 shows that with a projected flux of limit of 1 Jy in N band, about 1000 asteroids should be observable with MATISSE. This number increase to about 5000, if MATISSE can detect source down to 0.5 Jy, which the MIDI experience suggests is possible. Although the number of asteroids observable is quite large in the case of UTs, it is clear that the main contribution of the VLTI to the studies of asteroids lies in the possibility to observe selected objects of particular interest. The performance goal in terms of sensitivity of MATISSE in the N band opens the door to the possibility of investigating faint and small targets with sizes smaller than 50-40 km in the main belt, i.e. in a diameter range where direct determination of asteroid sizes is at present limited to few bodies explored by spacecraft flybys. Reliable asteroid size estimation requires visibility measurements along several projected baselines. While the process to retrieve such information is slow MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 55 of 64 with MIDI, with MATISSE many visibility measurements will be possible in a short time. Figure 41: Cumulative number of main belt asteroids observable (Visibility > 0.1) with the VLTI in the thermal infrared as function of the limiting flux of the instrument. Diameters of asteroids are calculated from their known absolute magnitudes and assuming a geometric visible albedo equal to 0.11. The visibility is calculated assuming a uniform disk and a baseline of 24m in the N band (and Q band) and a baseline of 16m in the M band. A vertical line is drawn in correspondence with the sensitivity goal of MATISSE in the N band of 1 Jy. VLTI observations of binary asteroids could provide accurate determinations of the elements of their orbit around each other. This leads directly to estimates of the mass of the components. Since the interferometric data also leads to estimates of the sizes of the components, MATISSE observations provide direct estimates of the density of binary asteroids. The densities of course serve as indicators of the composition of the asteroids. The M band capabilities of MATISSE will be of great utility in the case of NEAs (Near Earth Asteroids) which have larger angular sizes than the main-belt asteroids and are typically warmer. The M-band photometric and interferometric data will be complementary to those obtained in N band for the purpose of constraining the asteroid temperature distributions. In M band the Main Belt asteroids should not be with reach of the MATISSE sensitivity and would require sensitivity better tha 0.2 Jy. It is not clear whether the M band could be twice as sensitive as the N band and thus allows one to reach a sensitivity of 0.5 Jy, the M band is part of the Technical Specifications but the instrument is optimized for the L band. Between 10 and 20 NEAs could be observable with MATISSE depending on the limiting correlated flux in the M band. In the case of main belt asteroids, the flux drop of the thermal emission of asteroids in the M band and the increase of spatial resolution is so strong that MATISSE will offer only limited possibilities to observe main belt asteroids in the M band. Moreover, observations of asteroids in the M band is of interest since there is a contribution of solar light reflected by the surface if the object has a high albedo (e.g. albedo > 0.3). In the L band the contribution of the reflected sunlight is strong and the thermal radiation is, in general, so low that no asteroids will be observable in this band. Doc. Issue Date Page MATISSE Science Analysis Report 6 VLT-TRE-MAT-15860-9008 1 01.03.2012 56 of 64 SUMMARY 6.1 Science case requirements Table 12 below summarizes the requirements derived from the science cases studied in this document. Coherent Flux Sensitivity Protoplanetary disks (number of available sources) Protoplanetary disks in N : signatures in visibility and closure phase N ~ 1 Jy UTs ~20 Jy ATs L ~0.2 Jy UTs ~ 4 Jy ATs _ Visibility Accuracy Closure Phase Accuracy Differential Phase Accuracy Imaging & Spectroscopy _ _ _ _ Scenarios 1-2-3-4: 1 - 10 % in N Scenarios 1-2-3-4: 0.05-1 radian in N _ _ Scenarios 5-6: 1 - 5 % in N Scenarios 5-6: 0.02 – 0.1 radian in N _ _ _ Herbig : V/V~.5 in L, .7 in N T Tauri : V/V~.1 in L, .7 in N Asymmetries : V/V~.17 in L down to 0.02 , 0.02 in N Protoplanetary disks in L (&N) _ Protoplanetary disks : interest of the L&M spectral lines Protoplanetary disk (image reconstruction approach) AGN _ _ _ _ Sp. Res. in L&M > 600 Desired Sp. Res. in M > 1300 _ 10 % 0.2 radian _ best with 2 % best with 0.01 radian One test case for N band imaging 10% _ _ _ _ _ _ Sp. Res. in L&M > 200 Interest for L with R ~ 1000 Sp. Res. in M > 1000-2000 _ Evolved Stars Asteroids N ~0.5 Jy UTs L ~0.1Jy UTs Very luminous objects N ~ 1 Jy _ _ _ M < 0.5 Jy L < 0.1 Jy Extrasolar N ~ a few Jy _ ~ 5 10-4 radian in N ~ 5 10-4 radian in N _ planets down to 1 Jy ~ 10-4 radian in L ~ 10-4 radian in L L ~ a few Jy up to 10 Jy Table 12 : A synthetic view of the main requirements derived from the science cases presented in this document. Note, that the empty boxes are not to be filled. One filled box per column and per observable is useful to constrain the requirements. Doc. Issue Date Page MATISSE Science Analysis Report 6.2 VLT-TRE-MAT-15860-9008 1 01.03.2012 57 of 64 Feasibility of science programs Table 13 below summarizes the feasibility of the astrophysical programs here discussed. Coherent Flux Sensitivity Visibility Accuracy Closure Phase Accuracy Differential Phase Accuracy Imaging & Spectroscopy Are the requirements defined here satisfied by the Performance Analysis Report [RD2] calculations ? Protoplanetary Yes _ _ _ _ disks (number of available sources) Protoplanetary _ Yes Yes _ _ disks in N : signatures in visibility and closure phase Herbig : _ Protoplanetary _ _ _ Yes disks in L (&N) Protoplanetary disk (image reconstruction approach) Protoplanetary disks : interest of the L&M spectral lines AGNs Evolved Stars Asteroids _ T Tauri : Yes Asymmetries : Yes, but certain scenarios require high accuracies, V/V < 2% Yes Yes _ _ _ _ _ _ Yes for R in L&M > 600 No for M > 1300 Yes Yes Yes _ _ _ _ _ Yes for R in L&M > 200 Yes for R in L ~ 1000 No for M > 1000-2000 _ _ Yes in N _ _ _ No in L Extrasolar Yes in L and _ Challenging as an Challenging as an _ planets N exploratory goal exploratory goal Table 13 : Feasibility of the astrophysical programs according to the Performance Analysis Report [RD2]. The empty boxes mean that the requirements are not of interest or not commented or not studied. We conclude that the feasibilities, of the selected astrophysical programs considered in this document, are met according to the expected performances of MATISSE (RD2). MATISSE Science Analysis Report 7 Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 58 of 64 VLTI infrastructure: the desired equipments In this section we outline the desired equipments for the VLTI infrastructure. In particular, this concerns: The external fringe tracking The lateral pupil motion monitoring The Tip-Tilt correction The VLTI data content The use of PRIMA with MATISSE We are also working on two other issues, which are : a) the possibility to perform Fourier Transform Spectrometry with MATISSE and b) the possibility to observe in an hybrid mode mixing ATs and UTs beams. The work on these issues is not presented in this document since it is not yet completed and does not provides for the moment the same level of quantitative information, compared to the fringe tracking issue for instance. 7.1 External Fringe tracker The external fringe tracker is very important for MATISSE. This device implemented in the VLTI infrastructure will allow : a) To perform the medium and high spectral resolution modes of MATISSE for L&M bands. b) To access to a significant AGNs and Young Stellar Objects sample by accessing to faint sources. c) To increase the measurement precisions by stabilizing the instrumental transfer function. a) The external fringe tracking is required in order to perform the medium and high spectral resolution modes of MATISSE for L&M bands. The study of the spatial location in the disk of the dust and gas line emission with MATISSE would require resolution ranging from a few tens for N to a few hundred and would require a resolution of several hundred in L&M. A spectral resolution in N ranging from 30 to 220 is required in N for the mineralogy study of dust in protoplanetary disks. Crystallinity was identified to occur in the inner part of disk from MIDI/VLTI observations (van Boekel et al. 2004, Nature 432, 479). R=30 was a resolution sufficient with MIDI to separate spatially the amorphous material from the crystalline signatures. Using TIMMI2 with R = 160 in the N spectral band (van Boekel et al. 2005, A&A 437, 189), it is a mixture of several dust components which is used in the modeling fit of the data. This mixture includes amorphous olivine, amorphous pyroxene, crystalline forsterite, crystalline enstatite, amorphous silicate. PAH emission was also added as a fit component. In the L band part of the spectrum, Geers et al. (2007, A&A 476, 279), did used a spectral resolution of R=600 to study Hydrogen lines emission including Br and the PAHs emission. In the L&M band, at medium and high spectral resolutions, it is essential to use a fringe tracking because with the detector read out speed it is impossible to read all the spectral channels within the coherence time of the atmosphere. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 59 of 64 b) The external fringe tracking is important to access to a significant Young Stellar Objects and AGNs sample by accessing to faint sources. The sensitivity limit [RD2], without fringe tracker and on one individual frame, in the L band is of the order of 0.2 Jy with UTs and 2 Jy with ATs in low resolution and HighSens mode, in the N band it is of the order of 0.7 Jy with UTs and 12 Jy with ATs . With a fringe tracker, a 15 minute observation pushes these limits, in the L band, to the order of 0.003 Jy with UTs and 0.03 Jy with ATs, and in N band, to the order of 0.008 Jy with UTs and 0.13 Jy with ATs. The observation is obtained with a SNR of 3 on the coherent flux for the ensemble of the spectral channels. Based on the ‘circumstellardisks.org’ catalogue (www.circumstellardisks.org), we evaluate that the numbers of observable young stellar sources brightest than the sensitivity levels quoted for L and N band are almost : N band: L band: ATs: ~ 2-4, ATs: ~ 14, UTs: ~ 38 UTs: ~ 44 We have assumed that the object source visibilities V 1. An increase of the sensitivity by a factor of ~ 5 would change the accessible sources to : N band: ATs: ~ 20, UTs: ~ 70 L band: ATs: ~ 40, UTs: ~ 61 In fact the increase of sensitivity is not 5 but of the order of 70-80 on the coherent flux, see the above numbers computed in this section from RD2. This huge increase of sensitivity cannot be easily translated into a number of available targets. First because the circumstellardisks.org catalogue is incomplete for faint magnitudes. Second because it is not easy to answer quantitatively to the question ‘could we fringe track on all the sources’ : on their K band counter part or on a off axis source. For this later question an answer is provided in RD3 in which we present, for several science cases including the Young Stellar Objects, a list of sources with off axis stars on which fringe tracking could be ensured (see Table 6, 7, 8, 9, 10 of RD3 for more details). These off axis star are located within 30-60 arcsecs of distance from the main source. Several subsets could be considered for young stellar objects for instance. A subset with nearby sources located at less than 150 parsec. The motivation of this criterium is the Taurus region. The total number of sources with this criterium is 23. A subset of source at more that 150 parsecs, the subset counts 24 sources. A subset of sources at less than 52 pc of distance. The motivation is the fine study of disk structures. This subset counts 6 sources. A subset of sources composed of T Tauri stars with close companions. This subset counts more than 50 sources. Concerning AGNs, approximately 20 AGN targets are available at the nominal MATISSE performance limits in blind mode. In more details (see the previous AGNs section) in blind tracking mode, we expect to be able to map 10-20 targets in N-band, 4-T mode, and ~20 targets in L-band 4-T mode. If we use L-band fringe sensing to ‘stabilize’ (coherencing and/or post-data processing approach) the N-band fringes, the number of N-band targets becomes equal to the number of L-band targets, i.e. ~20. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 60 of 64 We have also examined the number of targets with bright cores at K-band, or near (<30 arcsec) relatively bright reference K-band stars. The number is of course a strong function of the limiting magnitude of the fringe tracker. The tables below give approximate numbers of southern targets for different K-band limiting magnitudes (derived from the Veron-Cetty, Veron list) and can perhaps be multiplied by 2 for a more complete AGN list. Single Beam Fringe Tracking using the AGN core as reference: K_lim=8 - 1 target (NGC 1068) K_lim=9 - 1 target (same) K_lim=10 - 9 targets K_lim=11 - 30 targets (including above) Dual Beam Tracking using a reference star within 30” K_lim=7 - 3 targets K lim=8 - 5 (including above 3) K_lim=9 - 21 (including above) K lim=10- 40 targets. It may be worthwhile to point out that the single-beam versus dual-beam AGN target lists are (mostly) non-intersecting sets - eg. the ~30 targets on the single-beam list are separate from the ~40 on the dual-beam list. It is thus expected that the use of a fringe tracking allowing K limit between 9-10 will double the sample of studied AGNs. c) The use of an external fringe tracker can allow to increase the measurement precision by stabilizing the instrumental transfer function. We here consider three cases : The OPD jitter of the fringe tracker (as given for FINITO in AD2 for the UTs) is less than 450 nm RMS, The OPD jitter is less than 300 nm RMS as a goal given in the ICD (AD2), The OPD jitter is less than 180 nm RMS as reachable with ATs in the ICD and as a goal for the improvement of the UTs vibration. This jitter of 180 nm RMS corresponds to a reasonable contrast loss of 5 %. If we assume the observation of a L band flux source of 3 Jy, with the current performance of OPD jitter given in the ICD, the performances of MATISSE allow (RD2) : L band 3 Jy AT with FT OPD Jitter=150 nm RMS UT no FT UT with FT OPD Jitter=450 nm RMS Accuracy for a 15 mn observation with chopping v/V = 10% = 100mrd v/V = 2.3% = 25mrd v/V = 0.8% = 8.5mrd Precision Error V = 10% Error = 100 mrd Error V = 3.7% Error = 32 mrd Error V = 2.6% Error = 22 mrd The accuracy is related to the fundamental noise contributions (detector, photon noises from MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 61 of 64 the source and the background). The precision involves the calibration procedure (cycle source/calibrator) and in subject to change in the transfer function. In the previous table the case AT with FT, the result is dominated by the fundamental noises, it is why the accuracy and the precision are almost the same. In the case of the N band (non represented in the Table), the Fringe Tracker allows to gain a factor of about 1.5-2 on the accuracy of the closure phase thanks to a gain on the fringe contrast. In the case of high flux source and in N band, the contribution of the variation of the transfer function compared to the fundamental noise becomes to be preponderant. The fringe tracking allow in this case to stabilize the transfer function and allow to gain not only on the closure phase accuracy but also on the visibility precision by a factor of about 2. These gains are seen as important. The gain in accuracy in the L&M band shown in the Table are stronger than those in N band. To illustrate the impact of the performance of a fringe tracker in OPD stabilization, let us evaluate for the L band the effect of the OPD jitter on the precision of the visibility : Fringe Tracker Contrast loss Resulting visibility Equivalent UTs Equivalent ATs OPD Jitter precision source brightness* source brightness 450 nm RMS 28 % 2% 0.07 Jy 0.9 Jy 300 nm RMS 14 % 1% 0.14 Jy 1.8 Jy 180 nm RMS 5% 0.35 % 0.4 Jy 5 Jy * Brightness of the source for which the fundamental noise give a visibility accuracy equivalent to the precision. The strongest precision on the resulting visibility are reached when the OPD Jitter for the Fringe tracker is reaching 180 nm RMS. Going down 180 nm RMS for the Fringe Tracking stability is of importance since for example, the visibility precision of a > 5 Jy source tends towards 0.35 %. Several science cases will strongly benefit of such high level of precision in the calibrated visibility. It is the case of the detection of low brightness asymmetries in protoplanetary disks down to less than 1% of the total source flux. These asymmetries are important signatures to search for since linked to the planet embryos or to the dynamic interaction between the planets and the disk. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 62 of 64 Characteristics and requirements of the external fringe tracker We here define the characteristics and requirements for the external fringe tracker. Number of telescopes: 4 telescopes Fringe tracking in K (instead of H). It is due to the observation of the AGNs and on the stars embedded in dust envelopes. Chopping compatibility: Full fringe reacquisition in less than 30ms (full including guiding: MACAO or STRAP, vibration damping …). Goal: less than 10ms for closing FT loop at K=10. Off axis tracking allowed within 30-60 arcsecs. Sensitivity and tracking accuracy. - Tracking limit magnitudes compatible with the extragalactic program (K=12). Possibility to fringe track on a quasar observable in L like 3C273 (K 9.7, 0.5 Jy in L band). The specification is K>10, with a goal K>12. - Tracking accuracy: To achieve a budget of 5% contrast loss in L, compatible with all the other contributions of contrast loss (RD2), the requirement is p 180nm RMS over 1 minute. This requirement should be valid up to K=8-9. Residual data recording : The fringe sensor residual data must be part of the MATISSE pipeline data in order to perform off-line processing and to improve the measurement accuracy of MATISSE. Pupil lateral motion monitoring as part of the fringe sensing device. It is possible that the 2sd generation fringe tracking device requires for its own operation a monitoring of the lateral pupil motion. In such case it will be important (see below) for MATISSE to collect the pupil monitoring data. 7.2 Tip-Tilt correction with IRIS IRIS can monitor the tip tilt inside the laboratory. A correction at low frequency is made by the VLTI The residual values of these corrections are given in AD2. In AD2 also are given the possible performance of tip-tilt with the IRIS fast guiding IFG. The use if the IFG requires having fast actuators inside the instrument. Considering the weak gain provided by IFG, no fast corrections will be made (in RD2 the performance is calculated without IFG). We would like to record the Tip-Tilt residual values in order to flag the bad frame at the time of data processing (RD4). In the case of IRIS use : the pupil lateral position can be checked. However this must be seen as an occasional check performed at each acquisition of the star or of the calibrator. A more frequent check is desirable but a highest priority is given to the control of the slow tip-tilt motion and correction. 7.3 Lateral pupil motion monitoring While real-time lateral pupil stabilization is not required (RD2), lateral pupil motion monitoring is required. MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 63 of 64 In the Performance Analysis Report, Table 9.5.5, ‘Contribution of the pupil motion to the contrast loss’, it is shown that the contrast loss due to the pupil shift (mean value) is less than 1 % for 90 % of the time. More precisely, 1 % of contrast loss is produced for a pupil shift of 2.65 mm in L band and 2.3 mm in N band. This shift occurs 2.2% of the time for UTs in L band, 7.1 % of the time for ATs in L band, 2.4 % of the time for UTs in N band and 9.6 % of the time for ATs in N band. Even if the contrast loss produced by a pupil shift is not frequent, it may occur on the calibration star while not occurring on the source. In this case, this contrast loss impacts on the calibrated visibility accuracy. The monitoring during observations of the pupil lateral motion will be used to flag the bad data (RD4) and to ensure ‘calibrability’ of the instrumental transfer function based on comparison of source and calibrator data. 7.4 VLTI data content The VLTI data: Fringe tracking residuals, lateral pupil motion and Tip-Tilt residuals are required for the data reduction process of MATISSE (RD4). Accurate calibration of the instrument transfer function can only be achieved after analysis of the monitored tip-tilt and fringe tracking residuals and lateral pupil motion. Data lying outside valid threshholds will be flagged. It might be worth to record also if possible the Strehl ratios as measured for each IRIS individual frame. 7.5 Use of PRIMA with MATISSE We have difficulty reaching a definitive conclusion on the interest and need of PRIMA facility for MATISSE. This difficulty is partly linked to the fact that the PRIMA off axis fringe tracking and the PRIMA reference modes are planned for the moment only to operate with 2T while MATISSE is a 4T beam combiner. It has been concluded at the end of MATISSE Phase A, in ‘MATISSE Phase A Complement to the Science Case Document, Answer to AI2 and AI3 of the Phase A Board Report, Contribution to the Answer to AI1 – VLT-TRE-MAT-15860-4336’, that: c) The PRIMA off axis facility is of relevance for MATISSE for accessing more sources belonging in particular to the AGN sample which possess approximately 15 sources with a reference star at less than 30 arcsecs of separation, d) The PRIMA phase reference mode facility could significantly improve the image reconstruction quality in relation with the object angular extension and flux. However: e) Considering that the PRIMA off axis fringe tracking and the PRIMA reference modes can for the moment only operate with 2T. f) Concerning the PRIMA off axis fringe tracking facility, the MATISSE requirements would be to have a fringe tracking sensitive to magnitude 10- goal 12 in K. This requirement is for us part of the requirements for the second generation Fringe Tracker. g) Concerning the PRIMA phase reference mode facility, although it can significantly improve the image reconstruction quality, the PRIMA performance in Phase Referencing mode would MATISSE Science Analysis Report Doc. Issue Date Page VLT-TRE-MAT-15860-9008 1 01.03.2012 64 of 64 not be tested before 2012. We do not know what would be the impact to request for this mode which would imply a metrology between the VLTI and MATISSE. As a preliminary conclusion regarding the use of PRIMA in phase reference mode, it is not clear to us how the science benefit of PRIMA for MATISSE balance with any extra cost of study, manpower and time at ESO side and at the MATISSE Consortium side that we are not in a position to insure. APPENDIX (1): Abbreviations and Acronyms AT BCD ESO FDR IRIS MATISSE OPD PDR RMS RON TBC TBD UT VLT VLTI Auxiliary Telescopes Beam Commuting Device European Southern Observatory Final Design Review InfraRed Image Sensor Multi AperTure mid Infrared SpectroScopic Experiment Optical Path Difference Preliminary Design Review Root Mean Square Read Out Noise To Be Clarified To Be Defined Unit Telescopes Very Large Telescope Very Large Telescope Interferometer End of document
