PH700
Professor Michael Smith
1
Molecular hydrogen in molecular clouds
Shock waves are observed in many locations in the Universe: they are almost
ubiquitous. They represent the impact of gas moving at supersonic speeds. When
one of the components is molecular, strong infrared emission may result. In
particular, strong emission lines of molecular hydrogen in the near infrared are
found. Although the emission lines can be modeled, it is not clear how robust the
interpretations are. This will be of great importance in the coming years, with the
next generation (James Webb) Space Telescope planning to carry several narrow
filters at the wavelengths of molecular hydrogen lines.
The first object of this project is to take a FORTRAN code for constant
temperature clouds of gas and generate a MATLAB version. If possible, update
this code using CLOUDY parameters to then make predictions for individual line
fluxes.
A step-by-step process will be undertaken which can be terminated at any stage
according to time constraints. First, the code for a cloud of molecular gas will be
written, and the nature of the molecular hydrogen emission understood. Then,
cooling and heating functions can be added to produce a radiative shock. Finally,
the strengths of molecular lines can be predicted by adding appropriate formula.
Predictions for near infrared and mid infrared wave bands observed from ground
and space based telescopes may then be employed to construct infrared colourcolour diagrams. These can be used by observers to help distinguish shock waves
from faint stars. A further goal is to construct the shock wave equivalent of the
‘Cloudy’ astrophysical photoionisation code.
Learning outcomes: ability to understand and review scientific literature. Ability
to manipulate and exploit astronomical computer codes. An understanding of
astrophysical hydrodynamics and supersonic flow. An understanding of infrared
astronomy.
1. H2 – what can it tell us about star formation? i.e. where does the emission
come from? What type of gas?
2. Therefore: why try to measure it with JWST and E-ELT ?
3. How bright should it be, how compact might it be? Develop a model which
takes a slab of gas at temperature T, density n(h2), volume V, and
calculated the flux.
4. Look at improving this code by employing better H2 physics
5. Make a comparison to available data for various objects.
6. Start to build a shock wave model to do the same in terms of the shock
speed, shock area, and the upstream conditions.
3. Abstracts/reviews
This is not an easy subject to review! There are a couple of reviews…
George Field 1966
Shull and Beckwith 1982
http://adsabs.harvard.edu/abs/1982ARA%26A..20..163S
…since then…not much, so it needs synthesizing.
PH700
Professor Michael Smith
2
4. We observe H2 directly in several ways:
After excitation in collisions, it may radiate as the vibe-rotational energy
level falls back down.
After excitation by far ultraviolet, into an ‘electronicically excited state
(a continuum) , it cacades back down and through vibe/rote levels,
radiating.
After formation in an (electronically) excited state, it cascades down.
As foreground gas to a hot star, UV absorbtion lines can be detected as
the cold H2 gas absorbs photons, re-radiaitng it isotropically in various
lines.
We infer H2 indirectly, by detecting CO or other molecules which radiate
at around 10K, and assume CO/H2 abundance ratio of around 0.0001.
The trouble is H2 has no dipole moment (it is a symmetric molecule), so
it doesn’t radiate like CO when cold. We observe it only when really
excited or strongly heated: rotationally (few hundred K needed) or
vibrationally (1000K needed at least).
5. What do we observe?
Very bright regions – hot and dense – conditions for collisional
excitation (e.g. shock waves).
Extended diffuse patches/ cloud edges near bright UV sources.
5. What do we observe?
Very bright regions – hot and dense – conditions for collisional
excitation (e.g. shock waves).
Extended diffuse patches/ cloud edges near bright UV sources.
6. Can we illustrate these regions?
Take rho Oph?
Orion OMC-1? What can we show with image manipulation?
Optical: Orion Nebula
2MASS: K and J bands: subtract/divide to show features? Orion Bar:
PDR (UV). OMC-1 shock. Use JHK RGB color image. Will shocks
appear as different colour to UV-excited region?
Rho Ophiuchus. Use HH313 to find the 2mass images. …similoat
structures to orion.
PH700
Professor Michael Smith
3
Young Stars Swim in Pools of Molecular
Hydrogen
http://www.gemini.edu/index.php?option=content&task=view&id=235
Wednesday, 27 June 2007
Figure 1: The spectrum of ECHA J0843.3-7905 divided by that of RECX12 with the fit to the
H2 1-0 S(1) line and residuals in the lower panel.
During a search for hydrogen emission in the disks of young stars, Suzanne
K. Ramsay Howat (UK Astronomy Technology Centre) and Jane S.
Greaves (University of St. Andrews) have discovered a massive layer of
hot gas around a low-mass M3-type star in the 6 million-year-old Eta
Chamaeleontis cluster. Both the strength and the kinematics of the
emission imply that it arises from a disk illuminated by ultraviolet
radiation produced by the central star.
Studying the gas content of protoplanetary disks around young stars is an
important step in understanding the formation of planetary systems.
Molecular hydrogen is one of the main constituents of the atmospheres of
giant planets and so must be present in the disks for Jupiter-like planets to
form. Moreover, the near-infrared emission from it is one of the best
indicators of warm gas that may exist in gaps carved by massive new
protoplanets. This emission may arise from excitation of gas molecules by
a passing shock wave, or by the absorption of ultraviolet radiation (or xrays) from the stars at the center of the disks.
Molecular hydrogen emission was detected from only one of the seven
sources observed by Ramsay Howat and Greaves. The researchers used
PHOENIX, the high-resolution infrared spectrograph on the Gemini South
Telescope at Cerro Pachón, Chile to make the observations. This
instrument was built by a National Optical Astronomy Observatory
(NOAO) team led by Ken Hinkle and is on loan to Gemini from NOAO.
Detecting molecular hydrogen emission associated with disks has proven
challenging, even with 8- to 10-meter class telescopes and advanced
instruments. In fact, this measurement by Ramsay Howat and Greaves is
one of very few published detections of this type of emission. Another
definite detection was recently made around the star AB Aurigae by a team
led by Marty Bitner using the very high-resolution mid-infrared
spectrograph TEXES on Gemini North.
PH700
Professor Michael Smith
4
The mass of hot molecular gas inferred around this source, named ECHA
J0843.4-7905, is about 0.03 solar mass. This is similar to the mass of the
minimum solar nebula. From the shape and width of the line profile
(Figure 1) the authors conclude that this circumstellar gas is orbiting at 2
AU (astronomical units) from the star. Since the system is ~6 million years
old, these results indicate that a significant gas reservoir persists to the age
when gas giant planets are presumed to form. Current theories show that
Jupiter-like object should form in the first ~2 million years of a disk’s life
with the thick atmosphere accreted onto the planet in around 5million
years.
More details can be found in the article “Molecular Hydrogen Emission
from Disks in the Eta Chamaeleontis Cluster”, by S. K. Ramsay Howat and
J. S. Greaves, The Monthly Notices of the Royal Astronomical Society,
2007 in press.
panel.
Figure 1: The spectrum of ECHA J0843.3-7905 divided by that of RECX12 with the fit to the
H2 1-0 S(1) line and residuals in the
PH700
Professor Michael Smith
5
James Webb Space Telescope
http://ircamera.as.arizona.edu/nircam/
NIRCam Design Features
lambda lambda
Bandpass Location Transmission Use
1
2
Name
Center
F070W
0.7000 0.6125 0.7875 0.1750
SW-Filt 0.85
General purpose
F090W
0.9000 0.7875 1.0125 0.2250
SW-Filt 0.85
General purpose
F115W
1.1500 1.0063 1.2938 0.2875
SW-Filt 0.85
General purpose
F150W
1.5000 1.3125 1.6875 0.3750
SW-Filt 0.85
General purpose
No NIRCam
DHS Blocking
Req
F150W2 1.5000 1.0000 2.0000 1.0000
SW-Filt
F200W
2.0000 1.7500 2.2500 0.5000
SW-Filt 0.85
General purpose
F277W
2.7700 2.4238 3.1163 0.6925
LW-Filt 0.85
General purpose
F322W2 3.2200 2.4150 4.0250 1.6100
LW-Filt 0.85
Background Min.
F356W
3.5600 3.1150 4.0050 0.8900
LW-Filt 0.85
General purpose
F444W
4.4400 3.8850 4.9950 1.1100
LW-Filt 0.85
General purpose
F140M
1.4000 1.3300 1.4700 0.1400
SW-Filt 0.7
cool stars, steam
F162M
1.6200 1.5500 1.7010 0.1510
SW-Pup 0.7
cool stars, off-band for
steam
F182M
1.8200 1.7290 1.9500 0.2210
SW-Filt 0.7
cool stars, steam
F210M
2.1000 1.9950 2.2050 0.2100
SW-Filt 0.7
methane
F250M
2.5000 2.4167 2.5833 0.1667
LW-Filt 0.7
methane
F300M
3.0000 2.8500 3.1500 0.3000
LW-Filt 0.7
water ice
F335M
F360M
3.3500 3.1825 3.5175 0.3350
3.6000 3.4200 3.7800 0.3600
LW-Filt 0.7
LW-Filt 0.7
PAH
Brown dwarfs,planets
F410M
4.1000 3.8950 4.3050 0.4100
LW-Filt 0.7
Brown dwarfs,planets
F430M
4.3000 4.2000 4.4000 0.2000
LW-Filt 0.7
carbon dioxide
F460M
4.6000 4.5000 4.7000 0.2000
LW-Filt 0.7
CO
F480M
4.8000 4.6000 5.0000 0.4000
LW-Filt 0.7
Brown dwarfs,planets
F164N
1.6440 1.6358 1.6522 0.0164
SW-Pup 0.6
[FeII]
PH700
Professor Michael Smith
6
F187N
1.8756 1.8662 1.8850 0.0188
SW-Filt 0.6
P-alpha
F212N
2.1218 2.1112 2.1324 0.0212
SW-Filt 0.6
Molecular hydrogen
F225N
2.2477 2.2365 2.2589 0.0225
SW-Pup 0.6
Molecular hydrogen
F323N
3.2350 3.2188 3.2512 0.0324
LW-Pup 0.6
Molecular hydrogen
F405N
4.0523 4.0320 4.0725 0.0405
LW-Pup 0.6
Br-alpha
F418N
4.1813 4.1604 4.2022 0.0418
LW-Pup 0.6
Molecular hydrogen
F466N
4.6560 4.6327 4.6793 0.0466
LW-Pup 0.6
CO
F470N
4.7050 4.6815 4.7285 0.0471
LW-Pup 0.6
Molecular hydrogen
E-ELT Science:
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Dear Colleague,
We would like to kindly solicit your help on the E-ELT project.
The European Extremely Large Telescope (http://www.eso.org/sci/
facilities/eelt/ ) is in its detailed design phase. As part of this
phase, we are preparing a Design Reference Science Plan (DRSP).
PH700
Professor Michael Smith
7
> The DRSP is a collection of science cases provided directly by the
> future users of the E-ELT. The DRSP aims at exploring the full
> range of science cases for which the E-ELT will be used.
> Ultimately, it will help to define the boundaries of the parameter
> space over which the E-ELT will operate. It will be used to guide
> the performance optimisation of the telescope, the prioritisation
> of the instruments, as well as to plan the science operations
modes.
>
> In order for the E-ELT to be a success and to optimally serve its
> community, we need your feedback.
> Please visit http://www.eso.org/sci/facilities/eelt/science/drsp/
> and submit a science case.
>
> To help you assessing the expected performance on the E-ELT, we
> provided two exposure time calculators, as well as a collection of
> technical data, at the above URL (under 'Design Reference Mission'
> in the menu on the right hand side). If you require further help,
> please feel free to contact us.
>
> We are looking forward to your input, and thank you already for
> helping us making the E-ELT a success.
>
> Markus Kissler-Patig (E-ELT Project Scientist)
> on behalf of the project