Chapter 12
MIRI Medium Resolution (Integral Field Unit) Spectroscopy
In this chapter…
12.1 Introduction
The MIRI Medium Resolution (Integral Field Unit) Spectroscopy template/mode is to be used
for all observations using the medium resolution spectroscopy mode of MIRI. The mode will be
useful for fields with faint lines and strong continuum, spectra that are rich in spectral lines (such
as molecular band features) and fields with fast moving gas or stars. The parameters described in
this section are used to specify the Observations for MIRI Medium Resolution Spectroscopy.
This spectrograph uses four IFU image slicers to simultaneously produce dispersed images of the
sky onto two detectors (which will be called the SHORT and LONG detectors). Each IFU
covers a separate spectral window. The spectral window of each IFU channel is covered using
three separate sets of gratings (which will be selected by specifying SHORT, MEDIUM and
LONG wavelength ranges). More complete descriptions of the detector readout parameters,
filters/dispersers, detector characteristics, etc. are available in the MIRI Instrument Handbook.
The following fields are defined in Chapter 5: Observation Number (5.1), Observation Label
(5.2), Observation Comments (5.3), Target Name (5.4), Observation-Level Special Requirements
(5.5), and On Hold Comments (5.6), and will not be discussed in this Chapter.
The MIRI Medium Resolution Spectroscopy template [MIR0073] consists of the following
parameters:
Field
Dither Pattern [MIR0268]
Details
select Dither pattern
Acquisition Target Name
[MIR0270]
select Target Name
(if offset target)
Target Acquisition Filter
[MIR0271]
Wavelength Region
[MIR0272]
Readout Pattern
select filter name
select region
select readout pattern
1
Values
choose from list
[MIR0074]
choose from list
[MIR0076]
Notes
see Table 12.1
choose from list
[MIR0077]
choose from list
[MIR0078]
choose from list
see Table 12-2
see Table 12-3
[MIR0437]
Number of Groups
[MIR0439]
Number of Integrations
[MIR0441]
Number of Groups Long
[MIR0462]
Number of Groups Short
[MIR0464]
Number of Integrations Long
[MIR0466]
Number of Integrations
Short [MIR0468]
[MIR03438]
specify number of
groups
number [MIR0440]
specify number of
integrations
specify number of
groups on the long
wavelength detector
specify number of
groups on the short
wavelength detector
Specify the number
of integrations on the
long wavelength
detector
specify number of
integrations on the
short wavelength
detector
number [MIR0442]
number [MIR0463]
number [MIR0465]
number [MIR0467]
number [MIR0469]
Note that ALL parameters listed below are required as part of your
Phase I submission.
.
12.2 MIRI Medium Resolution (Integral Field Unit) Spectroscopy
The following parameters are used to define MIRI Medium Resolution (Integral Field Unit)
Spectroscopy observations.
12.2.1Dither Pattern
Most observations with JWST will require dithering. Select the DITHER PATTERN
[DITHER PATTERN] from those listed in Table 13-2 Dither Patterns Available for MIRI
Medium Resolution Spectroscopy. Note that the dither pattern does NOT apply to the target
acquisition image. While for most observations dithering will be necessary, there are some types
of observations (e.g. planetary transits) for which dithering is not desired. If you are planning an
observation of this type, you should select the "No dither should be taken for this observation"
checkbox to confirm that you really do not want dithering. [MIR0436].
Table 13-2 Dither Patterns Available for MIRI Medium Resolution Spectroscopy
Dither Pattern
Description1
2
dither1-TBD
dither2-TBD
dither3-TBD
1 see
short description1
short description2
short description3
[MIR0080]
[MIR0081]
[MIR0082]
Chapter 8 for details
12.2.2 Target Acquisition
The following parameters are used to define MIRI Target Acquisition observations. Note that for
Medium Resolution Spectroscopy, the science target is generally used for the acquisition,
[MIR0274], although when necessary, an offset star may be used. [MIR0275].
12.2.2.1 Acquisition Target Name
If an offset star is to be used for the target acquisition observation, select the ACQUISITION
TARGET NAME [TACQ TARGET] from the list of targets previously entered (see Section
5.8) [MIR0087].
Note: For APT, the ACQUISITION TARGET NAME field should always be present, but should
be defaulted to the prime target for the Observation. [MIR0088]. The ACQUISITION
TARGET FLUX (TACQ FLUX) [MIR0276] value will be populated by APT based on the
ACQUISITION TARGET NAME [MIR0277] (the flux value is part of the target definition).
Note for developers: If the acquisition target is different than the science target, APT should
provide a warning if the ACQ and Science targets are too far apart [MIR0436]. The warning is
based on the TBR GS Visit splitting distance, but it should not be strongly tied to that value in
case we change out thinking about it.
12.2.2.2 Target Acquisition Filter
Select the name of the TARGET ACQUISITION FILTER [TACQ FILTER] (see Table 12-2)
you wish to use for target acquisition.
Table 12-1 Filters Available for MIRI Target Acquisition
Filter Bandpass (m)
Comment
F560W
F1000W
Center Wavelength 0
(m)
5.6
10
1.2
2
F1500W
15
3
broad band
Silicate, broad
band
broad band
Acq. Filter
3
[MIR0089]
[MIR0090]
[MIR0091]
FND
13
[MIR0092]
10
12.2.3 Science Observation
The following parameters are used to define MIRI science observations.
For developers: there is only 1 exposure allowed in an observation [MIR0470].
12.2.3.1
Wavelength Region
Each of the four IFU image slicers covers a separate wavelength range. Each of these wavelength
ranges can be covered by a set of three available gratings. You can request one or all three
gratings by means of the WAVELENGTH parameter. Note the same wavelength region will be
obtained with each IFU channel. So if you specify SHORT then the SHORT portion of the
wavelength region will be obtained simultaneously with each IFU channel.
WAVELENGTH [WAVELENGTH_1_4,WAVELENGTH_2_3] = ALL
[MIR0093] (default) [MIR0336], SHORT [MIR0094], MEDIUM [MIR0095],
LONG [MIR0096]
Select the wavelength region (see Table 12-3) you wish to use for your science observations; if
you select ALL, data will be obtained in all 3 positions.
Table 12-2 Wavelength Regions Available for MIRI Medium Resolution Spectroscopy
Wavelength Region
SHORT
MEDIUM
LONG
Wavelength Ranges (m)
4.87-5.82
7.45-8.90
5.62-6.73
8.61-10.28
6.49-7.76
9.94-11.87
11.47-13.67
13.25-15.80
15.30-18.24
17.54-21.10
20.44-24.72
23.84-28.82
Note for developer: APT will populate the WAVELENGTH value into both
WAVELENGTH_1_4 and WAVELENGTH_2_3 [MIR0471].
12.2.3.2 Readout Pattern
READOUT PATTERN [READOUT PATTERN] = FAST [MIR0444], SLOW
[MIR0445], FASTGRPAVG [MIR0446], FASTINTAVG [MIR0447]
This field specifies the readout pattern to be used to obtain the data. FAST is used for bright
targets and long wavelength imaging, SLOW is used for faint targets, deep imaging, and MRS
4
spectroscopy, FASTGRPAVG and FASTINTAVG are used for bright targets and to decrease
the data rate.
There are two detectors. The light from the two short wavelength IFUs (Channels 1 and 2) is
dispersed to the SHORT detector and the light from the other two IFUs is dispersed to the LONG
detector. While the exposure time must be the same for the SHORT and LONG detectors, the
NUMBER OF GROUPS and NUMBER OF INTEGRATIONS can differ. Therefore the
parameters for groups and integrations must conform to the following restriction:
NUMBER OF INTEGRATIONS (LONG) * NUMBER OF GROUPS (LONG) =
NUMBER OF INTEGRATIONS(SHORT) * NUMBER OF GROUPS( SHORT)
[MIR0293]
12.2.3.3 Number of Groups
NUMBER OF GROUPS LONG [NGROUPSLONG] specifies the number of groups in an
integration on the long wavelength detector [MIR0496].
NUMBER OF GROUPS SHORT [NGROUPSSHORT] specifies the number of groups in an
integration on the short wavelength detector [MIR0497].
If READOUT PATTERN = FASTGRPAVG, then the number of groups should be greater
than 16 [MIR0492] and a multiple of 4 [MIR0493]. If READOUT PATTERN =
FASTINTAVG, then the number of groups should be 1 [MIR0494].
12.2.3.4 Number of Integrations
NUMBER OF INTEGRATIONS LONG [NINTSLONG] field specifies the number of times
the integration is repeated on the long wavelength detector [MIR0498].
NUMBER OF INTEGRATIONS SHORT [NINTSSHORT] field specifies the number of
times the integration is repeated on the short wavelength detector [MIR0499].
If READOUT PATTERN = FASTINTAVG, then the number of integrations should be a
multiple of 4 [MIR0495].
Note that the following parameters have only one option, and are therefore not included in the
template:
Parameter
Detector Readout Region (Subarray)
Aperture
Value
FULL
TBD
5
6