Step-by-Step APT Guide for NIRSpec IFU and MIRI MRS Observations of Cassiopeia A
Instructions are provided for filling out the JWST APT observing template for the MIRI MRS and NIRSpec IFU Observations of Cassiopeia A example science program, where MIRI MRS and the NIRSpec IFU are used to obtain medium resolution spectra of knots in the Cassiopeia A supernova remnant.
The Astronomer's Proposal Tool (APT) is used for submitting JWST proposals. There are multiple components to an APT submission: generic proposal information, target information, and exposure specifications for the proposed program. This guide discusses how to fill out the APT observing template for the MIRI MRS and NIRSpec IFU Observations of Cassiopeia A example science program.
A filled out APT file can be accessed via the menu options File → JWST Example Science Proposals → Multi-Inst → 26 MIRI MRS & NIRSpec IFU Observations of Cas A in APT. The APT file was created with version 27.3. There may be inconsistencies or additional warnings or errors with other versions of APT.
Please note that APT throws an error about large data volume: at the time that the program was created, the data volume limit was not breached. Subsequent updates to the APT model resulted in changes in how data volume is accounted, causing the estimate for this program to now exceed the limit. The exposure parameters will be updated in a future version of this program, subsequent to the cycle 1 deadline when updates to JDox are permitted. If this was a real program, it would be required to change the exposure parameters to remove this error prior to submission. When possible, we intend to reduce the number of groups for the MIRI simultaneous imaging in the APT file, in order to eliminate this error in APT.
This APT walk-through has value for illustrating how to populate an APT file for this example science case once the exposure parameters are known.
Fill Out Proposal Information
Main article: JWST Astronomers Proposal Tool overview
After opening APT, we selected New JWST Proposal under the New Document pull-down menu just above the tree editor at the bottom-left of the top tool bar. On the active GUI window for the Proposal Information entry in the tree editor, we entered Title, Abstract, and Category of the proposal and kept Cycle number at its default value.
Enter proposed Targets
Main article: APT Targets
Target information is entered in the active GUI window by selecting on Targets in the tree editor. In this active GUI window, we clicked on the New Fixed Target button. We entered STRONG21MICRON-MRS in the field for Name in the Proposal, and selected Unidentified for Category. We entered the coordinates for this source: RA = 23 23 36.1120, Dec = +58 50 10.81. Near the Description field, we clicked the "+/-" button, which opens a list of approved keywords and selected Infrared sources. This source is the one we call FMK 1. We did the same for the other targets, FMK2-MRS and FMK3-MRS, assigning them the coordinates RA = 23 23 29.1050, Dec = +58 50 26.71 and RA = 23 23 27.3400, Dec = +58 50 35.67, respectively. These 3 sources were identified (and their coordinates found) by comparison of Figure 1 from Hurford & Fesen (1996) to WISE and Spitzer-IRAC 8 μm images.
A separate target was created as the position for the MRS dedicated background. We gave it the name CAS-A-BACKGROUND and the coordinates RA = 23 23 42.6778, Dec = +58 51 29.06. After adding the background position, we went back to the entries for STRONG21MICRON-MRS, FMK2-MRS, and FMK3-MRS, expanded the Background Target field, clicked the checkbox beside Observations of this target require companion background observation(s), and in the Target selection field, checked 7 CAS-A-BACKGROUND.
For both NIRSpec IFU and MRS observations, target groups were created. A target group is a group of targets that will be observed the same way, and by observing them as a group, overheads can be reduced such that observing the target group takes less program time overall than observing the targets separately. In the active GUI window for Targets, we clicked the New Target Group button. For the MRS target group, we gave it the Name of STRONG-FMK2-FMK3. In the Target selection field, we clicked the +/- button and added numbers 1, 3, and 6, corresponding to STRONG21MICRON-MRS, FMK2-MRS, and FMK3-MRS. For the NIRSpec IFU target group, we gave it the Name of FMK2-FMK3. In the Target selection field, we clicked the +/- button and added numbers 9 and 10, corresponding to FMK2-NIRSPEC and FMK3-NIRSPEC, respectively.
Main article: APT Observations
In the active GUI window for the Observations entry in the tree editor, we clicked on the New Observation Folder button to specify the observing parameters for our program. In the Label field, we entered MRS Target Group. Note that while this label is not required, setting it is useful for visually organizing your observation folders in the tree editor when potentially many targets and/or instrument setups are used. We then clicked MRS Target Group in the tree editor to open the observation template to be filled out. In the Instrument pull-down menu in the active GUI window, we selected MIRI, and then we selected the MIRI Medium Resolution Spectroscopy template in the Template pull-down parameters. In the Target pull-down parameters, we selected the target group we defined above, STRONG-FMK2-FMK3.
We did the same for the dedicated background for the MRS, giving it a Label of MRS Background, and assigning it a fixed target of CAS-A-BACKGROUND.
In addition, we created NIRSpec IFU observations for the 3 FMKs. Within the previously-created Observation Folder in the tree editor, for the NIRSpec IFU observation of FMK1, we clicked the drop-down parameters at the upper-left of the APT where it says New (just above the tree editor, at the bottom-left of the top tool bar), selecting New Observation. We selected NIRSPEC from the Instrument pull-down parameters in the active GUI window, then we selected NIRSpec IFU Spectroscopy from the Template pull-down parameters. In the Target pull-down parameters, we selected STRONG21MICRON-NIRSPEC. We did the same for the NIRSpec target group, but we chose FMK2-FMK3 in the Target pull-down parameters for this observation.
We did the same for the dedicated backgrounds for the NIRSpec IFU, giving one a Label of NIRSpec IFU - Background, 11 groups for the background to be used for the NIRSpec IFU observation of FMK1, and giving the other a Label of NIRSpec IFU - Background, 7 groups for the background to be used for the NIRSpec IFU observations of FMK2 and FMK3.
Complete APT observation template for MIRI-MRS
As discussed in the parent article and the Step-by-Step ETC Guide, a set of observations will be taken using all 3 grating settings for MIRI-MRS: SHORT (A), MEDIUM (B), and LONG (C). Both short and long wavelength detectors for the MRS are used. TA is not chosen for either the target group MRS observation or the MRS background observation.
We want to use a dither pattern for the MRS observations. We click the Add button under the Dithers field, and a row with dither options appears. Above the Dithers field, in the drop-down parameters for Primary Channel, we select ALL, so that the dither pattern will be optimized for all channels. In the row that appeared in the Dithers field, under the Dither Type heading, we select 4-Point. Under the Optimized For heading, we select EXTENDED SOURCE because we are observing an extended source. Under the Direction heading, NEGATIVE is already selected because it is the only option. APT will refer to this dither configuration in the Exposure Parameters field as Dither 1.
Under the Mosaic Properties tab, we enter 2 for both Rows and Columns, in order to create the 2 × 2 mini mosaic. The defaut Row Overlap and Column Overlap of 10% are used. Under the Special Requirements tab, we click Add, then Position Angle, then PA Range. In the box that pops up, we set the range to 100 to 100 (Degrees), then click OK. We also click Add, then Timing, then Group/Sequence Observations Link, and in the box that pops up, we select observations 16 and 5, corresponding to the MRS target group observation and the MRS Background, respectively, and we click the checkboxes beside Sequence and Non-interruptible, then click OK.
After the Dithers Pane in the active GUI window, the Simultaneous Imaging drop-down parameters was set to YES. To the side of this, the Imager Subarray drop-down parameters was set to FULL.
Under this in the Exposure Parameters panel, we clicked Add 3 times, each corresponding to the 3 available MRS grating settings. One click of the Add button here brings up 3 rows: one for the MIRI imager, the next for the MRS long wavelength detector, and the other for the MRS short wavelength detector. Under the Wavelength Range column, for the first triplet of rows, the value was set to SHORT (A) for MRSLONG and MRSSHORT rows. For the second and third triplets of rows, the values were set to MEDIUM (B) and LONG(C), respectively. Under the Filter column, in the Imager rows, F1130W was selected. Under the Readout Pattern column, FAST was selected. Under the Groups/Int column, the values were set to 73 for the Long grating, 50 for the Medium grating, and 33 for the Short grating. Under the Integrations/Exp column, the value was set to 1 for all rows. Under the Exposures/Dith column, the value was set to 1 for all rows. Under the Dither column, the value was set to Dither 1 for all rows. The rest of the entries on each row are determined by APT from the previous entries.
The same is done for the MRS Background observation as for the MRS Target Group observation.
Complete APT observation template for the NIRSpec IFU
As discussed in the parent article and the Step-by-Step ETC Guide, observations will be taken using the G140H disperser and F100LP filter for the NIRSpec IFU for FMK1, FMK2, and FMK3. No TA is chosen, as the targets are all extended sources larger than the NIRSpec IFU aperture. The Dither Parameters drop-down options is set to CYCLING, and the dither SIZE is set to SMALL, with the Starting Point set to 1 and the Number of Points set to 4. This is the same as the 4-point dither pattern, according to the NIRSpec IFU Dither and Nod Patterns page. This is done for all 3 FMKs.
Also, for the 3 FMKs, under the Mosaic Properties tab, we enter 2 for both Rows and Columns, in order to create the 2 × 2 mini mosaic. The defaut row and column overlaps of 10% are used. For the NIRSpec IFU observation of FMK1 (Observation 6), under Special Requirements, we click Add, then Timing, then Group/Sequence Observations Link, and in the box that pops up, we select observations 6 and 17, corresponding to the NIRSpec IFU observation of FMK1 and its Background, respectively, and we click the checkboxes beside Sequence and Non-interruptible, then click OK. We do the same for the observation of FMK2 and FMK3 (Observation 7): for this one, under Special Requirements, we click Add, then Timing, then Group/Sequence Observations Link, and in the box that pops up, we select observations 7 and 18, corresponding to the NIRSpec IFU target group observation of FMK2 and FMK3 and its Background, respectively, and we click the checkboxes beside Sequence and Non-interruptible, then click OK.
In the Gratings/Filters panel in the active GUI window for each FMK's observation, we clicked Add. On the row that was added, we selected G140H/F100LP under the Grating/Filter column, and NRSIRS2 under the Readout column. Under the Groups/Int column, the entry for FMK1 was set to 11; for FMK2 and FMK3, it was set to 7. For all FMKs, the Integrations/Exp column was set to 1. The checkbox under Dither was checked, and AUTOCAL was set to NONE. For each knot's observation, another row was added for a leakcal observation. The entries for the leakcal row are the same as for the science target observation row, except that the checkbox under Dither is checked for the science observation (this is not user-editable) but not for the leakcal observation, while the checkbox for the leakcal observation is checked for the leakcal observation.
The same is done for the NIRSpec IFU Background, 11 groups observation (Observation 17) as was done for the FMK1 observation (Observation 6); likewise, the same is done for the NIRSpec IFU Background, 7 groups observation (Observation 18) as was done for the FMK2 and FMK3 observations (Observations 7 and 8, respectively).
Run Visit Planner
Main article: APT Visit Planner
To determine the visibility window of our proposed observation, we ran the Visit Planner Tool. First, we click an observation in the tree editor. Then we click on Visit Planner in the top tool bar, which changes the view in the active GUI window. Then we click the Run All Tools button at the right in the top tool bar. This shows us the observing window(s) for this target over the next ~19 months. APT assures us that all visits are schedulable.
Run Smart Accounting
Main article: APT Smart Accounting
To minimize excessive overheads, we ran Smart Accounting from the Visit Planner page by clicking the Run Smart Accounting button. Upon completion, exposure time and overheads is properly calculated and the Charged Time field in the active GUI window of the Proposal Information page is updated.
According to APT 27.3, the total charged time for this program after running Smart Accounting is 32.48 hours.
Hurford, A. P., & Fesen, R. A., 1996, ApJ, 469, 246
Reddening Measurements and Physical Conditions for Cassiopeia A from Optical and Near-Infrared Spectra