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- Should I dither for grism time-series imaging observations?
No, it’s not allowed.
NIRISS
In addition to the required question in bold-faced, answer an additional 2 questions from this list.
1. What is the field of view and wavelength coverage of NIRISS? What is the pixel scale?
The FoV is 2.2’ x 2.2’. Wavelength coverage is between 0.60 and 5.0 microns. The pixel scale is 0.065” / pixel for all four observing modes: wide-field slitless spectroscopy, single-object slitless spectroscopy, aperture-masking interferometry, and imagine.
What is the difference between the NIRISS readout patterns? Which should I choose for my science?
The JWST NIRISS detector allows two readout patterns—NIS and NISRAPID—that determine the sampling cadence for non-destructive readouts. NISRAPID is mostly used for bright targets, while NIS allows longer integration for fainter targets.
An integration consistents of Ngroups which each consist of Nframes. NISrapid has 1 frame per group, NIS has 4 frames per group.
For which NIRISS observing modes do I have to use a target acquisition?
TAs are supported for two NIRISS observing modes: single object slitless spectroscopy (SOSS) and aperture masking interferometry (AMI). While a TA is only required for those observing modes when a subarray is used, it is also strongly recommended for the full frame detector readout to ensure that the target is always placed on the same detector pixel.
Which NIRISS observing modes require dithering?
Dithering with JWST NIRISS is required for the wide field slitless spectroscopy (WFSS) mode to improve point spread function sampling, as well as mitigate the effects of bad pixels and sensitivity variations across the detector.
What are the four factors to consider when choosing a PSF reference (i.e., calibrator) star for an AMI observation?
6. I want to observe a galaxy cluster field with NIRISS WFSS. Is there a good example of how to set up my observations? How do I remove contamination from overlapping spectra?
NIRSpec
In addition to the required question in bold-faced, answer an additional 2 questions from this list.
1. What is the wavelength coverage of NIRSpec? What is the pixel scale of NIRSpec?
The JWST Near Infrared Spectrograph (NIRSpec) enables 0.6–5.3 μm spectroscopy, always with 0.10”/pixel on all four modes: MSA spectroscopy, IFU spectroscopy, Fixed-slit spectroscopy, and bright object time series.
What is the field of view of the NIRSpec Micro-Shutter Assembly? What is the field of view of the NIRSpec IFU?
For the MSA, 3.6’ x 3.4’, for the IFU, 3” x 3”.
3. What is the estimated best possible accuracy for target acquisition for the micro-shutter assembly shutters and which TA method will deliver it?
4. I have ground-based and Spitzer imaging of my field. Do I need NIRCam pre-imaging to ensure that my objects are precisely located in their MSA shutters?
Yes, either HST or JWST for pre-imaging.
5. There are bright stars in the MSA FOV that will cause leakage and will contaminate my IFU observations. What are the mitigation strategies that can be implemented when designing the observations?
6. What do I do if I need precise centering for a target that’s too bright for WATA?
I want to use a 0.2" fixed slit to observe a source with an emission feature at 1.355 microns. Which slit should I use? Can I use both of the A slits for this?
Astronomer's Proposal Tool (APT)
In addition to the bold-faced required question, answer an additional 2 questions from this list.
1. When I enter an observation in APT, there is a box at far right labeled “ETC Wkbk.Calc
ID”, but there is no context-sensitive help available. What am I supposed to put in that box, and is it a required input?
The ETC workbook calculation ID, and shows that you checked the validity of things in the ETC.
The JWST Web site lists accepted Early Release Science programs:
http://www.stsci.edu/jwst/observing-programs/approved-ers-programs
I am interested in looking at program ID 1334, “The Resolved Stellar Populations Early Release Science Program” as an example, and I understand the APT files for the approved Early Release Science Programs can be loaded directly into APT for inspection. How do I do that?
File -> Retrieve from STScI -> Proposal ID
If I am requesting a sequence of observations that need to be chained together in time (hence I put a special requirement in to make a non-interruptible sequence), is there a maximum time limit for such a sequence?
4. Why does my observation have "Implicit" special requirements in APT, and why can't I edit them?
5. Which APT observation templates fall into the category of mini-mosaics?
6. I see an option for "Module" in the NIRCam APT template. What do these two options refer to?
Both modules or B modules. I think that one might just use “B” module, for example, if they want to save on bandwidth, or if they only need long-wavelength data.
Exposure Time Calculator (ETC)
In addition to the bold-faced required question, answer an additional 2 questions from the list.
1. The ETC will give me a warning if I start inputting parameters that are not supported by APT, right?
APT warnings and errors are not always reflected in ETC: The ETC needs to be able to support engineering users as well as astronomers. Hence, it was developed to allow a user to choose values for various parameters that are not available by default, but can be accessed for engineering purposes. APT contains numerous warnings and errors that alert users when they are attempting to select options that are not available by default. Unfortunately, those errors and warnings are not always reflected directly in the ETC. That is, the ETC may let you select options that will be considered invalid when the information is transferred to the appropriate APT template.
Can I upload a custom spectrum for my source for ETC calculations? What information should I provide, if so?
Column 1 should be the wavelength in µm and column 2 should be the flux density in mJy.
What options do I have for defining the flux distribution for an extended source?
. Choosing extended allows for flux distribution, normalization, and axial extent options. The flux normalization for extended sources may be done in integrated magnitudes or surface brightness units, and the selection made in the Shape tab will be reflected in the units used in the Renorm tab.
In the Hubble ETC, I can input my desired SNR and receive as output the necessary integration time. Why can't the JWST ETC optimize the number of groups and integrations for my signal-to-noise goal? Running a whole bunch of calculations is tedious... Is there a way to speed this up?
5. When should I use the IFU Nod off Scene strategy?
6. I would like to do additional analysis beyond what the ETC reports. Is there a way to access the output data products so I can use my own software tools for further analysis?
JWST Help Desk Homework Questions
Please answer all questions below.
- Announcements such as new APT and ETC releases/downtimes, Call for Proposals downtimes, Call for Proposals, etc. are posted on the Help Desk homepage (jwsthelp.stsci.edu, see screenshot below). What is the latest announcement posted on the homepage?
JWST Video Tutorials now available! !!!
- From the Help Desk homepage (jwsthelp.stsci.edu) you can search for answers to your questions. Search results will give Knowledge Base articles first and then JDox results. You can use the sidebar tree to filter for specific types of articles. See the screenshot below for the search results for “APT MIRI”. Use the Help Desk search bar to find out why you may be having trouble connecting to the APT server. Explore using the sidebar tree to filter types of articles.
Done.
- If you can’t find an answer to your question using the search function, you may submit
a question (otherwise known as a “ticket”) for a member of the Help Desk staff to
answer. You submit a question by clicking on the “Get Help” icon on the
homepage. This will send you to a page of “catalogs” to choose from to get an answer
quicker (See example screenshot below). If you can’t determine what catalog to
choose you may also choose “General”. What catalog would you submit to if you have
a question about adding an investigator to your proposal?
(You may have noticed while answering Question 2 that your search results may also
send you directly to the page to submit your question, that is also fine.)
APT support.
- Practice using the Help Desk by submitting a practice ticket to the catalog “JWST
Master Class”. Request that your ticket be proprietary, use the subject “My Test
Ticket”, and the description “Hello, I am practicing using the Help Desk for the JWST
Masterclass, please send me a response. Thank you.”
Done.
- After submitting your question you will see your ticket under “My Open Tickets” in the
top menu bar. You can view and update your tickets here. You may add an
attachment or a collaborator to the “watchlist” (the collaborator will then receive all
future updates to the ticket in an email. Note: you can add also someone to watchlist
when you first submit your ticket). Re-open the practice ticket you submitted in
Question 4 and either add someone to the watchlist or send an attachment image of
your favorite astronomical target. See example screenshot below:
Done.
