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JWST Training Workshop @ UC Irvine

Date: Tuesday, February 4th, 2020

Time: 9am - 5pm 

Venue: UCI Beall Applied Innovations - Venture Cove B

Location: 5141 California Avenue, Irvine, CA 92697 (Free parking in the lot)

Capacity: 40 

Contact: Hooshang Nayyeri (hnayyeri@uci.edu) and Vivian U (vivianu@uci.edu)


HW2 - 

Understanding JWST detectors questionnaire


1. What is the difference between the JWST NIR and MIR detectors?

2. What is the fundamental difference between a CCD and a JWST detector readout?

3. What is a frame?

4. What is a group?

5. What’s the meaning of “group gap” or “dropframes” in the JWST NIR detectors?

6. What is a reset?

7. What is an integration?

8. What is an exposure?

9. Suppose you have data from a CCD and from a JWST detector. They both reach the saturation level in one-half of the total integration time. Can you describe what the main difference is? Can you recover information in the saturated pixels?

10. What will be the impact of a cosmic ray in a JWST integration? Can information be recovered?

11. a) What is the practical difference between a MIRI SLOW mode exposure and a NIR exposure with NFRAMES=8? b) Which has a higher data rate: a single MIRI Si:As

detector running in SLOW mode or a single NIRCAM H2RG detector using the MEDIUM8 readout pattern?

https://jwst-docs.stsci.edu/mid-infrared-instrument/miri-instrumentation/miridetector-overview/miri-detector-readout-overview/miri-detector-readout-slow

https://jwst-docs.stsci.edu/observatory-functionality/jwst-data-rate-and-datavolume-limits

12. Given a certain readout pattern, why is the group time different for full and subarray mode?

https://jwst-docs.stsci.edu/near-infrared-camera/nircam-instrumentation/nircamdetectors/nircam-detector-subarrays

13. If a user defines a single NIRCam exposure (i.e. no dithers) with all modules in FULL array and BRIGHT1 readout pattern, that uses 10 groups and 1 integration, the exposure time is 203.99 second. 10 groups and 2 integrations result in 418.73 seconds. Why the total time of 2 integrations is not twice as long as one? Can you guess why that would not be the case for MIRI?

https://jwst-docs.stsci.edu/jppom/visit-overheads-timing-model/instrument-specificoverheads/nircam-overheads


HW1 -

Cross Instrument

In addition to the required questions in bold-faced, answer an additional 1 question from this

list.

1. What's the first thing I should do when preparing my proposal?

2. What observing methods does JWST support?

  • E.g. MIRI MRS, NIRCam Imaging, NIRISS AMI, NIRISS SOSS, NIRISS WFSS, NIRSpec IFU + FS, and parallels

3. How do I know when a given target is visible to JWST?

  • use visibility checker 

4. When should I propose for NIRISS Wide Field Slitless Spectroscopy (WFSS) instead of

NIRCam WFSS?

5. If I want to observe the spectra of transiting exoplanets, what spectroscopic JWST

observing modes are available to me?

6. Which JWST instruments offer standard imaging? What is the wavelength coverage of

the imaging modes?

7. I would like to obtain spatially resolved 2-D spectroscopy with JWST. Is that possible? If

so, what observing modes support this, and what wavelengths are covered?

  • MIRI MRS (4.9-28.8 um), NIRSpec IFU (0.9-5.2 um)

8. What JWST observing modes will allow me to observe faint companions near bright host

objects?

MIRI

In addition to the required questions in bold-faced, answer an additional 2 questions from this

list.

1. What is the wavelength coverage of MIRI? What are the pixel scales for the various

observing modes?

  • 4.9-28.8 um; pixel scale = 0.11"/px for imaging and low-res spectroscopy, 0.196-0.273 for MRS

2. For what MIRI observing modes should I dither? Is there a limit for the amount of time I

should spend in a given dither position?

3. What is the field-of-view & wavelength range for the MIRI IFU (medium-resolution

spectroscopy) channels?

4. What separations between a faint companion and bright host can I achieve with the

MIRI coronagraphic masks? What are the central wavelength coverages of these masks?

5. When observing with the low-resolution spectrometer (LRS), should I choose slit or

slitless spectroscopy?

6. When using MIRI MRS Simultaneous Imaging, will I get imaging observations of my

target "for free"? What is this mode used for? When should I choose to not use this

option?

  • Yes, it's the default mode and highly recommended for astrometry purposes. Don't use this option if a bright target were to be expected in the imager's FOV that would saturate during a long MRS observation.

7. When should I take a dedicated background observation?

  • if an extended object filled the entire MRS FOV or if an extended source dither pattern was specified and the total offset was insufficient for pairwise background subtraction

NIRCam

In addition to the required question in bold-faced, answer an additional 2 questions from this

list.

1. What is the wavelength coverage, field of view, and pixel scale for NIRCam's shortwavelength

and long-wavelength detectors?

  • Short (0.6-2.3 um; two 132"x132" FOV, 0.031" / px) and long (2.4-5.0 um; two 129" x 129" FOV, 0.063 / px)

2. I would like to observe the gaps in between NIRCam's A & B module when using

imaging. What dither pattern should I use? What dither pattern should I use for NIRCam

Wide Field Slitless Spectroscopy?

3. What NIRCam observing modes support mosaicking? When I should a mosaic and when

should I dither?

  • NIRCAm imaging and wide field slitless spectroscopy; Primary dithers are telescope pointing maneuvers (4"–100") to fill gaps in sky coverage between detectors and mitigate flat field uncertainties. Mosaics are, typically, large pointing shifts (arcminutes) to tile over areas larger than the NIRCam field of view (5.1' × 2.2').

4. Which NIRCam readout patterns have skipped frames?

  • bright1, shallow2, shallow4, medium2, medium8, deep2, and deep8

5. What coronagraphic masks are offered by NIRCam, and what wavelength ranges do they

cover?

6. Should I dither for grism time-series imaging observations?

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?

  • 2.2' x 2.2', 0.6-5 um, 0.065" / px

2. What is the difference between the NIRISS readout patterns? Which should I choose for

my science?

3. For which NIRISS observing modes do I have to use a target acquisition?

  • single object slitless spectroscopy (SOSS) and aperture masking interferometry (AMI)

4. Which NIRISS observing modes require dithering?

  • wide field slitless spectroscopy (WFSS), to improve PSF sampling

5. 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?

  • 0.6-5.3um, 0.1"/px

2. What is the field of view of the NIRSpec Micro-Shutter Assembly? What is the field of

view of the NIRSpec IFU?

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?

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?

  • if determined necessary, subtract MSA leakage using dedicated MSA leakage exposures

6. What do I do if I need precise centering for a target that’s too bright for WATA?

  • (1) use the standard MSATA algorithm which utilizes faint reference stars in the field, (2) acquire a nearby fainter star and offset to the desired bright target (fixed targets only), or (3) observe without using any target acquisition.

7. 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?

  • optional, but strongly encouraged for any target acquisition specifictions; enter the Calculation ID from ETC workbook

2. 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?

3. 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?

  • Implicit requirements are placed on observations automatically by the scheduling system, and are not editable; they are shown to the user for information only. 

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?

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?

  • yes?

2. Can I upload a custom spectrum for my source for ETC calculations? What information

should I provide, if so?

3. What options do I have for defining the flux distribution for an extended source?

4. 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?

  • Unlike other exposure time calculators, the JWST Exposure Time Calculator (ETC) does not provide an option for reverse calculation of exposure duration parameters starting from a given signal-to-noise ratio (S/N) because there is often no unique solution for a given subarray/readout combination in terms of groups, integrations, and exposures. Instead, a batch expansion capability is available to test a number of different detector parameters (groups or integrations) to determine which set of parameters results in the desired S/N. 

5. When should I use the IFU Nod off Scene strategy?

  • For IFU Nod Off Scene, there is no source flux in the off-source nod position because it is completely off the scene and only contains the sky background. Only half of the exposure time required for the IFU Nod Off Scene strategy is on-source and hence the SNR is lower.

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.

1. Announcements such as new APT and ETC releases/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?

  • ETC1.5 is released

2. 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.

3. 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?

  • APT support?

(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.)

4. 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

5. 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
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