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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: 5270 California Avenue Suite 100, Irvine, CA 92697 (Free parking in the lot)
Capacity: 40
Contact: Hooshang Nayyeri (hnayyeri@uci.edu) and Vivian U (vivianu@uci.edu)
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HW3 -
ETC
Exercise 1 exploration:
o What do you think the “out-of-date” field in the workbook list means?
- version control
o Try to find out how you can share a workbook with a collaborator. Experiment with read and write permissions.
- Add user by email, permission checkboxes
Exercise 2 exploration:
o Find the known issues under the help menu. Which one, if any, do you think could most affect your favorite science case?
- For IFU calculations, which allow the user to choose between two strategies, changing the strategy for a selected calculation will revert to the default settings to the newly selected strategy. All previous user inputs in the strategy tab will be lost. (#1072)
- The extinction calculation assumes a simple relationship between the magnitude and the column density. It is correct for a source with a smoothly varying or reasonably flat input flux density. It will be inaccurate for sources with extremely steep gradients.(#1884)
- NIRSpec noise is underestimated in some readout patterns.(#2429)
- The ETC allows detector parameters that may lead to large exposure times. Users are advised to check with APT and choose detector parameters accordingly. (#2099)
- For near-infrared detectors, APT allows 1 group per integration, but the ETC does not because the magnitude of systematic errors will not be known until measurements are made in orbit. (#246)
Exercise 3 exploration:
o Note the two different slopes in the signal-to-noise ratio (SNR) for increasing the number of groups and increasing the number of integrations. What do you think
causes this behavior?
- integration takes longer because it includes readout time in between
o Experiment with other readout patterns (under the Detector Setup tab) to find the highest SNR for a total exposure time of about 1000 seconds. What is it?
- medium8
Exercise 4 exploration
o A scene can contain multiple sources. Using the “Offset” parameter in the scene, determine the minimum unblended separation of a binary star for your chosen
NIRCam imaging filter.
- ??
Exercise 5 exploration
o What is the faintest point source that will yield a “SOSS or AMI faint” target acquisition without a warning for NIRISS?
- 14 mJy at 1.3 microns
Exercise 6 exploration
o What if you knew that the surface brightness of Pluto at 3 micron is 1000 MJy/sterad. How would you renormalize the spectrum to this value?
- "Source Editor" → "Renorm", and "Shape" → "Surface Brightness"
Exercise 7 exploration
o How can the “Groups Before Saturation” image help you quickly determine the optimal number of groups?
- It displays the min. number of groups before saturation - usually at source center where the surface brightness peaks.
o How much exposure time is needed to observe Pluto with the NIRSpec IFU in high resolution at 2.7-5.2 micron with a minimum SNR of 20?
- about 300 seconds
Exercise 8 and 9 exploration
o Create a new workbook and share it with a colleague. Now delete your version of the workbook. What happens with your colleagues’ version?
- done
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HW2 -
Understanding JWST detectors questionnaire
1. What is the difference between the JWST NIR and MIR detectors?
- Different types of electronics driven by wavelength range over which photons can be efficiently detected: H2RG detectors for NIR and Si:As detectors for MIRI
2. What is the fundamental difference between a CCD and a JWST detector readout?
- JW detector uses the MULTIACCUM readout method that reads and records individual pixel signal multiple times during an exposure, recording how wthe pixel charge/signal increases with time (as opposed to CCD that only reads out at the end of an exposure).
3. What is a frame?
A single read of all pixels in the detector array or subarray
4. What is a group?
on-board average of one or multiple frames
5. What’s the meaning of “group gap” or “dropframes” in the JWST NIR detectors?
these are frames between groups that are sampled but not included in the group average
6. What is a reset?
stops the pixels from accumulating charge and resets them to the bias level
7. What is an integration?
a set of groups starting with the first group after a reset and ending with either the last group before a reset (NIR) or the last read-reset group (MIRI)
8. What is an exposure?
a set of identical integrations that are separated by only a constant number of resets (nominally 1)
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?
- You can recover info in saturated pixel in JW detector but not from CCD because the charge/signal as a function of time is recorded in JW detector.
10. What will be the impact of a cosmic ray in a JWST integration? Can information be recovered?
- impact is a jump in signal as function of time; yes info can 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
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HW1 -
Cross Instrument
In addition to the required questions in bold-faced, answer an additional 1 question from this
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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.
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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
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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
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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
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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
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your favorite astronomical target. See example screenshot below:
- done
