Page History
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Venue: UCI Beall Applied Innovations - Venture Cove B
Location: 5141 5270 California Avenue Suite 100, Irvine, CA 92697 (Free parking in the lot)
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Contact: Hooshang Nayyeri (hnayyeri@uci.edu) and Vivian U (vivianu@uci.edu)
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HW2 HW3 -
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ETC
Exercise 1
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2. What is the fundamental difference between a CCD and a JWST detector readout?
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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o What do you think the “out-of-date” field in the workbook list means?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?
6. What is a reset?
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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)
87. What is an integration?8. What is an exposure?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
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