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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)
...
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o What do you think the “out-of-date” field in the workbook list means?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
list.
1. What's the first thing I should do when preparing my proposal?
- read through the Call for Proposals and get familiar with JWST Science policies
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
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?
- read through the Call for Proposals and get familiar with JWST Science policies
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
...
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.
...
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
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?2. The JWST Web site lists accepted Early Release Science 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?
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?
...
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
...
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
...
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 about adding an investigator to your proposal?
- APT support?
(You may have noticed while answering Question 2 that your search results may also
...
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
...
your favorite astronomical target. See example screenshot below:
- done
