1. Diane Karakla JWST Community Lecture Series Feb 28, 2017
Planning MOS Spectroscopy with the NIRSpec Micro-Shutter Array (MSA) The MSA Planning Tool (MPT) was developed with the help of G. Curtis, T. Beck, K. Gilbert, J. Valenti, S. Kassin, and several others based on an original prototype by K. Pontoppidan.
Diane Karakla
JWST Community Lecture Series
Feb 28, 2017

2. Outline Timeline for MOS observing
Download latest version of APT (currently APT ) from:
Timeline for MOS observing
Target Acquisition & Pre-imaging considerations
MOS observation planning challenges
Key planning parameters and strategies
Planning tool outputs and assessment tools
DEMO of the MSA Planning Tool in APT

3. Timeline for MSA Observations
MOS Spectroscopy will require a 2-phase approach:
Idea for
MOS
Survey
MSA
Observations!
NIRCam
Pre-Imaging
Proposal
Submission
TAC
acceptance
Fixed Orient
assigned
Program
Long Range
Plan
Scheduling
Proposal Submission: Users must request the time needed (including overheads) to observe an expected number of targets to desired exposure depths.
The MSA Planning tool (MPT) can be used with simulated or existing catalogs to explore the effects of planning choices (dithers, slit length, etc.) on
the number of observable targets, and
the number of MSA configurations needed to obtain all dithered exposures.
How many visits will be needed to obtain those targets.
 Use the tool to best estimate the time required.

4. Timeline for MSA Observations
MOS Spectroscopy will require a 2-phase approach:
Idea for
MOS
Survey
MSA
Observations!
Proposal
Submission
TAC
acceptance
Program
Long Range
Plan
Scheduling
NIRCam
Pre-Imaging
Fixed Orient
assigned
To allow some scheduling flexibility, most MOS observations will be assigned an orient after TAC acceptance.
Program Submission: After an Orient is assigned, and pre-imaging becomes available.
Pre-Imaging may be needed to
identify potential targets
identify suitable MSA reference stars for target acquisition
obtain accurate positions
make MSA configurations

5. Observing Considerations
Does your science require precise positioning delivered by MSA TA with reference stars?
Do you need NIRCam pre-imaging?
Pre-imaging with NIRCAM will deliver this accuracy.
TA type
Delivered Pointing accuracy
Catalog relative astrometric accuracy
Science Goal
Optimal
<20 mas
(0.1 shutter width)
<25 mas
~ 5 mas
~ 15 mas
Best possible photometric accuracy
Relaxed
<~ 50 mas
< 40 mas
Extended sources, or reduced flux accuracy w/ MSA
Verify Only
Point and Shoot
~100 mas TBD
NO reference stars required.
Limited science cases
MSA TA
Also possible with careful
HST imaging
Imaging should ideally cover ~5 x 5 arcmin2 for
planning flexibility.
MSA TA requires 5-20 reference stars (An alternate TA methodology is planned for moving targets).
NIRCam pre-imaging possible in same cycle – can define NIRCam pre-image in same program. NIRSpec observation must follow by > 6 weeks.

6. Planning in MPT: Target Acquisition
MPT will also assist with MSA Target Acquisition using Reference Stars:
Done at detailed program submission once an orient is assigned: Reference star selection for MSA TA happens at the Visit level.
NIRSpec Target Acquisition Error vs. Catalog Astrometry
TA accuracy depends on the input catalog relative astrometric accuracy and the number of reference stars (5 to 20).
For planning reference stars, at detailed program submission the Catalog must contain columns with count rates in the NIRSpec TA filters. (STScI will provide a script.)
Figure from T. Beck
Proc. SPIE 9910 July

7. Observation Planning Challenges
Gap (~20”)
The MSA is a fixed grid (with shutter bars that vignette light from sources)
Gap between the 2 detectors  missing wavelengths.
Source positions in MSA require knowledge of optical distortions/ velocity aberrations at a planned Aperture Position Angle.
Quad 4
Quad 2
Quad 3
Quad 1
Failed Closed Shutters
The MSA has Failed shutters, shorted rows/columns. Shutter status can evolve!
Solution  use MPT!
Download APT (including MPT) here
Dither to cover gap, mitigate detector artifacts, improve resolution, observe sources behind bars or mounting plate.
observe as many sources as possible at all dithers!
MPT will deliver optimal pointings and MSA configurations!

8. Key Planning Parameters in MPT: Target Weights
A source catalog is first input to the MPT.
Target weights can be added in catalog. Relative weights can be based on anything.
Integer values. W(100) = 100 x W(1).
Order your input catalog by target weight before ingest.
Create a Primary candidate set, and an optional Filler candidate set to work with in MPT.
Only the weights of the primaries are used during planning.
Observed targets shown in red
The best pointing is determined from the (weighted) Primaries.
Fillers help to optimize the MSA configuration.
If you want “extra” observations of your Primaries, include them in your Fillers list.
Primary Candidate List
100 1 …
Source Weight ID

9. Key Planning Parameters in MPT: Target Weights
Can optionally use Target Weights (provided in input Catalog)
Observed targets shown in red
Targets of large weight are much more likely to be observed
Helps to order catalog by weight.

10. Key Planning Parameters in MPT: Slitlet Shape & Shutter Margin
Slitlet shape (can be 1, 2, 3, or 5 shutters)
Shutter margin to limit slit losses (5 choices): *
Perfectly centered
NIRSpec MSA Slit Throughput vs. Wavelength
Unconstrained
Open Shutter Area
A catalog relative accuracy of ~15 mas is needed to effectively constrain source centering.
Midpoint
Constrained
Tightly Constrained
Figure from T. Beck
Proc. SPIE 9910 July
Shutter Planning Constraints

11. Key Planning Parameters in MPT: Monte Carlo optimization of the MSA configuration
User can choose whether to re-order the Primary candidate list at each pointing. It can increase the number of targets observed at that pointing. Example:
MSA Config 1
MSA Config 2 5 1 2 4 3
After 1 MC shuffle 5 1 2 4 3
Source Order 1: 1 2 3 4 5
2 successful sources
Source Order 2: 3 4 5 1 2
3 successful sources!
Can also customize MSA configurations in the manual planner. Tedious!

12. Key Planning Parameters in MPT: Search area & Dithers
Users define a search grid on the sky. Each grid point is a test pointing.
Users can confine the search area on the sky.
Users can apply Fixed dithers or Flexible dither constraints – e.g. gap coverage
Fixed dithers: Translate MSA config pattern to new dither point.
Flexible Dithers: User specifies a min or max separation between dither points in spectral and/or spatial direction.
This method handles relative distortions between dithers, so larger dithers are fine.
At each grid point, an MSA configuration is built, and sources are tallied. Can be optimized with MC shuffling.
Multiple pointings are tested at each dither step, building families of possible solutions.
The best family is chosen. (One that observes the largest number of highly-weighted sources over all dithers.)
(Individual sources are not matched from one dither point to the next! It’s done at the end.)
MSA
Config 1
Config 3
Config 2
(0,0)
(0,-4)
dispersion
spatial
(6,-4) * * *
SMALL dithers only! <~ 10 arcsec

13. MSA Planning Tool outputs
A Plan with:
A list of preferred pointings,
and the MSA configurations required for each pointing
associated sources that will be observed
After assessing plans, select a plan and create an Observation. APT will break an observation into Visits based on pointings (and duration).
NOTE: There are practical limits on the combination of key parameters:
- Number of sources in the primary list
- Number of pointings to test (search grid step size and area)
- Number of dither points
INPUTS

14. Review Plan Results Ability to select one or more exposures and
filter plan results to list primaries (or fillers or contaminants), or all observed sources. 1 2
View successful targets in all selected exposures
Histogram of targets from the selected and filtered results.

15. APT/MPT Visualization
MSA slitlets from a single pointing can be displayed on an image of the field in Aladin.
Source positions from one of the following lists
can be plotted in Aladin:
the catalog,
a candidate list made from the catalog, or
the target list (observed MSA sources)

16. Plan Assessment Tools
There are some nice built-in tools to help assess plans:
Different Exposure views
Green=Primaries
Blue=Fillers
Black=contaminants
MSA Shutter View
Collapsed Shutter View
Right: MSA shutter view. Targets are shown on a sketch of the MSA for one exposure. Users can click on or highlight targets for cross-examination with other views.
Left: Collapsed shutter view showing target centering results
0.”46
0.”2
0.”06

17. MPT “Planner” Inputs (Demo values in green)
Input a catalog of sources (required: ID, RA, Dec … at proposal submission. For detailed program submission: “Stellarity”, “Reference” [Y/N], plus 3 NIRSpec filter band magnitudes are also required.) Download Rafelski HUDF catalog from JWST Comm. Lecture website. The catalog was weighted by redshift2 and ordered by weight. I increased the weights for a few hundred of the most distant sources.
Next, filter the catalog within MPT to define a set of Primary candidates (Z_BPZ > 5, Mag_F160W < 98.9) and (optional) Filler candidates (Z_BPZ > 3, Mag_F160W < 98.9)
Select a feasible Aperture Position Angle (MSA orientation wrt N ecliptic pole). New TVT tool distributed as part of STScI’s AstroConda python distribution package. See JWST Community Lecture by Bill Blair from Jan 31, Aperture PA = 45.0 (degrees)
Select a slit length (1, 2, 3, or 5 shutters) Select the 3-shutter slitlet.
Select slit margin to limit slit losses (“Midpoint”)
A list of exposure specifications (gratings/filters, duration parameters). Use the ETC to determine exposure parameters needed to achieve desired S/N. (~1000 sec exposures: Use NRS readout, Ngroups=23 Nints=1)
INPUTS

18. MPT “Planner” Inputs (continued)
Specify dithers: nod in slitlet (check the box), primary dither constraints (add 1 Flexible dither constraint with dispersion separation >= 18 arcsec).
Search grid parameters (location, width and step size): use default grid area, step size = 5 arcsec.
Options to use source weights, or enable MC shuffling. Use weights (check the box), do not “Enable Monte Carlo” shuffling (leave the box unchecked).
Number of MSA configurations desired (it will display the number of configurations needed per target set). Select 2 to make a single target set with a 2-point dither.
Generate a Plan! (click “Generate Plan” at the bottom of “Planner” pane)
SAVE your APT program after each Plan is generated
Create an Observation (click “Create Observation” at the top of “Plans” pane)
Save again!
INPUTS

19. Start Demo
Extra slides follow

20. The MSA Planning Tool (MPT)
MPT is in APT, available at apst.stsci.edu
The tool is available from the Observation Folder level in the “tree editor”
APT is released every ~6 months

21. Planning in MPT: Target Acquisition
MPT will also assist with MSA Target Acquisition using Reference Stars:
At detailed program submission: Reference star selection for MSA TA happens at the Visit level.
The input Catalog must contain columns with fluxes in the NIRSpec TA filters. (STScI will provide a script.)

22. Review Plan Results Ability to select one or more exposures and
filter plan results to display only:
Primaries
Fillers
Contaminants
All targets
View target success through all selected exposures
Histogram of targets from the selected and filtered results.