Optimization Strategies for the NIRSpec MSA Planning Tool

Optimization Strategies for the NIRSpec MSA Planning

ToolJames Muzerolle

Special thanks to NIRSpec teamlet members and APT developers:

Diane KaraklaTracy BeckJason TumlinsonJeff ValentiTom DonaldsonRob DouglasKarla Peterson

Quick NIRSpec overview

• 3 spectroscopic modes: MOS, fixed slit, IFU• 3 resolutions: R ~ 100 (prism), 1000 and 2700

(gratings)• effective wavelength range 0.6 – 5 microns• FOV ~ 3.6’ x 3.4’

Microshutter Array (MSA)

4 x 365 x 171 shutters, individually addressable

shutter pitch = 0.26” x

0.51”, (actual FOV = 0.2” x 0.45”)

activated with magnet sweep

prism spectral layout

R=2700 spectral layout

MSA planning tool prototype

(APT v17.0.3)

Preliminary optimization study

• IDL code to simulate planning tool analysis of target placement within MSA shutters

• heuristic iterative scheme to optimize the number of targets per MSA configuration from an input “candidate” target sample– grid of MSA center pointings and position angles– optimized solution = grid point with largest number of

targets– loop for multiple configurations

• test cases to evaluate various parameters:– input sample size/spatial distribution– number of “sky” shutters– including known failed shutters– dithers– target priorities

# cand Targ Set 1 Targ 1/2 Config 1/2 Fails? Test case

1009 102 407 5 n 1 center

1009 102 534 6 n 3x3 center grid, 3-shutter slitlets

1009 80 508 8 y

1009 118 505 5 y 2-shutter slitlets

1009 76 545 9 y shutter dither (0.26”)

1009 65 510 11 y gap dither (17.9”)

1000 64 519 11 y concentrated source distribution

25 9 16 2 y sparse sample, 3 orients

1009 (99, 100) 71 (24, 11) 528 (88, 76) 8 y target priorities

Optimization results

Default test case:• UDF-derived input candidate target catalog (1009 objects)• 3x3 center pointing grid, 20.1” x 36.2” offsets• 3-shutter slitlet• ideal MSA• 1 configuration per target set (no cross-slitlet dithers)


1009 102 407 5 n 1 center


1009 80 508 8 y


1009 76 545 9 y shutter dither (0.26”)

1009 65 510 11 y gap dither (17.9”)





Default test case with failed shutters


1009 102 407 5 n 1 center


1009 80 508 8 y1009 118 505 5 y 2-shutter slitlets

1009 76 545 9 y shutter dither (0.26”)

1009 65 510 11 y gap dither (17.9”)





Default test case with failed shutters,2-shutter slitlet


1009 102 407 5 n 1 center


1009 80 508 8 y


1009 76 545 9 y shutter dither (0.26”)

1009 65 510 11 y gap dither (17.9”)





Default test case with failed shutters,1-shutter dither (0.26”) in dispersion direction


1009 102 407 5 n 1 center


1009 80 508 8 y


1009 76 545 9 y shutter dither (0.26”)

1009 65 510 11 y gap dither (17.9”)





Default test case with failed shutters,detector gap dither (18”)

prism spectral layout

R=2700 spectral layout


1009 102 407 5 n 1 center


1009 80 508 8 y


1009 76 545 9 y shutter dither (0.26”)

1009 65 510 11 y gap dither (17.9”)





Recommendations

• Tool should incorporate iterative scheme for optimizing the number of targets in a configuration using a grid of center pointings and/or position angles.

• Account for “acceptance zone” where flux losses are minimized.• Failed shutters must be tracked and updated. No targets in failed

closed. Generate warnings for targets in rows with failed opens.• Include an option for dithers requiring separate configurations

(e.g., detector gap coverage), for an arbitrary number of dithers.• Target priorities, with an arbitrary number of layers, should be a

key part of the optimization scheme.• Include a diagnostic plot summarizing characteristics of all targets

in a given configuration, such as relative shutter position, priority, dither status, user-defined properties (magnitude, redshift, etc).

To do

• optical distortion across the FOV must be included, with the ability to update the distortion solution as needed

• better treatment of prism spectra (can fit more than one in the same shutter row without overlap)

• target acquisition: visualization and selection of reference stars, avoiding failed closed shutters

• explore more observing scenarios

Optimization Strategies for the NIRSpec MSA Planning Tool

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