Oct 17, 2001SALT PFIS Preliminary Design Review1 Operation Concepts Definition Document (OCDD) Chip Kobulnicky University of Wisconsin

Oct 17, 2001 SALT PFIS Preliminary Design Review 1

Operation Concepts Definition Document (OCDD)

Chip KobulnickyUniversity of Wisconsin


Operational Mode Description

• Operational modes are fully characterized by the configuration of 4 primary subsystems (“basis vectors” in 4-D) which describe the dataset being acquired.– Focal Plane Elements (spatial)– Dispersive Elements (spectral)– Polarizing Elements (polarization)– Detector (time)


Focal Plane Mechanism O – Open (implies direct acquisition & peak-up) S – Slit (Reflective Longslit Plate; implies visual acquisition & peak-up) M – Multi-slit mask (non-reflective carbon fiber; implies blind peak-up)Dispersive Elements I – Imaging (none) (Implies no camera articulation) F – Fabry-Perot Etalon (Implies no camera articulation) G – Grating (Articulated camera)Polarization Elements U – Unpolarized measurement (quartz block in place of waveplates) L – Linear polarization measurement (1/2 waveplate; max 4’ spatial field) C – Circular polarization measurement (1/2 and ¼ waveplate; max 4’ spatial field) A – All-stokes mode (both waveplates operational in sync; 4’ spatial field)CCD subsystem (see detector ICD for full explanation of readout modes) N - Normal readouts with exposure times of at least 3.6 s. Standard 2x2 binning H - High time resolution with frame-transfer in operation; max 4’ spatial field with lower half masked; objects confined to small region of chip just above CTB; continuous readout. V - Vertical shift operations, including vertical charge shuffling in conjunction with telescope nods to perform high-quality sky subtraction (spectroscopy) or off-band subtraction (Fabry-Perot spectroscopy), or time-series spectroscopy or spectropolarimetry. D - Drift scan or arbitrary charge-shuffling in use; CCD is clocked at a sidereal rate


Focal Plane

Disperser Polarization CCD readout

Common Name Commission?

O I U N Imaging Y

M I U H High Time Resolution Imaging U

M I L N Imaging Linear Polarimetry U

M I L H High Time Resolution Imaging Linear Polarimetry U

M I C N Imaging Circular Polarimetry U

O F U N Fabry-Perot Spectroscopic Imaging Y

M F L N Fabry-Perot Spectroscopic Imaging Linear Polarimetry U

M F C N Fabry Perot Spectroscopic Imaging Circular Polarimetry U

S G U N Longslit Spectroscopy Y

S G U H High Time Resolution Longslit Spectroscopy Y

S G L N Longslit Linear Spectropolarimetry U

S G L H Longslit High Time Resolution Linear Spectropolarimetry U

S G C N Longslit Circular Spectropolarimetry U

S G C H Longslit High Time Resolution Circular Spectral-Polarimetry U

M G U N Multi-slit spectroscopy Y

M G U H Multi-slit High Time Resolution Spectroscopy U

M G L N Multi-slit Linear Spectropolarimetry Y

M G C N Multi-slit Circular Spectropolarimetry U

O I U D Drift Scan Imaging & spectroscopy U

Available Operational Modes


Focal Plane Mechanisms

O – Open (direct imaging applications, Fabry-Perot spectroscopy)

2048 2048 2048

Impalas Detector Layout with 8’ diameter FOV40

96

4’


Reflective Slit Plate #Length Width (“)

1 7.5’ 0.45”

2 7.5’ 0.6”

3 7.5’ 0.9”

4 7.5’ 1.1”

5 7.5’ 1.3”

6 7.5’ 3.0”

7 Central 4’ 1.1” (variable) for spectral polarimetry

8 12” above CTB 1.1” (variable) for high speed spectroscopy

9 4’’ 1.1” w/ coronographic center

Table 1. Complement of Standard Reflective Focal Plane Plates

S – Slits (reflective tiled longslit plates)~9 held in focal plane magazine


Table 2: Standard Slitmasks

#Configuration Use

1 Masks lower 4’ x 8’ High Time res. Imaging

2 Masks upper and lower 2’ x 8’ (central 4’x8’ visible) Imaging and Fabry-Perot Polarimetry

Up to 30 other user-designed masks

M – carbon-fibre focal plane masks Laser-cut slits slit width: 0.11 – 0.35 mm

Standard Slitmask #2: Slitmask covers upper and lower ¼ of FOV

Standard Slitmask #1: Slitmask covers lower half of FOV


Dispersive Elements

I – Imaging (none) (Implies no camera articulation)

F – Fabry-Perot Etalon (Implies no camera articulation)

G – Grating (Articulated camera)1 of 6 gratings



Polarizing Elements

U – Unpolarized measurements (quartz block in beam)

L – Linear polarization (half-waveplate; rotates through 8 positions)

C – Circular polarization (half- and quarter-waveplate)

A – All-stokes mode (synchronized half- and quarter-waveplate)


CCD subsystem readout modes N - Normal readouts

Readout time 3.6 s standard 2x2 binning, 5e- read noise 11.2 s standard 2x2 binning, 3e- read noise 22.1 s 1x2 binning, 3e- read noise


CCD subsystem readout modes H - High time resolution with frame-transfer in operation; max 4’ spatial field with lower half masked, and possibly upper portions masked as well.

Bin RdN Read-------------------------1x2 3e- 11.0 s2x2 3e- 5.5 s1x2 5e- 3.2 s2x2 5e- 1.6 s


CCD subsystem readout modes H – all but a subsection of chip masked

Bin RdN Read-------------------------1x2 3e- 11.0 s2x2 3e- 5.5 s1x2 5e- 3.2 s2x2 5e- 1.6 s

2x2 5e- 2.0’ field 0.80 s 0.5’ field 0.20 s 0.12’ field 0.05 s (64 pix)(but image smear during 0.05 msec per row transfer)


CCD subsystem readout modes V - Vertical shift operations, including vertical charge shuffling in conjunction with telescope nods to perform high-quality sky subtraction (spectroscopy) or off-band subtraction (Fabry-Perot spectroscopy), or time-series spectroscopy or spectropolarimetry.

D - Drift scan or arbitrary charge-shuffling in use; CCD is clocked at a sidereal or other rate


Example of longslit spectroscopic mode operation

Typical sequence of operation:

Setup Telescope & Instrument (LOW OVERHEAD DESIGN GOAL FOR QUEUE MODE) Rotate telescope in Azimuth to correct location (few min; rate-limiting action) Select & insert filter (43 s) Select & insert grating (25 s) Select & insert longslit plate to be used (50 s) Articulate camera to desired position angle (<70 s) Acquire Field/Target Image field w/SALTICAM off reflective slitplate (2’ FOV) Locate desired object and move tracker to place object on slit Do Science

Begin tracking/guiding using either guide probes or slit viewer camera Begin exposure Insert cal. lamp & take arc exposure

Data Rate: 6154 pixels spectral x 4096 pixels spatial at >3.6 s total readout time

Target acquisition: By guide probe, and using visual peak-up with SALTICAM as slit viewing camera.

Tracking During Exposures: By guide probe, or by reflected light from slit viewed by SALTICAM.

Sim

ulta

neou

s!


Example of multi-slit (slitmask) spectroscopic mode Setup Telescope & Instrument Rotate telescope in Azimuth to correct location (few min; rate-limiting step) Select & insert filter (43 s) Select & insert grating (25) Select & insert slitmask to be used (50 s) Articulate camera to desired position angle (<70 s) Acquire Field/target (no view of slit, like nearly all multi-slit spectrographs) Insert SALTICAM fold mirror Image field with acquisition camera (SALTICAM) to locate alignment stars Perform offset to place alignment stars at proper location on focal plane

(blind, but calibrated offsets) Remove fold mirror Perfect alignment by taking a series of exposures while performing a patterned dither

on skyLocation of maximum signal is used as final alignment position (0.5s x 9)

[ fallback acquisition plan is direct imaging through unarticulated camera] Do Science Begin tracking/guiding using guide probes Begin science exposure Insert diffuser/cal lamp and do arc exposures

Data Rate: 6154 pixels spectral x 4096 pixels spatial at >3.6 s total readout timeTarget acquisition: By SALTICAM, guide probe, and dithered exposure peak-upTracking During Exposures: By guide probe

Sim

ulta

neou

s

Pea

k-up

per

form

edIn

spe

ctra

l mod

e


Instrument Commissioning Plan

• Let science drive commissioning Goal:6 science programs corresponding to each major instrument mode• Start with simplest modes (i.e., imaging)• Fully commission all “basic” modes• Leave specialized modes to users for shared-risk

basis• Reduction Software: standard community tools


Overview of Modes Commissioned by Instrument TeamEst Time. Mode Science Program----------------------------------------------------------------------------------------3 d Imaging TBD Nordsieck5 d Longslit Spectroscopy TBD Kobulnicky4 d High Time Res. Spectroscopy Magnetic CVs Buckley4 d Fabry-Perot Spectroscopy TBD Williams 4 d Multi-slit Spectroscopy PNe in Nearby Galaxies Kobulnicky5 d Polarimetric Imaging/Spectra Be Stars in the LMC Nordsieck25 d (on telescope; based commissioning for other major instruments)


Other possible user-commissioned modes (extensions of team-commissioned modes)

High Time Resolution Spectral-Polarimetry Fabry-Perot Spectral-PolarimetryCircular polarimetryCircular Spectral-PolarimetryAll-stokes PolarimetryHigh Time Resolution Multi-slit Spectral PolarimetryShift+nod high-precision spectroscopyDrift scan imaging


Commissioning tasks not requiring all mirror segments - acquisition strategies - software interfaces - focus, optical distortion, vignetting tests - wavelength calibration & stability - tracking & guiding stability

Commissioning tasks requiring all mirror segments - instrumental polarization calibrations - total sensitivity calibrations - final flatfield calibrations & variability - other aspects sensitive to pupil illumination


Calibration Issues

Wavelength: He, Ne, Ar, Cu lamps fed to diffuser before moving baffle

Flatfields: Continuum lamps fed to diffuser before moving baffle Flats taken next morning by re-creating actual science tracks w/baffle Observing scripts stored for easy reproduction (only a subset of spectrophotometric observations will need this

precision)

Observatory “superflats” created periodically in standard configurations -> enable differential flats taken on nightly basis

Stray/scattered light? TBD during commissioning




Documents

Oct 17, 2001SALT PFIS Preliminary Design Review1 Operation Concepts Definition Document (OCDD) Chip Kobulnicky University of Wisconsin