Instrument Science Report FGS-033
Cycle 6 FGS Calibration Plan
Lauretta M. Nagel, Olivia L. Lupie, Sherie T. Holfeltz
20 June, 1996
ABSTRACT
This is a summary of the FGS calibration observations in Cycle 6. Full descriptions of the
individual programs are given. It should be noted that the scheduling of all the described
visits may be considered tentative, as the scheduling priorities must place the GHRS and
FOS observations first in the Long Range Plan.
1. Introduction
The Astrometer FGS (FGS3) is operating normally, therefore the Cycle 6 Calibration
Plan contains the same standard monitoring tests as the previous cycles. During the second
Servicing Mission, the FGS in bay 2, formerly used for guiding only, will be replaced with
a spare FGS that has been refurbished. This replacement FGS will be called FGS2R. The
Cycle 6 Calibration Plan does not include FGS2R, but it does set up a baseline of observations against which FGS2R will be measured. A number of visits from this plan are
scheduled before and after the SMOV period; these observations will tell us if anything in
FGS3 has changed as a result of the Servicing Mission. As there is no planned large Secondary Mirror in connection with the second Servicing Mission movement, any change is
considered unlikely.
The programs included as part of the SMOV period will re-commission FGSs 1 and 3,
and will commission FGS2R for guidance only. These programs are discussed in the
SMOV documentation and will not be included here.
The ground-based data on FGS2R leads us to conclude that FGS2R may be a viable
candidate to replace FGS3 eventually as the Astrometer. However, any assesment of
FGS2R’s astrometric capabilities will be performed as part of next year’s Calibration Plan.
A summary of the calibration plan may be found in Table 1.
1
Proposal ID 6919: FGS Cycle 6: Three Points of Light
Plan
Reference Transfer Functions of the FGS standard star Upgren 69 (v = 9.6, B-V = +0.5)
will be obtained through the PUPIL and F583W filters at three positions near the center of
the field of view. Reference Transfer Functions (TFs) will also be obtained at the center of
the fov through the F5ND filter.
Purpose: To monitor the long-term temporal variation of the Transfer Function at 3 different positions in the FOV. Theoretical and semi-empirical models have been unsuccessful
in predicting changes in FGS #3. Therefore, we provide a grid of Transfer Scans which are
used directly to remove the instrument signature from target observations.
Description: Eighteen transfer scans of Upgren 69 will be obtained at each of three locations distributed azimuthally about the center of the field of view of FGS #3 for each of the
F583W and PUPIL filters. Thirty-five scans using the F5ND filter of Upgren 69 will be
obtained only at the central location. A modified (shorter) test consisting of PUPIL,
F5ND, and F583W measurements at one position will be performed after SMOV. Finally,
a contingency repeat of the full test may be required if a large SMOV mirror motion
occurs.
Fraction of GO/GTO Programs Supported: 75% GO, 44% GTO
Resources:
Observation: 4 external orbits for the standard Three Points, 2 external orbits for the
shortened version, plus 4 contingency external orbits.
Analysis: 0.08 FTE
Special Requirements: Each execution of this test should be performed in back-to-back
visits. This test should be performed early in Cycle 6 prior to SMOV. A modified (shorter)
test consisting of PUPIL, F5ND, and F583W measurements at one position will be performed after SMOV. Finally, a contingency repeat of the full test may be required if a large
SMOV mirror motion occurs.
Accuracy: The goal is to obtain S/N > 100. Signal to noise ratios greater than 50 are
required.
Products: The transfer functions will be used in pipeline data reductions. The results will
be presented in an ISR.
2
Proposal ID 6920: FGS Cycle 6: Monitor the Long Term Stability of FGS #3
Plan
Several stars in M35 will be observed repeatedly throughout the year on a (roughly)
monthly basis using the F583W filter.
Purpose: To characterize the geometric stability of FGS #3 and allow for estimates of the
differential corrections to the Optical Field Angle Distortion (OFAD) and plate scale calibrations. The temporal variations do not follow specific trends and are of order 1 milli-arcsecond on timescales of a month or less.
Description: Up to 30 observations per visit, using the F583W filter, will be made of targets in M35. This program is repeated approximately monthly and has two orientations.
This monitoring will continue after the Servicing Mission.
Fraction of GO/GTO Programs Supported: 75% GO, 88% GTO
Resources:
Observation: 9 external orbits
Analysis: The STAT has had the responsibility and the resources to analyse this test.
The necessary OFAD and Long Term Stability (LTSTAB) software and expertise may be
acquired over the course of the next year. Otherwise, this requires 0.3 FTE.
Special Requirements:
Accuracy: 2.7 milli-arc-seconds RSS
Products: OFAD and plate scale coefficients will be used in pipeline calibrations and
data reductions, and for trend analysis.
3
Proposal ID 6921: FGS Cycle 6: Intermediate Plate Scale
Plan
Several stars in NGC 2516, including an asterism observed expressly for this purpose by
HIPPARCOS, will be observed through the F583W filter four times over the next year.
Purpose: To provide the plate scale which is used in conjunction with the OFAD to reduce
POS mode observations. Three to four HIPPARCOS stars will be used to determine the
plate scale to an accuracy of 0.5 mas/arc-minute within the central region of the FOV.
Multiple observations are needed to monitor plate scale changes and to accomodate any
Servicing Mission-related changes.
Description: Up to 30 observations of targets within NGC 2516 will be made per visit
using the F583W filter. All of the targets, including reference stars, will be positioned in or
very near the central 4 x 5 arc-sec “football” region of the pickle. The target field will be
visited four times in the next year. Three repetitions will be performed prior to SMOV,
with one more performed after SMOV.
Fraction of GO/GTO Programs Supported: 75% GO, 88% GTO
Resources:
Observation: 4 external orbits
Analysis: 0.3 FTE
Special Requirements: This program will require certain ORIENT angles to optimally
position the targets in the central region of the field of view.
Accuracy: The goal is to obtain a measure of the plate scale which is accurate to 0.5 mas
per arc minute.
Products: The plate scale will be used in pipeline calibrations and data reductions and in
trend analysis. The results will be presented in an ISR.
4
Proposal ID 6922: FGS Cycle 6: Blue TF Calibration
Plan
Reference Transfer Functions (TFs) will be obtained through the PUPIL, F583W, and
F5ND filters at the center of the field of view for targets B-V color index < 0.5 mag.
Purpose: To acquire Transfer Function data on a set of blue stars. The Transfer Function
varies in lobe structure, and full-width half-maximum as a function of wavelength. Color
indices of -0.1 to +1.9 can produce variations in full-width half-maximum of up to 1015%. These color transfer scans will form the basis of a grid from which the GO can select
the closest configuration to the target characteristics. The appropriate TF will then be used
to remove the instrument signature from the target observations.
Description: Fifteen transfer scans of LAT-COL-1B (v = 9.6, B-V = +0.18) will be
obtained with each of the PUPIL and F583W filters at the center of the field of view of
FGS #3. Thirty transfer scans of HD 28149 (v = 5.5, B-V = -0.1) at the center of the fov
will be obtained using the F5ND filter.
Fraction of GO/GTO Programs Supported: 75% GO, 44% GTO
Resources:
Observation: 2 external orbits.
Analysis: 0.04 FTE
Special Requirements: Both visits should be grouped within 3 days or so.
Accuracy: The goal is to obtain S/N > 100. Signal to noise ratios greater than 50 are
required.
Products: The transfer functions will be used in pipeline data reductions. The results will
be presented in an ISR.
5
Proposal ID 6923: FGS Cycle 6: Red TF Calibration
Plan
Reference Transfer Functions (TFs) of red stars will be obtained through the PUPIL,
F583W and F5ND filters at the center of the field of view.
Purpose: To acquire Transfer Function data on a set of red stars. The Transfer Function
varies in lobe structure, and full-width half-maximum as a function of wavelength. Color
indices of -0.1 to +1.9 can produce variations in full-width half-maximum of up to 1015%. These color transfer scans will form the basis of a grid from which the GO can select
the closest configuration to the target characteristics. The appropriate TF will then be used
to remove the instrument signature from the target observations.
Description: Fifteen transfer scans of LAT-COL-1A (v = 9.7, B-V = +1.9) and SAO
185689 (v = 9.3, B-V = 1.5) will be obtained through each of the PUPIL and F583W filters at the center of the field of view of FGS #3. Thirty transfer scans will be obtained with
the F5ND filter at the center of the field of view for HD 59149( v = 6.7, B-V = 1.3) and
HD 28484 (v = 7.9, B-V = 1.7).
Fraction of GO/GTO Programs Supported: 75% GO, 44% GTO
Resources:
Observation: 4 external orbits.
Analysis: 0.04 FTE
Special Requirements: All four visits should be grouped within 3 days or so.
Accuracy: The goal is to obtain S/N > 100. Signal to noise ratios greater than 50 are
required.
Products: The transfer functions will be used in pipeline data reductions. The results will
be presented in an ISR.
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Table 1: FGS Cycle 6 Calibration Plan
Estimated Time (orbits)
ID
Proposal Title
Frequency
“External”
“Internal”
Required
Resources
(FTE)3
Products
Accuracy
S/N>50
Notes
Routine Monitoring Programs
6919
3 Points of Light
2
1
6
1
F583W, PUPIL, F5ND
0
0.08
Pipeline
Pipeline
Pipeline
0.5 mas/
arc-min
F583W
F583W,PUPIL,F5ND
6920
Long Term Stability Test
9
9
0
0.32
6921
Intermediate Plate Scale
4
4
0
0.32
3 mas/axis F583W
6923
Red Transfer Functions
1
4
0
0.04
Pipeline
S/N>50
6922
Blue Transfer Functions
1
2
0
0.04
Pipeline
S/N>50 F583W,PUPIL,F5ND
25
0
0.76
TOTAL TIME (including all executions)
NOTES:
1
An additional full repetition (4 orbits) may be needed if there is a large SMOV mirror
move.
2 Assumes availability of STAT support.
3 Required Resources does not include modelling or extensive analysis.
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Special Calibration Programs