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Cycle 5 Calibration Summary and Description

GHRS Instrument Handbook


The table on the next page and the sheets that follow provide a summary of our Cycle 5 calibration plan.

Table 5.1: Proposed GHRS Cycle 5 Calibration Plan


Program 6168: GHRS PHA/Ion/Threshold Adjustment Tests--Cycle 5

Purpose: The purpose of this test is to determine the optimal threshold settings for the GHRS detector diodes.

Description: This internal test performs a pulse height analysis to determine individual diode response as a function of threshold for GHRS detectors 1 and 2. Based on this evaluation new thresholds may be determined for optimal GHRS operation. Also included is one ion test which is a PHA of twice normal threshold to look for ion events (which accelerate back up the 22 kV potential of the tube, liberate electrons from the photocathode, and produce events of twice normal energy (this should be a very low, stable rate)).The final test will determine the optimal, non-standard discriminator thresholds for the few anomalous channels on both detectors. A 15 second flat field observation followed by a 210 second dark count is performed at each of 10 discriminator threshold values for each detector. Cross-talk tables are disabled at the start of this test and re-enabled at the end.

This test will execute once during Cycle 5.

Fraction of GO Programs Supported: This test supports 100% of GHRS observations.

Time needed: Internal-6 orbits (3 for each detector).

Program 6169: GHRS Cycle 5 Echelle Wavelength Monitor

Purpose: The purpose of this test is to determine the dispersion solution for the GHRS echelle gratings over the full range of wavelengths covered by the echelles.

Description: This test is an internal test which makes measurements of the Pt-Ne spectral calibration lamp SC2. The spectra obtained are used to calibrate the carrousel function, Y-deflection function, resolving power sensitivity, and scattered light. This proposal defines the spectral lamp test for both Ech-A and Ech-B.

This test will executed every 4 months during Cycle 5 for a total of 3 times.

Fraction of GO Programs Supported: This test supports all echelle observations (37% of all GHRS observations).

Time needed: External-12 orbits (3 orbits for both echelles, 4 times in the cycle).

Special Requirements: Some wavelengths are out of the nominally useful range but are used in determining the calibration.

Accuracy Requirement: 1 diode RMS for pipeline calibrated wavelengths.

Program 6170: GHRS Echelle and G140M Long-term Monitor--Cycle 5

Purpose: The program contains a series of observations to monitor the long-term (time-scale: 1 year) sensitivity of Ech-A, Ech-B, and G140M.

Description: This proposal defines a series of observations that will continue the long-term monitor of Ech-A, G140M, and Ech-B. Ech-A and G140M observations will be made both through the LSA and the SSA. Ech-B observations are through the LSA only. m Col is used for all observations. For the echelles, OSCAN observations will measure the sensitivity near the blaze peak. The setups for Ech-B are chosen to be the same as those used in the Science Verification period, to be able to compare directly to the original calibrations. WSCAN observations will scan across m=20 in Ech-B. Ech-A is used with an OSCAN at the blaze peak (ml =56100), plus one WSCAN. G140M is used at 1100, 1200, 1300, 1400, 1500, and 1600 Å.

Instrument Configurations:

GO Programs Supported: GHRS programs using Ech-A (19%), Ech-B (18%), and G140M (17%).

Time needed: Total of 6 orbits, 3 orbits for Ech-A + G140M, and 3 orbits for Ech-B.

Special Requirements: There are no stringent special requirements. We only request that the observations be executed in the middle of Cycle 5 (to within about 2 months).

Accuracy: The goal of this program is to monitor and document the long-term behavior of the echelle and G140M sensitivities. The sensitivities found in this program will be compared to previous measurement obtained for the same star and with the same instrument configuration The relative accuracy should be at least 2%.

Products: The results of the test will be documented in an Instrument Science Report. The ISR will be published within two months of completion of the program. Database updates will only be performed if anomalies are detected.

Program 6171: CRIMP1--Cycle 5 Condensed-Regimen Integrated Monitoring Program for Side 1 of the GHRS

Purpose: The program monitors the sensitivity, wavelength and detector calibrations of Side 1 at a rate of 4 times per year.

Description: 4 times per year, the following observations will be done:

All observations are with the LSA or the SC2 aperture.

GO Programs Supported: GHRS programs using gratings G140M (17%) and G140L (44%) for wavelengths and sensitivities. The detector calibration part supports Ech-A (19%) in addition to G140L and G140M.

Time needed: Total of 24 orbits (6 orbits per execution).

Special Requirements: One complete set of observations (detector, sensitivity, and wavelength) should be on one SMS. The detector calibrations themselves should be executed within 24 hours. The 3 repeats should occur should occur every 9 or 10 days.

Accuracy: The primary goal of this program is to check for anomalies in basic GHRS properties and calibrations. Sensitivities are regarded as anomalous if they differ from past measures by more than 2%. Dark measures should fall within the bounds of previous observations. Wavelength monitoring is done to build the database upon which the wavelength calibration program is based.

Products: The results of the test will be documented in an Instrument Science Report. The ISR will be published 2 months after completion of the program. Database updates will only be performed if anomalies are detected.

Program 6172: CRIMP2--Cycle 5 Condensed-Regimen Integrated Monitoring Program for Side 2 of the GHRS

Purpose: The program monitors the sensitivity, wavelength and detector calibrations of Side 2 at a rate of 4 times per year.

Description: 4 times per year, the following observations will be done:

GO Programs Supported: GHRS programs using gratings G160M (31%), G200M (12%), and G270M (26%).

Time needed: Total of 44 orbits. 11 orbits per execution.

Special Requirements: As for CRIMP1.

Accuracy: As for CRIMP1 (6171).

Products: The results of the test will be documented in an Instrument Science Report. The ISR will be published 2 months after completion of the program. Database updates will only be performed if anomalies are detected.

Program 6209: Cycle 5 G140L Photocathode Granularity Determination

Purpose: To obtain a flat field for the G140L grating over a range of photocathode positions.

Description: The object of this program is to map artifacts on the surface of the photocathode due to granularity for the G140L grating. Locations of anomalous areas of the photocathode response will be determined by obtaining spectra of standard star HD93521 centered in the LSA and the SSA. The GHRS will be commanded in WSCAN mode and a series of spectra will be obtained from different positions on the digicon faceplate, the photocathode. This program need only be executed once at the start of Cycle 5.

Instrument Configuration: Side 1, G140L, LSA & SSA

GO Programs Supported:40 GHRS Cycle 5 programs (about 44%).

Time needed: 4 orbits.

Accuracy: The G140L flat field is needed to remove the effects of instrumental blemishes (small scale irregularities on the detector face plate and photocathode) from spectra with reasonable signal-to-noise (S/N ~50). The flat field will allow observers with good S/N to achieve 2% photometric precision for their data.

Products: The results for this program will be documented in an Instrument Science Report (ISR) and published after completion of the program. The flat field will be delivered to CDBS for delivery to OPUS.

Program 6210: GHRS Scattered Light Test-Cycle 5

Purpose: To measure of the scattered light within 3 arcsec of the GHRS Small Science Aperture.

Description: The object of this program is to measure the PSF from a point source in the SSA at various distances from the SSA. Thus, this is a combination PSF/scattered light test in that we measure the PSF at several different radii and at the same time obtain a measure of the contributed scattered light from nearby objects. This test will be carried out at two wavelengths, 2250 Å and 3050 Å, and will be used in conjunction with an SMOV test at 1450 Å to characterize the scattered light for GHRS.

This program need only be executed once during Cycle 5.

Fraction of GO Programs Supported: This test will be used for close-out and archival purposes and supports some Cycle 5 GO programs as well.

Time needed: External-4 orbits.

Special Requirements: None.

Accuracy: The accuracy goal of this test is 2% absolute for each measured point in the PSF.

Products: The results for this program will be documented in an ISR and published within 2 months after completion of the program.

Program 6212: GHRS Cycle 5G140M Sensitivity Characterization

Purpose: To determine the sensitivity and vignetting for grating G140M.

Description: This program observes a standard star to measure the sensitivity of G140M over its full wavelength range. Spectra are obtained with overlapping centers to make it possible to determine vignetting as well. The standard star m Col is observed with both the LSA and SSA in WSCAN mode. This program is to be executed only once at the start of Cycle 5.

Instrument Configuration: Side 1, G140M, LSA & SSA.

GO Programs Supported: 15 Cycle 5 GHRS programs (about 17%).

Time needed: 3 orbits.

Accuracy: Sensitivities are accurate to about 10% on an absolute scale. We will monitor G140M sensitivity in the future as well.

Products: The results from this program will be documented in an Instrument Science Report approximately 12 weeks after the observations are obtained. Calibration reference files will be delivered to OPUS at that time.

Program 6213: GHRS Aperture Offsets--Cycle 5

Purpose: The purpose of this test is to measure the relative wavelength offset between the LSA and SSA apertures for all gratings.

Description: While measurements of the relative offsets between SC1/SC2 and the SSA were made prior to launch, no such measurements were made for the LSA. During OV/SV some measurements were obtained but they provided minimal results for the Side 2 first-order gratings only. While it has always been recommended that observers use the SSA to obtain the best wavelengths, this test will provide LSA observers with better pipeline-calibrated wavelengths for their observations.

The strategy is to observe at a series of carrousel positions across each grating (order) in the LSA and SSA, taking a WAVECAL spectrum before each object spectrum. The wavelength coverage is needed as the pre-launch calibrations were found to vary nonlinearly with wavelength. Exposure times are the minimum exposure time for the default STEPPATT which should give a minimum signal-to-noise of about 20.

This test will execute once during Cycle 5.

Fraction of GO Programs Supported: This test supports all LSA observations.

Time needed: External-16 orbits.

Special Requirements: None.

Accuracy Requirement: 1 diode RMS for wavelengths in the LSA.

Table 5.1: - Proposed GHRS Cycle 5 Calibration Plan
Program 6168: GHRS PHA/Ion/Threshold Adjustment Tests--Cycle 5
Program 6169: GHRS Cycle 5 Echelle Wavelength Monitor
Program 6170: GHRS Echelle and G140M Long-term Monitor--Cycle 5
Program 6171: CRIMP1--Cycle 5 Condensed-Regimen Integrated Monitoring Program for Side 1 of the GHRS
Program 6172: CRIMP2--Cycle 5 Condensed-Regimen Integrated Monitoring Program for Side 2 of the GHRS
Program 6209: Cycle 5 G140L Photocathode Granularity Determination
Program 6210: GHRS Scattered Light Test-Cycle 5
Program 6212: GHRS Cycle 5 G140M Sensitivity Characterization
Program 6213: GHRS Aperture Offsets--Cycle 5