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GHRS Advisories

Advisory for users of the 'poffsets' task. 12/98

The 'poffsets' task is used to determine spectral shifts and produces a table used as input to the task 'specalign'. This task is used, for example, with GHRS FP-SPLIT data, although it is not instrument specific. In FP-SPLIT mode, the same spectrum is observed several times at slightly shifted pixel positions. The specalign task will combine the spectra using the wavelength offset information determined by 'poffset'.

The 'poffsets' task in its default mode is working properly if the input spectra have REASONABLY STRONG SPECTRAL FEATURES AND S/N > 30. The default mode of poffset uses a cross correlation technique to determine wavelength offsets between individual spectra from spectral features. If the features are too weak or noisy, the cross correlation technique will generate unreliable results. 'poffsets' should only be used in the default mode (i.e., explicit cross correlation of fluxes) after careful consideration of the data. In order to make sure that the best possible results are obtained, it is a good idea to run the task in BOTH the default mode, and the mode (i.e., "usecorr=no" for 'poffsets') which does not perform a cross correlation, but rather uses the wavelength information to determine predicted offsets.

Calibration Product Review for the GHRS. 09/97

The tables in this document provide a history (as of 1 Jul 1997) of the differences among the reference images and tables which were used by the Post Observation Data Processing System (PODPS) to calibrate GHRS data. This document can be used to fill in information that the Starview GHRS Reference file screen may not be able to provide.

Implementation of a Background Count Rate Model for the GHRS. Jun 97

CALHRS has been enhanced to allow users to choose to subtract a background model rather than observed background. Please read the Instrument Science Report for more details. The Calibration Product Review has been updated to reflect the additional files available.

Decreases in GHRS far UV Sensitivity. 06 Jun 97

Please read this information if you have post-COSTAR data between 1100Å and 1200Å. New post-COSTRAR G140L Sensitivity files are available in CDBS. The Calibration Product Review has been updated to reflect the additional files available. Also see GHRS-ISR-085.

Multigroup G140L Flat-field files. Mar 97

We recently noticed that the first and last points of the multigroup G140L flat-field files in CDBS (ga41342hz.r1h and ga41342iz.r1h) are INDEF instead of 1. and thereby cause a slight problem when used to calibrate one's data. New files (h3e1400fz.r1h and h3e1400gz.r1h) have been put into CDBS to correct the problem.

ZWAVECAL and Side 1 Data. Jan 97

We have recently noticed that using zwavecal on post-COSTAR Side 1 observations (i.e., gratings G140L, G140M, and Echelle-A) will cause an error due to the apparent carrousel position being out of range. This comes about because the Side 2 electronics are being used to drive the carrousel for both Side 1 and Side 2 gratings. We are considering several possible ways to fix this problem, and we will post a notice on our web advisories page when we learn more. If you encounter errors using the zwavecal task, please contact help@stsci.edu.

Photocathode Granularity Maps for G140L. 10/96

Flat field files for use with GHRS G140L data are now available from the Calibration Database (CDBS) and the archive. ISR-076 gives details of when it is appropriate to recalibrate your data with the new flat field files (photocathode granularity maps). The new files are not intended for installation into the Routine Science Data Processing (RSDP) pipeline.

SSA PEAKUPs with Mirror-A1. 18 Jun 96

In an effort to safeguard against poor centering in the SSA for observations using Mirror-A1, overheads are being increased in Cycle 6 programs. Please read this advisory for more details.

FOS-assisted ACQs and wavelength accuracy. 18 Mar 96

This is a description of the wavelength accuracy one can expect with FOS-assisted GHRS target acquisitions. Please read this if you need accurate wavelengths and are using FOS for your target acquisition. It has also been added to the proposal writing FAQ pages.

Problems found with calibrated data. Oct 95

On October 8, 1995, the OPUS group at STScI reported seeing an anomaly in some reduced data. We traced the problem and notified GOs whose data was affected. Please read this complete description of and solution to the problem.

Observations taken between 29 May and 24 Jun 1995 were INCORRECTLY calibrated.

As of 11 Aug 95, these observations have been reprocessed and are now correct in the archive. Please read this if you recieved data between 29 May and 24 Jun 1995.

SYNPHOT throughput tables incorrect. 31 Aug 95

If you have used SYNPHOT to estimate target acquisition counts for your proposals please read this notice.

The MAXWAVE keyword is incorrect for FP-SPLIT data. Aug 95

This minor problem affects only FP-SPLIT data headers. Observation Problem Report 29540 was filed and CALHRS v.1.3.9 corrects the problem.

SSA Peakups in Mirror A1. 1 Jun 95

Inconsistent behavior of A1 SSA peakups leads to suggestions for improvement. Please read for more information.

Side 1 Flaky Diode (.gif). May 95

Diode 85 (out of 500; 91 out of 512) is periodically seen to have a low response. You may want to look at your Side 1 data carefully in this area. This diode was turned off on 29 May 95.

Side 2 Noisy diode (.gif). May 95

Sporadic noise in diode 237 (out of 500; 243 out of 512) seen in observations 2nd and 3rd weeks of Mar 95. You may want to look at your data carefully in this area. This diode was turned off on 15 May 95.

Incorrect Count Rates Using SYNPHOT. Apr 95

Please read this article that appears in April 95 issue of GHRS STAN if you use SYNPHOT.

New Flight Software: Timeout Fix. Apr 95

New flight software has been added to decrease the amount of data lost due to carrousel resets. Please read this article in the April issue of the GHRS STAN.

Identification of Erroneous Doppler Compensation for Moving Targets. July/Nov 94

Contains update of notice sent to PIs with GHRS Moving Target observations. Informs them of a problem with the Doppler Compensation for Moving Targets, and that there is now an algorithm to recover from the problem.

Updates for Users of the GHRS in Cycle 4 and prospective Cycle 5 proposers. 20 July 1994

Contains status report on GHRS operations, including hints on G140L usage and other suggestions for writing Cycle 5 proposals. A must read for Cycle 5 proposers.