-------------+--------------------------------------------+--------------------- | GGGGGGG HH HH RRRRR SSS | STScI | GG HH HH RR R SS | STAN - GHRS Analysis | GG GGG HHHHHH RRRRR SS | Number 15 News | GG GG HH HH RR R SS | August 1996 | GGGGGGG HH HH RR R SSS | -------------+--------------------------------------------+--------------------- CONTENTS: - GHRS NEWS + Throughput Changes + Background and Dark Measurements + Paper Products - NEW GHRS DOCUMENTATION + ISR-076: G140L Flat Fields - RECENT PREPRINTS - APPENDIX: GHRS CONTACTS ================================================================================ Throughput Changes ------------------ We remind observers that we have seen changes in the absolute throughput of the GHRS since the 1993 Servicing Mission. Above Lyman-alpha these changes have reached about 4% net over two years, which is less than the uncertainty in absolute fluxes. However, below Lyman-alpha the decline is more significant, and amounts to 30 to 40% at the shortest wavelengths. If your observations include wavelengths below Lyman-alpha, and absolute fluxes at those wavelengths are important for your science, please contact your Contact Scientist or help@stsci.edu so that we can determine an appropriate flux correction for when your data were taken. A detailed analysis is in progress so that GOs and ARs can make these corrections themselves. Background and Dark Measures ---------------------------- Your GHRS observations normally include measurements of the background seen at the time of observation. This is done with either the science diodes or the corner diodes, depending on the STEP-PATT chosen (see the Instrument Handbook for details). For short (see Table 1 below) observations, the count rate seen is so low that the statistical accuracy of the dark determination is poor. Corner diodes are usually worse than science diodes for measuring backgrounds but are preferable when scattered light contaminates the interorders, such as for certain echelle observations. However, CALHRS currently interpolates between the means of the right and left corner diodes instead of averaging all 4 together to get a constant. Therefore, we now recommend that users ignore the background calculated by CALHRS for STEPPATTs 1-3, 8, 9, 14, and 15. As an alternative to these 2 situations, for observations which do not pass through the SAA, we will implement a model for the background counts developed by Don Lindler that predicts the dark rate from the geomagnetic position at the time of the observation, and will advise when that is available. In the mean time, that model is described on p. 216 of Calibrating Hubble Space Telescope: Post Servicing Mission. If you have questions about dark/background measurements, please contact help@stsci.edu. Table 1: Stepping Quarter Half STEPPATTs: (Odd**) (Even) Detector 1 less than 16 min less than 8 min Detector 2 less than 30 min less than 16 min ** except STEPPATT=1 which has NO sub-stepping. Paper Products -------------- The GHRS Group has just begun to review standard paper products that will be included with all GO observations. We anticipate that GOs will start receiving these paper products for observations made after September 1. These sheets provide a quick summary of vital statistics of the observation and some useful graphical information. ================================================================================ NEW GHRS DOCUMENTATION ---------------------- G140L Flat Fields ----------------- An Instrument Science Report is now available about flat fields for exposures made with grating G140L. To request the full report, send email to help@stsci.edu requesting GHRS-ISR-076. ================================================================================ RECENT PREPRINTS ---------------- We draw your attention to these papers, based on GHRS data, that will appear in the next few months. This list includes all preprints received by the STScI Library not yet published in the journals. Please remember to include our Library in your preprint distribution list. COWAN, J.J.; SNEDEN, C.; TRURAN, J.W.; BURRIS, D.L.; MCWILLIAM, A.; PRESTON, G.W. "R- and S-process signatures in metal-poor halo stars" Nucl. Phys. A accepted LEITHERER, C. "Spectral synthesis analysis of hot-star populations" Liege Colloq. 33 PISKUNOV, N.; WOOD, B.E.; LINSKY, J.L.; DEMPSEY, R.C.; AYRES, T.R. "Local interstellar medium properties and deuterium abundances for the lines of sight toward HR 1099, 31 Comae, beta Ceti, and beta Cassiopeiae" ApJ accepted WOLVEN, B.C.; FELDMAN, P.D.; STROBEL, D.F.; MCGRATH, M.A. "Lyman-alpha induced fluorescence of H2 and CO in HST spectra of a comet Shoemaker-Levy 9 impact site on Jupiter" ================================================================================ APPENDIX: GHRS contacts ----------------------- Any questions about the scheduling of your observations should be addressed to your Program Coordinator. Post-Observation questions can be addressed to your Contact Scientist. Analysis, STSDAS or any other questions can also be addressed to help@stsci.edu. ================================================================================ To subscribe or unsubscribe send a message to listserv@stsci.edu with the Subject: line blank and the following in the body: [un]subscribe ghrs_news YOUR NAME ================================================================================ Comments, questions, suggestions, etc. can be e-mailed to help@stsci.edu ================================================================================ The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. ================================================================================