-------------+--------------------------------------------+--------------------- | FFFFFF OOOOOO SSS | STScI | FF OO OO SS | STAN - FOS Analysis | FFFF OO OO SS | Number 9 News | FF OO OO SS | March 1996 | FF OOOOOO SSS | -------------+--------------------------------------------+--------------------- CONTENTS: - FOS NEWS + New Calibration Procedures and Products + Modification to "calfos" + More on Background and Scattered Light Subtraction + Caution to Observers Measuring Coordinates from WFPC2 Early Acquisition Images + New FOS Team Member - The On-Line Calibration Database Astronomical Library - Tape Recorder #2 Failure - Data Analyst Position Available at STScI - RECENT PREPRINTS - APPENDIX: FOS CONTACTS ================================================================================ New Calibration Procedures and Products ---------------------------------------- We have released to the user community our new Average Inverse Sensitivity (AIS) reference files and the tables needed for Post-COSTAR calibrations. >From 0h UT 19 March 1996, all STScI FOS data will have these as the default (pipeline) calibration. The files are also available on STEIS in the directory cdbs/cdbs, (in either yref for images, or ytab for tables). We list the detector/grating combinations for the AIS files (which are images) below: POST-COSTAR AIS file Grating Detector fac0835my.r8h(d) g190h RED fac0835ny.r8h(d) g270h RED fac0835py.r8h(d) g400h RED fac0835qy.r8h(d) g570h RED fac0835ry.r8h(d) g780h RED fac0835sy.r8h(d) g160l RED fac0835ty.r8h(d) g650l RED fac08360y.r8h(d) prism RED fac08361y.r8h(d) g130h BLUE fac08362y.r8h(d) g190h BLUE fac08363y.r8h(d) g270h BLUE fac08364y.r8h(d) g400h BLUE fac08366y.r8h(d) g160l BLUE fac08367y.r8h(d) prism BLUE fac08368y.r8h(d) g570h BLUE The following tables apply to *all* Post-COSTAR FOS AIS calibrations: fad1554cy.cya g1512585y.cyb fad1554hy.cyc fad1554ky.cyd New Pre-COSTAR AIS reference files and the accompanying tables have also been delivered in February 1996. These files are found in the same STEIS directories as the Post- COSTAR files. COSTAR files. PRE-COSTAR AIS file Grating Detector g2t14397y.r8h(d) g190h RED g2t14399y.r8h(d) g270h RED g2t1439by.r8h(d) g400h RED g2t1439cy.r8h(d) g570h RED g2t1439ey.r8h(d) g780h RED g2t1439gy.r8h(d) g160l RED g2t1439hy.r8h(d) g650l RED g2t1439jy.r8h(d) prism RED g2t1439ky.r8h(d) g130h BLUE g2t1439ly.r8h(d) g190h BLUE g2t1439ny.r8h(d) g270h BLUE g2t1439oy.r8h(d) g400h BLUE g2t1439ry.r8h(d) g570h BLUE g2t1439py.r8h(d) g160l BLUE g2t1439qy.r8h(d) prism BLUE The tables that apply for *all* Pre-COSTAR AIS files are: g310947py.cya g3109480y.cyb g3109483y.cyc g3109487y.cyd Modification to "calfos" ----------------------- It was recently found that "calfos" had a small, but rather serious bug in the portion which calculates the amount of scattered light. To explain; where we have unilluminated diodes (i.e. those diodes with zero sensitivity to dispersed light) in a spectrum, we use these to estimate the amount of scattered light in the spectrum. This was previously done by simply calculating the mean of the countrate in the unilluminated and subtracting this number, in a wavelength-independent way, from the the spectrum. It turns out that this method is subject to the rare, but possible problem of a cosmic-ray hit on the unilluminated portion of the diode array that would then artificially raise the scattered light level subtracted from the spectrum. This bug has been fixed for the next release of STSDAS, but in the meantime, the work-around to this problem is the following: Use the task "fixpix", and then recalibrate. cl> grlist ynnnxxxxx.d0h - > y_data_list cl> print ("c1 c2 1 1", > "y_data_fixpix_list") cl> fixpix @y_data_list y_data_fixpix_list cl> calfos ynnnxxxxx y_data_fixed The "print" statement above creates the input file needed by the "fixpix" task. The format of the file is a series of lines which define a bad "region" in the input images: start_column end_column start_line end_line So, for FOS data with a noisy diode affecting pixels c1 through c2, the above input is needed. The "fixpix" tasks operates on the image in-place. If one wants to preserve the original data, a copy will need to be made. "fixpix" will interpolate between the pixels immediately outside the bad range and replace the bad range with the interpolation. In addition there is a single look-up table that is required to run the scattered light correction within "calfos". This table is available from STEIS in the directory /cdbs/cdbs/ytab, and is called e3i09491y.cy9. The table is to be used for both Pre- and Post-COSTAR data. As a further caveat, only "calfos" version 2.4 and later, will have the fix mentioned above, along with default settings to use the AIS method and the scattered light corrections mentioned in this note. Queries on how to obtain this latest version of "calfos" should be directed to help@stsci.edu. A further discussion of the background and scattered light phenomena follows. More on Background and Scattered Light Subtraction -------------------------------------------------- by Anuradha Koratkar The low sensitivity regions of some FOS gratings are affected by grating scattered photons and need to be corrected whenever possible. Yet, before this scattered light correction can be done, a proper background subtraction *must* be done. For some detector/grating combinations one can check if the pipeline has correctly accounted for the background + scattered light. For the combinations listed below, there is a region where the diodes are not illuminated (i.e. dark pixels) by the grating. These detector/grating combinations, along with the range of pixels unilluminated for standard quarter-stepped spectra are: Detector Grating Range (pixels) Beginning Ending Blue G130H 30 129 Blue G570H 1300 1999 Blue G160L 900 1199 Blue Prism 1860 2059 Red G190H 2040 2059 Red G780H 10 149 Red G160L 600 899 Red G650L 1100 1199 Red Prism 0 899 Note that although G190H, and G270H on the blue side suffer from scattered light, it is difficult to correct for it in the calibration pipeline. The The scattered light tool in STSDAS, "bspec", is a useful way of gauging just how much scattered light one can expect in a spectrum, given the detector/grating combination. For typical FOS observations, the background correction (essentially the dark count correction) is done in the "calfos" pipeline. This correction uses the appropriately scaled background to account for the location of the spacecraft in the earth's magnetic field. This predicted background count rate is stored in the c7h file. The background is frequently underestimated, and one way to check this is to compare the c7h file with the c4h file in the unilluminated pixel region. Note that these unilluminated pixels show not only the background count rate, but also the scattered light. For the detector/grating combinations which have unilluminated pixels, the calibration pipeline is used to correct for the excess background *and* scattered light. This is done by averaging the count rate in the unilluminated pixels and subtracting this from the data. (Unfortunately, this process is called scattered light correction in the "calfos" pipeline.) If this scattered light correction is done correctly, the c5h file should have zero count rate in the unilluminated pixels. As noted in the previous article, the scattered light correction technique has a problem if there are noisy diodes in the dark pixel region. In this case the average count rate in the unilluminated pixel region is higher than observed, and the scattered light correction is overestimated. To correct this problem, a new scattered light correction will be implemented in "calfos" 2.4 and later versions. In this technique, those unilluminated pixels which have count rates 4-sigma higher than median are eliminated. Next, the average count rate in the remaining unilluminated pixels is calculated, and subtracted from the data. This fix to the pipeline version of "calfos" went into effect 19 March 1996. GOs are advised to compare their intermediate calibration files to determine if the background and scattered light corrections have been done properly *before* any analysis with "bspec" is carried out. Caution to Observers Measuring Coordinates from WFPC2 Early Acquisition Images ------------------------------------------------------------------------------ GOs who use the metric task in stsdas.hst_calib.wfpc to measure target coordinates from a WFPC2 early acquisition image for subsequent FOS and GHRS observations should be cautioned to check which version of STSDAS is currently installed. Older versions of the metric task will produce incorrect results for WFPC2 data. STSDAS version 1.3.2 (August 1994) and earlier versions contain the plate solutions for WF/PC-1 only, and will therefore return incorrect coordinates for WFPC2. The metric task in STSDAS V1.3.2 and earlier returns correct coordinates for WF/PC-1 but returns coordinates off by up to 60 arcseconds if applied to WFPC2 images. The error depends on which chip the target is located, but can be as large as 60" for PC1, 0.1" for WF2, 5.6" for WF3, and 7" for WF4. If earlier versions of metric are used on WFPC2 data, the errors can cause the FOS or GHRS acquisition to fail, and the observations will be lost. We would also like to remind users that metric must be run on individual chips, not on a mosaiced image. The most current version of STSDAS is 1.3.4 (October, 1995). We recommend that all users upgrade to this version to obtain the most accurate results. Lastly the FOS team would like to note that the quality of the "metric" derived coordinates are only as good as the GSC coordinates for the Guide stars used for the WF/PC or WFPC2 images. If target co-ordinates are derived *solely* from "metric" measures, without any further tie-ins to the GSC frame, the FOS team recommends that a more robust initial stage of target acquistion, than is described in FOS Instrument Handbook V6, be used. Specifically, an 2x6 ACQ/PEAK with STEP-SIZE-X=3.3 and STEP-SIZE-Y=1.2 should be prepended to the the target acquistion sequence. New FOS Team Member ------------------- We welcome Alex Storrs as a new Instrument Scientist to the FOS group. Alex comes from the PRESTO (program development and implementation) group at STScI, and brings to us a much-needed expertise in both planetary science and moving targets observations. ================================================================================ The On-Line Calibration Database Astronomical Library ------------------------------------------------------ by Luis Colina and Krista Rudloff Several atlases consisting of both observed and model stellar catalogs as well as HST standard stars spectra are available on-line. The atlases form a fundamental database needed for several HST related activities. For instance, the atlases provide absolute standards for the calibration of HST instruments, model spectra to cover spectral ranges not available from observations, a uniform database for use with software tools such as the exposure time simulators for FOC, WFPC2, and NICMOS, and a database for use with applications such as SYNPHOT. The on-line library includes: - Atlases of HST Standard Stars * CALSPEC (composite UV and optical absolute flux calibrated reference spectra of the HST standards on the white dwarf scale) * CALOBS (original and updated versions of the UV and optical spectra of the standards) - Atlases of Spectrophotometric Stellar Spectra * Bruzual * Jacoby-Hunter-Christian * Gunn-Stryker * Bruzual-Persson-Gunn-Stryker - Atlases of Stellar Model Atmospheres * Buser-Kurucz * Kurucz's 1993 atlas (new) The atlases, along with descriptions, may be accessed at the URL: http://www.stsci.edu/ftp/instrument_news/Observatory/astronomical_catalogs.html ================================================================================ Tape Recorder #2 Failure ------------------------ On 19 Jan 1996, the #2 tape recorder failed on-board. While serious, it will not impact most science observations as this recorder was used for the engineering data. It will impact all engineering data for ~17 minutes of each orbit in that HST will have engineering telemetry gaps. So if something does go wrong with an observation during that time, there will be no engineering data for analysis. This also means that products like the Jitter (Observation Log) files will be incomplete. The gaps are caused by the incomplete coverage of the TDRSS satellite network on the HST orbit. Due to a "bit slip" problem from last year, this tape recorder is currently on the list of items to be replaced during the 1997 Servicing Mission. It will be replaced by a "solid state recorder" which will vastly increase the onboard data storage capacity of HST and will allow engineering data to be recorded during any TDRS gaps. ============================================================================== Data Analyst Position Available at STScI ---------------------------------------- The Space Telescope Science Institute anticipates several openings for Data Analysts. Data Analysts in the Science Support Division help General Observers and Archive Researchers analyze HST data, work with Instrument Scientists in calibrating the HST instruments, and work with STScI staff on grant-supported research projects. These research projects span a range of size scales from comets and planets to the large scale structure of the universe and a range of wavelengths from radio to X-ray astronomy. Applicants should possess a B.S. degree in astronomy or physics, or equivalent; experience with astronomical research; familiarity with scientific computing; expertise in data analysis; knowledge of IRAF, IDL or other software packages for astronomical data analysis; and programming ability. Additional mathematical, statistical, and computer skills are desirable. Candidates should have the ability to work with a minimum of direction, enjoy research and possess skills to develop excellent working relationships. Candidates should send a letter with current curriculum vitae and the names of three references to: Human Resources Manager Space Telescope Science Institute 3700 San Martin Dr. Baltimore, MD 21218 Women and minorities are strongly urged to apply. AAE/EOE. ================================================================================ RECENT PREPRINTS ---------------- We draw your attention to these papers, based on FOS 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. BOHLIN, R.C. "Spectrophotometric standards from the far-UV to the near-IR on the white dwarf flux scale" AJ accepted BOWEN, D.V.; BLADES, J.C.; PETTINI, M. "Extended Ly alpha absorbing halos around nearby galaxies?" ApJ accepted VASSILIADIS, E.; DOPITA, M.A.; BOHLIN, R.C.; HARRINGTON, J.P.; FORD, H.C.; MEATHERINGHAM, S.J.; WOOD, P.R.; STECHER, T.P.; MARAN, S.P. "Hubble Space Telescope observations of planetary nebulae in the Magellanic clouds. III. Ultraviolet spectroscopy using the Faint Object Spectrograph" ApJS accepted KORMENDY, J.; BENDER, R.; RICHSTONE, D.; AJHAR, E.A.; DRESSLER, A.; FABER, S.M.; GEBHARDT, K.; GRILLMAIR, C.; LAUER, T.R.; TREMAINE, S. "Hubble Space Telescope spectroscopic evidence for a 2 x 10 (9)-M black hole in NGC 3115" ApJ 3-10-95 HALPERN, J.P.;ERACLEOUS, M.; FILIPPENKO, A.V.; CHEN, K. "Hubble Space Telescope ultraviolet spectrum of Arp 102B, the prototypical double-peaked emission-line AGN" ApJ 6-20-96 SCUDERI, S.; PANAGIA, N.; GILMOZZI, R.; CHALLIS, P.M.; KIRSHNER, R.P. "Properties of star 2, one of the SN 1987A companions, derived from HST-FOS observations" ApJ accepted HALPERN, J.P.;ERACLEOUS, M.; FILIPPENKO, A.V.; CHEN, K. "Hubble Space Telescope ultraviolet spectrum of Arp 102B, the prototypical double-peaked emission-line AGN" ApJ 6-20-96 BOWER, G.A.; WILSON, A.S.; HECKMAN, T.M.; RICHSTONE, D.O. "Double-peaked broad emission lines in the nucleus of M81" AJ accepted DOPITA, M.A.; ALLEN, M.; BICKNELL, G.V.; SUTHERLAND, R.S.; KORATKAR, A.; EVANS, I.; HAWLEY, J.F.; SADLER, E. "Shock excitation of LINERs" Phys. of LINERs ROSEN, S.R.; PRINJA, R.K.; DREW, J.E.; MASON, K.O.; HOWELL, S.B. "HST UV observations of the disk and wind of V795 Her" Keele CV ROSEN, S.R.; PRINJA, R.K.; HOWELL, S.B.; DREW, J.E.; MASON, K.O. "Untangling the UV disk and wind emission in V795 Her via HST observations" STAVROYIANNOPOULOS, D.; ROSEN, S.R.; WATSON, M.G.; HOWELL, S.B. "Spin and beat phenomena in time-resolved HST UV spectroscopy of PQ Gem" MNRAS ================================================================================ APPENDIX: FOS contacts ----------------------- Any questions about the scheduling of your observations should be addressed to your Program coordinator. Any Technical proposal preparation and Post-Observation questions can be addressed to your Contact Scientist. If you do not know who these persons are, you can find the information at http://www.stsci.edu/public/propinfo.html. 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 fos_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. ================================================================================