*******************************THIS FILE IS MORE THAN 80 CHARACTERS WIDE!************************************* FOS Dead Diode Reference Files: A Quick Reference Guide to the Appropriate File for a Particular Date and Instrumental Configuration Cynthia J. Taylor Space Telescope Science Institute August 1994 Abstract Complete tabulations of recommended Dead Diode reference files (.r4h, .r4d) for each specified USEAFTER date are presented in a convenient matrix format AS OF 6 AUGUST 1994. List of all Dead Diode reference files delivered to Calibration Data Base System (CDBS) will be in CAL/FOS-113. ASCII text and Postscript versions of the tables and explanatory test in this report will be maintained on STEIS and will be available for anonymous ftp from stsci.edu. Both the STEIS tables and explanatory text will be updated periodically. I. Introduction Each pixel in an FOS spectrum contains contributions from several neighboring diodes. A diode will contribute to a fixed number (NXSTEPS X OVERSCAN) of pixels (usually 20). Therefore when a diode dies or becomes noisy, there is an "absorption line" (for dead diodes) or an "emission line" (for noisy diodes) that is NXSTEPS X OVERSCAN pixels wide. Once a diode is identified as dead or too noisy (see Section III), it must be disabled onboard the spacecraft. The disabling is done via the commanding instruction, lydif_chnl, and is made at the start of a Science Mission Schedule (SMS). CALFOS corrects for the disabled diodes as part of the conversion to count rates step (see HST Data Handbook, "Conversion to Count Rates", page 269 for more detail). The list of disabled diodes is taken either from the appropriate dead diode reference file or from the unique data log (.ulh) depending on the value of the science header keyword, DEFDDTTBL. If the value of DEFDDTTBL value is TRUE then the list of disabled diodes is taken from the unique data log. If DEFDDTTBL is FALSE, then the disabled diode list is from the dead diode reference file. Since April 1992 the default value for DEFDDTTBL has been FALSE. If a given pixel has one (or more) disabled or dead diodes contributing to its value then CALFOS corrects the pixel value by the following equation: corr = obs (total / (total-dead)) where corr is the corrected pixel value, obs is the observed pixel value, total is the total number (live + dead) diodes contributing to the pixel, and dead is the number of dead diodes contributing to the pixel (HST Data Handbook, page 269). OVERSCAN number of diodes contribute to a given pixel value. II. Description of the Tables It is very important to use the correct reference file for the appropriate date and detector. Tables 1 and 2 show the recommended Dead Diode reference files for each detector and observation date. The first column is the Dead Diode reference HEADER file (the corresponding Dead Diode reference DATA file, .r4d, is not listed in the table). The "Begin Date" is the USEAFTER date associated with each file and is the earliest date a file should be used. The "End Date" is the last date a file should be used. The last column shows the diodes disabled on the scale of 0-511 (IRAF/STSDAS is on the 1-512 scale - see below for explanation). Note that in Table 2, files das1303py.r4h and d9h1244ay.r4h have the exact same diodes disabled. This is because they are copies of the same file. A mistake in the USEAFTER date was made during delivery. Either file will be correct to use for Blueside data taken after September 7, 1993. A complete history of all the delivered Dead Diodes reference files will be covered in CAL/FOS-113. Tables 3.1 and 3.2 show the list of: disabled dead, disabled cross-wired (in Table 3.1), disabled doisy, enabled but possibly noisy, and enabled but intermittently dead (in Table 3.2). The diodes listed are on the 0-511 scale. The Research Support Branch Analysis Hot Line should have the current version of these tables, since this report will be updated only when there is a new Dead Diode reference file. III. Identification of Diodes New dead or noisy diodes can easily be identified by comparing the raw data file (.d0h) to the calibrated file (.c1h or .c4h). The raw data file will have several sharp edged absorption features (that are exactly NXSTEPS X OVERSCAN pixels wide) that are due to disabled diodes . If there is an absorption feature in the same pixel range in the calibrated file as in the raw data file and you have verified you are using the appropriate Dead Diode file for the observation date, then the feature is a new dead diode. If there is a sharp edged emission feature in both the raw and the calibrated data then it's a noisy diode. If the emission line is just in the calibrated data, then you used an incorrect Dead Diode reference file. To identify the diode that is noisy/dead, you must determine the range of pixels that are affected. The easiest method is to plot the region around the affected pixels. {If you are using the IRAF/STSDAS task sgraph, please use caution in your pixel range since IRAF assigns "1" to the first pixel of the range (i.e. if you plot pixels 155 - 206, pixel 155 will be assigned "1"). It is a good idea to start the pixel range on a "1".} Determine the first pixel that is affected. The diode affected (on 0-511 scale) is: (for IRAF) DIODE = (pixel-1) / NXSTEPS (for IDL) DIODE = pixel / NXSTEPS where pixel is the first pixel affected. You have to subtract one from the pixel number in IRAF because IRAF pixel range is from 1 to 2064 (for NXSTEPS = 4 and OVERSCAN = 5) while IDL pixel range is from 0 to 2063. The diode range convention is based on IDL, hence the range 0-511. However IRAF uses the 1-512 numbering convention. Thus if you listpix the Dead Diode reference file or have data with NXSTEPS = 1 and OVERSCAN = 1, you will have to subtract one from the pixel number (which is the same as the diode number) to get the "proper" diode number. If you have discovered a new dead or noisy diode, please contact Research Support Branch Analysis Hot Line (telephone: (410) 338-1082 or e-mail: analysis@stsci.edu). For dead diodes, usually a new Dead Diode reference file will be made available so you can recalibrate your data. Announcements of new Dead Diode reference files will be posted on STEIS. If you don't want to recalibrate your data, you can use the IRAF task fixpix and the equation on page 1 to manually correct the affected pixels. If you have a noisy diode, unfortunately you can't remove the noisy diode effect by recalibrating the data. You can use IRAF tasks fixpix or splot (in the etch-a sketch mode) to smooth over or blank out the affected pixels (HST Data Handbook, "Effect of Noisy Diode", page 236). In the future, there will be an STSDAS task that will correct for dead and noisy diodes or for an incorrect Dead Diode reference file without having to recalibrate the data. The test version is currently only available at STScI in the stlocal.testfos package as the task fixdiodes. IV. Availability of this Information and Updates Periodically updated ASCII text and Postscript versions of Tables 1, 2, 3.1, and 3.2 will be maintained in the /instrument_news/fos directory on STEIS and will be available for anonymous ftp from stsci.edu. The files will be named "dead_diode_tables_mmmyy.ps" and "dead_diode_tables_mmmyy.txt", where the extension "ps" indicates the Postscript version, the extension "txt" denotes the ASCII version, and "mmmyy" is the posting date in month and year. For example, the first files posted are "dead_diode_tables_aug94.ps" and "dead_diode_tables_aug94.txt". There will also be announcements posted for new dead diodes (since data may have to be recalibrated) in the same /instrument_news/fos directory. You can also use the STSDAS task getreffile to list the recommended reference files and tables for a particular observation. The Calibration Reference screens in StarView will also list the recommended reference files for an observation dataset (see HST Data Handbook, "Identifying the Best Files Using StarView", page 71). If you are still unsure you are using the correct Dead Diode reference file, please contact Research Support Branch Analysis Hot Line (telephone: (410) 338-1082 or e-mail: analysis@stsci.edu). References Cohen, R.D. and Beaver, E.A., 1990, Instrument Science Report CAL/FOS-050. Cohen, R.D., Tudhope, D.S., and Beaver, E.A., 1989, Instrument Science Report CAL/FOS-051. Cohen, R.D., 1992, Instrument Science Report CAL/FOS-074. Koratkar, A.P., 1994, "HST Data Handbook (ed. S. Baum)". Taylor, C.J and Kinney, A.L., 1994, CAL/FOS-100. Taylor, C.J. and Keyes, C.D., 1994, Instrument Science Report CAL/FOS-113. Table 1: AMBER DEAD DIODE REFERENCE FILES Begin Date Filename (USEAFTER) End Date Diodes Disabled on 0-511 scale -------- ---------- -------- ------------------------------ c5s1508ay.r4h 24 Apr 90 26 Aug 90 2,6,212,235,261,285,344,381,405,409,486 c5s15086y.r4h 27 Aug 90 13 Sep 90 2,6,212,285,405,409,486 c5s15083y.r4h 14 Sep 90 14 Dec 90 2,6,110,212,285,405,409,486 c5s15084y.r4h 15 Dec 90 26 Oct 91 2,6,110,197,212,285,405,409,486 c5s15088y.r4h 27 Oct 91 13 Dec 91 2,6,29,110,197,212,285,405,409,486 c5s15080y.r4h 14 Dec 91 02 Aug 92 2,6,29,110,189,197,212,285,405,409,486 c861559ay.r4h 03 Aug 92 10 Oct 93 2,6,29,110,189,197,212,285,380,405,409,486 da80843ny.r4h 11 Oct 93 11 Oct 93 2,6,29,110,189,197,212,285,380,381,405,409,412,486 dap1024ay.r4h 12 Oct 93 2,6,29,110,189,197,212,285,308,380,381,405,409,412,486 Table 2: BLUE DEAD DIODE REFERENCE FILES Begin Date Filename (USEAFTER) End Date Diodes Disabled on 0-511 scale -------- ---------- -------- ------------------------------ c6q16023y.r4h 24 April 90 17 May 90 47,49,55,73,201,218,219,223,268,284,409,415,427,451,465,472 c6q1601jy.r4h 18 May 90 10 Jun 90 47,49,55,73,201,218,219,223,225,268,284,409,415,427,451,465,472 c6q1601gy.r4h 11 Jun 90 31 Oct 90 47,49,55,73,201,218,219,223,268,284,409,415,427,451,465,472 c6q1601dy.r4h 01 Nov 90 19 Feb 91 31,47,49,55,73,201,218,219,223,225,235,241,268,284,409,415,427,451,465,472,497 c6q1601ny.r4h 20 Feb 91 31 May 91 31,47,49,55,73,201,218,223,225,235,241,268,284,398,409,451,465,472,497 c6q16019y.r4h 01 Jun 91 19 Jun 91 31,47,49,55,73,201,218,223,225,235,241,268,284,398,409,451,465,471,472,497 c6q1601ry.r4h 20 Jun 91 27 Aug 91 31,47,49,55,73,201,218,223,225,235,241,268,284,398,409,441,451,465,471,472,497 c6q16020y.r4h 28 Aug 91 12 Apr 92 31,47,49,55,73,101,201,218,223,225,235,241,268,284,398,409,441,451,465,471,472,497 c6p1432my.r4h 13 Apr 92 14 Feb 93 31,47,49,55,73,101,201,218,223,225,235,241,268,284,398,409,427,441,451,465,471,472,497 d2a16223y.r4h 15 Feb 93 02 May 93 31,47,49,55,73,101,201,218,223,225,235,241,268,284,398,409,415,427,441,451,465,471,472,497 d4s1044fy.r4h 03 May 93 06 Sep 93 31,47,49,55,73,101,144,201,218,223,225,235,241,268,284,398,409,415,427,441,451,465,471,472,497 das1303py.r4h 07 Sep 93 16 Sep 93 31,47,49,55,73,101,144,201,218,223,225,235,241,268,284,292,398,409,415,427,441,451,465,471,472,497 d9h1244ay.r4h 17 Sep 93 31,47,49,55,73,101,144,201,218,223,225,235,241,268,284,292,398,409,415,427,441,451,465,471,472,497 FOS DEAD AND NOISY DIODE SUMMARY (updated: 6 Aug 94. DIODE RANGE IS 0-511) Table 3.1: BLUE DETECTOR DISABLED DISABLED DISABLED ENABLED Dead Diodes Noisy Diodes X-wired But Possibly Noisy ----------- ------------ ------- ------------------ 49 31 47 8 101 73 55 138 223 144 139 284 201 209/210 292 218 421 409 225 426 441 235 471 241 268 398 415 427 451 465 472 497 -------------------------------------------------------------------- 8 16 2 6 Total Blue Disabled: 26 Table 3.2: AMBER DETECTOR DISABLED DISABLED ENABLED ENABLED Dead Diodes Noisy Diodes But Possibly Noisy But Intermittent Dead ----------- ------------ ------------------ --------------------- 2 110 142 97 6 189 153 29 285 174 197 380 258/259 212 381 261 308 405 410 486 409 412 ------------------------------------------------------------------------------ 7 8 6 1 Total Amber Disabled: 15