PUBLIC RELEASE NOTES FOR THE CHANDRA CALDB I. CHANDRA CALDB VERSION: 1.1 Web page access to this information is under development. You will be notified of its location when it is ready. ACRONYMS & DEFINITIONS: PCAD Pointing Control and Aspect Determination CALALIGN PCAD alignment matrix, a calibration file applied in Aspect L1 pipeline which provides the data with which to correct sky coordinate positions. A. ITEM CHANGED: Time-dependent PCAD alignment (CALALIGN) files added. B. PROCESSING AFFECTED: ASPECT Level 1 Pipeline (ACIS-I and ACIS-S only) C. DATE OF THE CHANGE (TT): CALDB_DATE: 2000-04-25T04:00:00 Automatic Processing Date: 2000-04-30T11:45:00 Custom Processing Date: 2000-05-01T16:00:00 D. REASON FOR CHANGE: The Chandra CALDB has been updated to version 1.1 with the inclusion of twelve PCAD align files (CALALIGN), which correct for the long-term drift seen over August - November 1999 in ACIS-I and ACIS-S observations only. (HRC is not affected by this update!) Tom Aldcroft (ASPECT group) indicates that (for example) the sky coordinates for OBSID 376 had an offset of 1.9 arc seconds with the old CALALIGN file, but with the appropriate file from the new list the offset is now 0.4 arc seconds. We will have more information from a group of OBSID's shortly. This will be posted on the new web page for the Chandra CALDB. E: Detailed description of what has changed: This update was activated with ASCDSVER "R4CU5UPD3". Any processed files with ASCDSVER = R4CU5UPD3 or higher will employ the new PCAD align files until further notice. Please check your data files for the ASCDSVER variable to determine whether time-dependent PCAD alignments would have been applied to them or not. Using CIAO (UNIX): dmlist header | grep ASCDSVER Previous ASCDSVER's did not use the CALDB for ASPECT calibration file access. The above dates AP_DATE (automatic processing) and CP_DATE (custom processing) indicate the time in TT after which AP and CP began using R4CU5UPD3 to process for record. The new PCAD files are named, in chronological order of applicability (note the dates in the filenames): /data/CALDB/data/chandra/pcad/bcf/align/pcadD1999-07-19alignN0001.fits /data/CALDB/data/chandra/pcad/bcf/align/pcadD1999-07-29alignN0001.fits /data/CALDB/data/chandra/pcad/bcf/align/pcadD1999-08-08alignN0001.fits /data/CALDB/data/chandra/pcad/bcf/align/pcadD1999-08-18alignN0001.fits /data/CALDB/data/chandra/pcad/bcf/align/pcadD1999-08-28alignN0001.fits /data/CALDB/data/chandra/pcad/bcf/align/pcadD1999-09-07alignN0001.fits /data/CALDB/data/chandra/pcad/bcf/align/pcadD1999-09-17alignN0001.fits /data/CALDB/data/chandra/pcad/bcf/align/pcadD1999-09-27alignN0001.fits /data/CALDB/data/chandra/pcad/bcf/align/pcadD1999-10-07alignN0001.fits /data/CALDB/data/chandra/pcad/bcf/align/pcadD1999-10-17alignN0001.fits /data/CALDB/data/chandra/pcad/bcf/align/pcadD1999-10-27alignN0001.fits /data/CALDB/data/chandra/pcad/bcf/align/pcadD1999-11-06alignN0001.fits These file replace the previous single CALALIGN file, /data/CALDB/data/chandra/pcad/bcf/align/pcadD1999-08-12alignN0006.fits which includes only the corrections relevant for the beginning of Phase II of OAC (after the SSD was opened.) ************************************************************************** II. TECHNICAL INFORMATION ON NEW CALIBRATION DATA: From Dr. Tom Aldcroft (SOT/Aspect) 23 Mar 2000: [Referring to the pcad*.fits files above] "In each case the date corresponds to the valid start date for the file. I've set the DATE, TSTART, TSTOP, CVSD0001, and CVST0001 keywords, as well as some HISTORY records that describe the modifications. "The alignments for ACIS-S and ACIS-I at each epoch have been shifted (from the 20-Jan-00 align) as follows. HRC alignments are unchanged. "Before day 1999:310 -- Linear fit to ACIS-S shift data (from Maxim) "After day 310 -- Mean of ACIS-S shift "Here are the actual values, from the IDL code: ; Time dependent alignment shift: ; dy = ry1[0] + (doy-doy0) * ry1[1] For doy <= 310 (doy = day of year) ; dy = dy2 For doy > 310 ; ... and similarly for dz day0 = 228.0 ; Initial Day of Year in ACIS-S data ry1 = [0.322972, 0.0184397] ; Linearly increasing offset before 1999:310 rz1 = [0.0984789, 0.0116385] dy2 = 1.76760 ; Constant offset after 1999:310 dz2 = 1.12112 " Therefore a linear correction versus time is made over Launch date through 1999:310. A constant offset is employed thereafter to correct sky coordinates. - Dale E Graessle -- Chandra CALDB Manager