I. Introduction

CalDB 3.4.4 was required because of a programmatic action to switch off the ACIS detector housing heater (DHH) assembly, which was done in April of 2008. This action has allowed ACIS to operate at a more consistent focal plane temperature (FP_TEMP) near the specified -120C. The resulting alignment drift between the ACIS and the ACA requires an extra parametrization of their co-alignment to maintain astrometric standards for Chandra.

II. Summary of Changes

PCAD ALIGN/FID_POS/FID_COR (CALALIGN) files N0007

LOCATION: $CALDB/data/chandra/pcad/bcf/align/
FILENAMES:
pcadD1999-07-19alignN0007.fits
pcadD1999-07-29alignN0007.fits
pcadD1999-08-08alignN0007.fits
pcadD1999-08-18alignN0007.fits
pcadD1999-08-28alignN0007.fits
pcadD1999-09-07alignN0007.fits
pcadD1999-09-17alignN0007.fits
pcadD1999-09-27alignN0007.fits
pcadD1999-10-07alignN0007.fits
pcadD1999-10-17alignN0007.fits
pcadD1999-10-27alignN0007.fits
pcadD1999-11-06alignN0007.fits
pcadD1999-12-01alignN0007.fits
pcadD2000-01-01alignN0007.fits
pcadD2000-02-01alignN0007.fits
pcadD2000-03-01alignN0007.fits
pcadD2000-04-01alignN0007.fits
pcadD2000-05-01alignN0007.fits
pcadD2000-06-01alignN0007.fits
pcadD2000-07-01alignN0007.fits
pcadD2000-08-01alignN0007.fits
pcadD2000-09-01alignN0007.fits
pcadD2000-10-01alignN0007.fits
pcadD2000-11-01alignN0007.fits
pcadD2000-12-01alignN0007.fits
pcadD2001-01-01alignN0007.fits
pcadD2001-02-01alignN0007.fits
pcadD2001-03-01alignN0007.fits
pcadD2001-04-01alignN0007.fits
pcadD2001-05-01alignN0007.fits
pcadD2001-06-01alignN0007.fits
pcadD2001-07-01alignN0007.fits
pcadD2001-08-01alignN0007.fits
pcadD2001-09-01alignN0007.fits
pcadD2001-10-01alignN0007.fits
pcadD2001-11-01alignN0007.fits
pcadD2001-12-01alignN0007.fits
pcadD2002-01-01alignN0007.fits
pcadD2002-02-01alignN0007.fits
pcadD2002-03-01alignN0007.fits
pcadD2002-04-01alignN0007.fits
pcadD2002-05-01alignN0007.fits
pcadD2002-06-01alignN0007.fits
pcadD2002-07-01alignN0007.fits
pcadD2002-08-01alignN0007.fits
pcadD2002-09-01alignN0007.fits
pcadD2002-10-01alignN0007.fits
pcadD2002-11-01alignN0007.fits
pcadD2002-12-01alignN0007.fits
pcadD2003-06-09alignN0007.fits
pcadD2006-12-10alignN0007.fits

PIPES/TOOLS affected: Aspect L1 pipeline only

ECR: https://icxc.harvard.edu/calco/ard_updates/ECR/Approved_ECRs/ECR_2008_009.html

III. Technical Details

The shut-off of the ACIS DHH planned for early April 2008 will require new alignment parameters to be introduced in Aspect L1 processing. To that end, a single (identical) BINTABLE extension (HDUNAME=) "ACISFIDCORR" has been added to each PCAD alignment file above. The newly-enhanced Aspect L1 software will use this information to calculate the astrometry of ACIS observations.

For technical details, the user is referred to the ASPECT Calibration Page at http://asc.harvard.edu/mta/ASPECT/ECR_acisfidcorr/.