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Last modified: 4 November 2010


Header Keywords

The CALDB is modeled after the HEASARC CALDB and is assembled based on the mandatory calibration file keywords prescribed by that group. At the end of Chandra's lifetime, the CALDB will be ingested into the HEASARC CALDB structure, where all the calibration databases for previous HEASARC missions are maintained.

The FITS header keyword structure specifies the subdirectory into which each file is to be placed, and provides the indexing information by which to select the file for use in processing and analysis. It is the function of the header specification and index to provide a unique specification for each and every active file, so that only one file and extension are returned for a sufficient indexing specification.

Conventions have been established for Chandra header keywords used by the CALDB; they are outlined in the ASC FITS Designer's Guide (PS, 40pp). Further details are also available from the CALDB Header Specifications reference document.

Keyword Specifications

The list of required keywords for Chandra CALDB files is given in Table 1. The keywords with a "Y" in the Index column are identical to those in the HEASARC list and are included in the index files.

Table 1: Mandatory keywords for Chandra CALDB files.



Allowed Values



TELESCOP Y CHANDRA Name of the satellite 1
DETNAM Y ACIS-n (n=0,9), HRC-S, HRC-I, ACA-P, ACA-R, NONE; nonessential Detector subelement names  
FILTER Y NONE, HESF, LESF, UVIS-I, UVIS-S; nonessential Items allowed as filter values, usually NONE  
GRATING N NONE, LETG, HETG Transmission grating assembly 2
GRATTYPE N HEG, MEG, LEG; nonessential Transmission grating sub-element 3
CDTP0001 Y DATA, TASK, FEF Real calibration data, virtual data, or FEF  
CCLS0001 Y BCF, CPF Basic calibration file or calibration product file  
CCNM0001 Y See Table 2 Contents descriptor.  
CVSD0001 Y yyyy-mm-ddThh:mm:ss Observation date after which data may be used  
CVST0001 Y hh:mm:ss Redundant; used by indexing routine. It must agree with CVSD0001  
CDES0001 Y (various possible values) Descriptive summary of calibration dataset  
CBDn0001 Y (various possible values) Parameter limits for a given dataset 2, 3

Notes for Table 1:

  1. By convention, the TELESCOP keyword must be set to CHANDRA, although the conventions allow AXAF as well. It was necessary to choose one value for use in the CALDB.

  2. When not set to NONE, the GRATING keyword is carried to the index using a CBDn0001 keyword such as CBD30001 = 'GRATING(HETG)'. This is done so that the value may be selected for an index search.

  3. The GRATTYPE keyword allows distinction between HEG and MEG. It is indexed with a CBD keyword as well, such as CBD40001 = 'GRATTYPE(MEG)'.

The process of implementing the CALDB involved coordinating Chandra FITS keyword standards with the indexing requirements of the Chandra CALDB within the guidelines provided by the HEASARC. Additions to the HEASARC standards were necessary, most commonly in the area of calibration file types, as many more exist for Chandra than for any previous mission. A number of new CALDB keyword values specific to Chandra were invented; these may be used by future missions with similar calibration requirements.


The codename (CCNM0001 keyword) value indicates the type of calibration data that is stored in the FITS file; Table 2 lists the allowed values.

Table 2: Codename values currently active in the Chandra CALDB.



Calibration Class




Descriptive Summary

ACIS, HRC BCF BADPIX Detector bad pixel list
ACIS BCF CONTAM ACIS filter contamination coefficients
ACIS BCF GRADE Detector grade table
ACIS BCF DET_GAIN Detector gain table
ACIS BCF EVTSPLT Event and split thresholds
ACIS, HRC BCF QE, QEU Mean, uniformity quantum efficiency tables
ACIS, HRC BCF GTI_LIM Parameter limits for GTI
ACIS, HRC CPF SPECRESP Spectral response
ACIS, HRC CPF MATRIX Redistribution and spectral response matrix
ACIS CPF OSIP Order-sorting table
ACIS, HRC CPF RPSF Radial point spread functions
ACIS, HRC CPF 2D_PSF Two-dimensional point spread functions
ACIS CPF FEF_PI FEF for RMFs with mkrmf
ACIS CPF FEF_PHA FEF for RMFs with mkrmf
HRC BCF GMAP Detector gain correction map
HRC BCF DEGAP Degap correction table
HRC BCF EFTEST Event flatness test coefficient table
HRC BCF FPTEST Event hyperbolic test coeffcient table
HRC BCF SATTEST Event amp saturation test coefficient table
HRC BCF TAPRINGTEST Event tap-ringing test coefficient table
TEL BCF AIMPTS Detector aimpoint positions
TEL BCF GEOM Detector geometry
TEL BCF SKY Detector sky coordinate system
TEL BCF TDET Tiled detector coordinate system
TEL BCF OBI_TOL Observation interval tolerances
TEL/HRMA BCF AXEFFA Axial effective area
TEL/HRMA BCF EFFAREA Off-axis effective area
TEL/HRMA BCF VIGNET Vignetting function
TEL/HRMA CPF RPSF Radial point spread function
TEL/HETG BCF GREFF Grating efficiency
TEL/HETG CPF FEF FEF for grating RMFs with mkrmf
TEL/HETG CPF SPECRESP Grating spectral response
TEL/HETG CPF MATRIX Grating redistribution matrix
TEL/LETG BCF GREFF Grating efficiency
TEL/LETG CPF FEF FEF for grating RMFs with mkrmf
TEL/LETG CPF SPECRESP Grating spectral response
TEL/LETG CPF MATRIX Grating redistribution matrix
PCAD BCF GYRO_SFMA Gyro scale factor misalignment matrix
PCAD BCF IRU_CHAR PCAD IRU characteristics
PCAD BCF RWA_BSPD Bad reaction wheel speeds
PCAD BCF ALIGN Alignment matrix
PCAD BCF FID_POS Fid light positions
PCAD BCF CCD_CHAR CCD characteristics
PCAD BCF CTI ACA charge transfer inefficiency
PCAD BCF FDC ACA field distortion coefficients
PCAD BCF CCD_RESP CCD response image
PCAD BCF DARK_CURR CCD dark current image
SIM BCF DET_POS Default SIM positions
SIM BCF DET_POSCORR Default SIM position corrections
EPHIN BCF GEOM Geometric factors