STScI Logo

afiles astcat


NAME · USAGE · ASTROMETRY_FILES · SAMPLE_STANDARD_ASTROMETRY_FILE
SAMPLE_ASTROMETRY_FILE · SEE_ALSO

NAME

afiles -- describe the standard astrometry files

USAGE

help files

ASTROMETRY FILES

An astrometry file is any text file containing celestial coordinate information for a small region of the sky. A minimal astrometry file consists of a list of celestial coordinate pairs one pair per line. Most astrometry files also contain additional non- positional information, e.g. proper motions, magnitudes, colors, etc.

A standard astrometry file as an astrometry file containing a standard header describing the contents and format of the file. The astcat tasks use the header to decode the file. Normally the astrometry file header is derived from the parent astrometric catalog description in the catalog configuration file. If the astrometry file header is missing one may be constructed after the fact by setting the standard field description parameter in the acatpars parameter set and running the afiltcat task.

A set of standard field names is reserved for describing the format of astrometry files. The current list of standard field names is: id, ra, dec, era, edec, pmra, pmdec, epmra, epmdec, catsystem, equinox, epoch, px, rv, epx, erv, mag, color, emag, ecolor, xp, yp, xc, yc, exc, eyc, imag, and eimag. For more information about these fields type "help acatpars".

SAMPLE STANDARD ASTROMETRY FILE

A sample astrometry file in standard format is shown below.

# BEGIN CATALOG HEADER
#    type stext
#    nheader 1
#        csystem J2000
#    nfields 4
#        ra 1 0 d hours %12.3h
#       dec 2 0 d degrees %12.2h
#      mag1 3 0 r INDEF %4.1f
#      mag2 4 0 r INDEF %4.1f
# END CATALOG HEADER

 00:00:01.443   -0:06:57.52  13.5  15.2
 00:00:01.574   -0:05:33.26  16.1  18.0
 00:00:01.904   -0:09:48.51  18.2  19.6
 00:00:02.529   -0:04:21.53  13.4  14.4
 00:00:04.154   -0:01:56.32  17.1  18.3
 00:00:04.438   -0:05:00.03  11.4  13.5
 00:00:04.697   -0:03:24.59  16.9  17.7
 00:00:05.989   -0:02:46.36  15.1  17.6
 00:00:07.118   -0:09:03.53  19.1  19.8
 00:00:07.260   -0:06:47.95  17.0  17.7
 00:00:07.314   -0:00:22.35  15.3  16.8
 00:00:07.818   -0:02:25.90  12.2  12.4

SAMPLE ASTROMETRY FILE

A sample headerless astrometry file is shown below where ra, dec, mag1 and mag2 are stored in columns 1 through 4 respectively.

 00:00:01.443   -0:06:57.52  13.5  15.2
 00:00:01.574   -0:05:33.26  16.1  18.0
 00:00:01.904   -0:09:48.51  18.2  19.6
 00:00:02.529   -0:04:21.53  13.4  14.4
 00:00:04.154   -0:01:56.32  17.1  18.3
 00:00:04.438   -0:05:00.03  11.4  13.5
 00:00:04.697   -0:03:24.59  16.9  17.7
 00:00:05.989   -0:02:46.36  15.1  17.6
 00:00:07.118   -0:09:03.53  19.1  19.8
 00:00:07.260   -0:06:47.95  17.0  17.7
 00:00:07.314   -0:00:22.35  15.3  16.8
 00:00:07.818   -0:02:25.90  12.2  12.4

This file can be converted to standard form with the afiltcat task as follows

cl> agetcat input output filter- ra="1 hours %12.3h" dec="2 degrees %12.2h" \
mag="1-2 INDEF %4.1f"

or by editing in a header of the form shown in the previous section. The lines

# BEGIN CATALOG HEADER
# END CATALOG HEADER

delimit the header. The header must contain the type, nheader, and nfields keyword value pairs and accurate descriptions of file the format.

SEE ALSO

help catalogs, agetcat, afiltcat, acatpars


Search Form · STSDAS