GSC - HST Guide Star Catalog, Version 1.2
The Guide Star Catalog Version, Version 1.2 contains an astrometric recalibration and other refinements compared to the previous version (1.1). The overall rms error of the GSC 1.2 is estimated to be better than 0.3 arcseconds. The reference material for the GSC 1.2 reduction is the "Positions and Proper Motions Catalogue":
PPM-North, Roeser S. and Bastian U., 1988, Cat. <I/146> PPM-South, Bastian U. and Roeser S., 1993, Cat. <I/193> PPM-Suppl, Roeser S., Bastian U. and Kuzmin A., 1994, Cat. <I/208>and the Astrographic Catalogue (AC) which was used to remove the mean systematics common to all the plates. Additional information on the reduction is available at http://gsss.stsci.edu/Catalogs/GSC/GSC1/gsc12/DESCRIPTION.HTM
Notice that the HEASARC has made no attempt to combine objects with multiple listings in the GSC 1.2 Catalog (due to their being present on more than the plate) into a single entry in this database, as the HEASARC had done for its database version of the GSC 1.1 Catalog.
The HEASARC recommends that Browse cone searches not exceed a radius of 30 arcminutes, since, as one will quickly discover, a radius of 30 arcminutes usually contains hundreds if not thousands of stars. To search a larger area, we recommend that users construct a mosaic of the results of a sequence of 30-arcminute searches using offset coordinates. Notice that the default cone search radius is 1 arcminute.
Finally, notice that the STScI states that GSC 1.2 should NOT be used for HST phase 2 coordinates, as GSC 1.2 has not been installed in the HST ground system.
The Guide Star Catalog Version 1.2: an astrometric recalibration and other refinements. Morrison J.E., Roeser S., McLean B., Bucciarelli B., Lasker B. <Astron. J., 121, 1752 (2001)> =2001AJ....121.1752M
The original version of this catalog, GSC 1.0, is described in a series of papers:
Lasker et al. (1990AJ.....99.2019L), Russell et al. (1990AJ.....99.2059R); and Jenkner et al. (1990AJ.....99.2082J)
The GSC identification of the object; this is made up of the GSC prefix, a plate number (5 digits) and a star number on the plate (5 digits), with the latter two fields separated by a dash, as recommended by the Dictionary of Nomenclature of Celestial Objects.
The Right Ascension of the object in the selected equinox. In the original STScI Catalog, this was given in equinox J2000 and at the epoch of the plate in decimal degrees, to a precision of 0.00001 degrees. The overall rms error of positions in the GSC 1.2 is estimated to be better than 0.3 arcsec.
The Declination of the object in the selected equinox. In the original STScI Catalog, this was given in equinox J2000 and at the epoch of the plate in decimal degrees, to a precision of 0.00001 degrees. The overall rms error of positions in the GSC 1.2 is estimated to be better than 0.3 arcsec.
The esimated mean error in the position, in arseconds (").
The (usually photographic) magnitude for the object, in the band specified by the pmag_band parameter.
The mean error in the magnitude.
The band code for the magnitude designating the following combination of emulsion and filter:
pmag_band emulsion filter Notes --------- -------- -------- ----------------------- 0 IIIaJ GG395 SERC-J/EJ 1 IIaD W12 Pal Quick-V 3 --- B Johnson 4 --- V Johnson 5 IIIaF RG630 Red 6 IIaD GG495 Pal QV/AAO XV 7 103aO --- POSS-I Blue 8 103aE red plex POSS-I Red 10 IIaD GG495 GPO Astrograph 11 103aO GG400 Black Birch Astrograph 16 IIIaJ GG495 QV 18 IIIaJ GG385 POSS-II Blue
A stellar/non-stellar classification flag for the object, using the following definitions:
Code Meaning ---- ------- 0 Star 1 Galaxy 2 Blend 3 Non-Star 4 Unclassified 5 Artifact
An alphanumeric designation for the plate on which the object was found. This is referred to as the GSSS No. in the GSC documentation (cf. Lasker et al. 1990, AJ, 99, 2019, Table III), and is described as an "internal designation generated by the GSSS software system to provide a unique and operationally consistent plate name for catalog generation and storage."
A flag that is set to "T" if there are multiple entries at the same position in the GSC 1.2, and set to "F" otherwise.