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The HST Guide Star Catalog
I/220            The HST Guide Star Catalog            (Lasker+ 1992)
================================================================================
The Guide Star Catalog Version 1.1 - An all-sky astrometric and photometric
   catalog to support the operation of the Hubble Space Telescope
   
The Guide Star Catalog Version 1.0 is described in a series of papers:
I.   Astronomical foundations and image processing
     Lasker B.M., Sturch C.R., McLean B.J., Russell J.L., Jenkner H., Shara M.M.
     
     =1990AJ.....99.2019L
II.  Photometric and astrometric models and solutions
     Russell J.L., Lasker B.M., McLean B.J., Sturch C.R., Jenkner H.
     
     =1990AJ.....99.2059R
III. Production, database organization, and population statistics
     Jenkner H., Lasker B.M., Sturch C.R., McLean B.J., Shara M.M., Russell J.L.
     
     =1990AJ.....99.2082J
================================================================================
ADC_Keywords: Surveys ; Positional data

Abstract:
   The Guide Star Catalog (GSC), which has been constructed to support the
   operational need of the Hubble Space Telescope contains nearly 19
   million objects brighter than sixteenth magnitude, of which more than 15
   million are classified as stars. This catalog provides positions and
   magnitudes for these stars.

Introduction:
   The original version of this catalog, GSC 1.0, is described in a series
   of papers: Lasker et al. (1990); Russell et al. (1990); and Jenkner et
   al. (1990); hereafter referred to as Papers I, II, and III. Additions
   and corrections made in GSC 1.1 address:
      incompleteness, misnomers, artifacts, and other errors due to the
         overexposure of the brighter stars on the Schmidt plates,
      the identification of blends likely to have been incorrectly
         resolved,
      the incorporation of errata reported by the user-community or
         identified by the analysis of HST operational problems.

   Among the primary authors of the GSC 1.0 and the associated systems, the
   scientific responsibilities were divided as follows: Helmut Jenkner,
   system coordination and overall design; Barry M. Lasker, astrophysics
   and photometry; Brian J. McLean, algorithmic analysis and systems
   development; Jane L. Russell, astrometry; Michael M. Shara, system
   management; and Conrad R. Sturch , production management and quality
   control. GSC 1.1 analysis and production were performed primarily by
   Jesse B. Doggett, Daniel Egret, Brian J. McLean, and Conrad R. Sturch.

   Helmut Jenkner is on assignment from the European Space Agency; Jane L.
   Russell is currently affiliated with the Applied Research Corporation,
   Landover, MD; and Conrad R. Sturch is with the Astronomy Programs,
   Computer Sciences Corporation at Space Telescope Science Institute.
   Daniel Egret is affiliated with Observatoire de Strasbourg, France.

Astronomical and Algorithmic Foundation:
   As described in Paper I, the GSC is primarily based on an all-sky,
   single epoch, single passband collection of Schmidt plates. For centers
   at +6 degree s and north, a 1982 epoch "Quick V" survey was obtained by
   the Palomar Observatory, while for southern fields, materials from the
   UK SERC J survey (epoch approximately 1975) and its equatorial extension
   (epoch approximately 1982) were used. In addition, over 100 short-
   exposure plates were taken with the Palomar Oschin and UK Schmidt
   telescopes to cover complex regions including the southern Milky Way,
   the Magellanic Clouds, and M31. These northern, southern, and
   supplemental plates hereafter are referred to as N, S, and X plates,
   respectively. The plates were digitized into 14000-square rasters at 25
   um sample intervals using modified PDS microdensitometers.

   The sky-background was modeled with a bi-dimensional cubic spline
   approximation to the modal level. Then an object finder, based on
   locating connected pixels at a certain threshold above the background,
   was used to obtain, for each plate, a list of positions, sizes,
   intensities, and related descriptive parameters. Images with multiple
   peaks were deblended by an algorithm based on correlations against a
   library of stellar images.

   The identified objects were classified as stars or non-stars by an
   interactive multivariate Bayesian classifier that used image features
   from the object-detection steps and was started from a small set of
   objects visually identified on each plate. Comparison of classifications
   from multiply catalogued objects in the plate overlap areas shows that
   the purity of objects classified as stars is typically 97 percent.

Photometric and Astrometric Calibrations:
   The GSC calibrations were obtained on a plate-by-plate basis by
   polynomial modeling against the photometric and astrometric reference
   catalogs.

   Photometry is available in the natural systems defined by the individual
   plates in the GSC collection (generally J or V), and the calibrations
   are done using B, V standards from the Guide Star Photometric Catalog
   (Lasker, Sturch, et al. 1988).

   In Paper II the overall quality of the photometry near the standard
   stars was estimated from the fits and other tests to be 0.15 mag (one
   sigma, averaged over all plates), while the quality far from the
   sequences was estimated from the all-sky plate-to-plate agreement and
   from comparisons with independent photometric surveys to be about 0.3
   mag (one sigma), with about 10% of the errors being greater than 0.5
   mag. Additionally, Ratnatunga's (1990) comparison of the GSC against
   totally independent J-band photographic photometry for three southern
   fields (20 sq deg area) for 12.5 < J < 15.5 shows agreement at the
   0.1-0.2 mag level.

   Astrometry, at equinox J2000, is available at the epochs of the
   individual plates used in the GSC; and the reductions to the reference
   catalogs (AGK3, SAOC, or CPC, depending on the declination zone) use
   third order expansions of the modeled plate and telescope effects. The
   fits to the reference catalogs lie in the range 0.5" to 0.9", and most
   of this is attributable to errors in the reference catalogs, to
   centroiding errors on the relatively large images of the reference
   stars, and to unmodeled astrometric effects.

   Paper II reported estimates of the overall external astrometric error,
   produced by comparisons of independently measured positions, in the
   range 0.2" to 0.8" (per coordinate), depending on the areas of the plate
   and the sky. Then from a more extensive analysis against the Carlsberg
   Automatic Meridian Circle data, Taff et al. (1990) found that GSC
   absolute positional errors from plate center to edge vary from 0.5" to
   1.1" in the north and from 1.0" to 1.6" in the south, and that relative
   errors at half-degree separations range from 0.33" to 0.76" depending
   upon hemisphere and magnitude.

Production, Database, Organization, and Population Statistics:
   Paper III describes the software system used to produce the GSC. It
   consisted of a set of (primarily non-interactive) image-processing and
   calibration programs interconnected by a set of pipeline files and
   supported by databases organized on a plate-by-plate basis. A set of
   utility programs was also provided to support quality control and to
   correct operational problems.

   Object names are of the form GSC rrrrr nnnnn, where the first field
   specifies an internal region number and the second is an ordinal within
   it. For objects catalogued from more than one photographic plate, an
   entry was made from each image; and all entries for the same object were
   given the same unique name.

   Paper III also reviews the database for compiling statistics of objects
   with multiple entries and the details of the organization and structure
   of the GSC, including the provisions for assigning unique names, for
   cataloguing objects lying in the plate overlap regions, for rapidly
   indexing positions against regions, and for recovering the original
   plate measurements. The separate count statistics for stellar and
   non-stellar objects on a plate-by-plate basis are provided in the
   supporting tables.

 User Interfaces, Utilities, and Astronomical Applications:
   The all-sky collection of Schmidt plates that were digitized, archived
   to optical disc, and processed to generate the Guide Star Catalog (GSC)
   constitute a general image resource for astronomical research.

   This data set, combined with the computing environment provided by the
   Guide Star Astrometric Support Package (GASP), major elements of which
   are exported within the Space Telescope Science Data Analysis System,
   provides random access to a digital image in any part of the sky. The
   GASP environment also supports access to the GSC and to other major
   astronomical catalogs. The GASP is part of the STScI SDAS package which,
   together with IRAF, can be obtained through the STScI World Wide Web
   pages.

Revisions in GSC 1.1:
   The GSC 1.1 activities performed to address a number of known problems
   in GSC 1.0 are summarized here and described in detail in the text file
   for this revision, rev_1_1.tbl.

   Two concerns related to the brighter stars arise from the heavily
   overexposed images on the Schmidt plates used in the GSC, namely an
   incompleteness and a reduced precision. Both are addressed in the domain
   V < 7.5 by the use of data from the INCA Data Base (Turon et al. 1992;
   Jahreiss et al. 1992; Grenon et al. 1992) in the Tycho Input Catalog
   (TIC; Egret et al. 1992). Such entries are designated by the plate
   identifier +056 in GSC 1.1. The limit of V < 7.5 preserves the original
   GSC data for objects that were used in the GSC 1.0 astrometric
   calibration.

   Naming errors occur when objects catalogued from more than one
   photographic plate have positional errors sufficiently large that
   cross-matching of the overlapping plate areas is done incorrectly. The
   most significant known instances of this in GSC 1.0 were associated with
   overexposed (and therefore badly centroided) images of the brighter
   stars. A search around the positions of the INCA stars facilitated the
   identification of these naming errors, which were then removed in GSC
   1.1.

   GSC 1.0 contains many pairs of objects (from single plates) with
   separations significantly smaller than the expected resolution of the
   catalog, which Garnavich (1991), based on a study of four northern
   plates, estimates at ~ 10" for 8.0 < V < 14.0. Visual inspection shows
   that these are generally blends that have been properly resolved, but
   then affected by a centroider defect that made the separations
   artificially small. Such components of blends with incorrect separations
   are given a classification of 2 (blend; cf. the text file for a full
   listing of the codes).

   For stars with V < 8, image-processing artifacts near the diffraction
   spikes exist in GSC 1.0. In GSC 1.1, potential artifacts were identified
   by use of a purely geometrical criterion (proximity of the object to the
   spike), and were assigned a classification of 5.

   Small areas around southern stars brighter than V ~ 3 are not processed
   from the Schmidt plates and were left blank in GSC 1.0. For these, GSC
   1.1 contains entries from supplemental astrograph plates taken with the
   Gran Prisma Objectif (GPO) telescope on La Silla, and the astrograph at
   the Black Birch Observatory (BBO) in Blenheim, New Zealand. Because of
   their smaller fields, the photometric and astrometric calibrations of
   data from most GPO and a few BBO plates were performed against nearby
   GSC entries based on the Schmidt plates.  The details for these plates
   are given in the file bright.plt.

   A number of specific errors in GSC 1.0 have been identified by the
   user-community and by analyses of HST operational problems. These
   generally involve naming errors, plate flaws, misclassifications, and
   multiple stars; most are individually corrected in GSC 1.1. Also, the
   photometric error parameter in GSC 1.1 is now correctly described by
   equation (3) in Paper II; i.e., the erratum of footnote 5 therein is no
   longer pertinent.

Organization of the data files:
   The Guide Star Catalog is subdivided into regions that are bounded by
   small circles of right ascension and great circles of declination, and
   that are numbered consecutively from 0001 to 9537. Data for each region
   are stored as separate files; these files are contained in directories,
   each of which subtends a 7.5 degree zone of declination.

   File regions.dat gives the vertices (in J2000 coordinates) for each of the
   9537 catalog regions. The requirement for efficient random access to
   small areas of the sky (e.g., circles 0.5 to 1.0 degrees in diameter)
   underlies the adopted catalog organization, which divides the sky into
   large regions, approximately 7.5 deg in size, which are then subdivided
   into small regions on the basis of their expected individual stellar
   populations; each small region corresponds to one file of the GSC. The
   parameters are selected such that small regions nominally contain 2000
   objects; and since the regions are defined entirely by celestial
   geometry, any area can be accessed by reference to a small number of
   regions identifiable with simple logic. The details of this scheme are
   given in Paper III.

   The declination boundaries of the large regions are small circles of
   right ascension taken at 7.5 deg intervals beginning at declination +90
   deg. Each of these declination bands is subdivided in right ascension by
   segments of great circles of declination spaced at intervals of 360/N
   deg, where N is the nearest integer to 48/cos(DEC_0), DEC_0 being the
   center of the declination band. There are 732 large regions in the GSC.
   Finally each large region is divided into small regions by the segments
   of N great circles of declination, uniformly spaced in right ascension,
   and by N small circles of right ascension, uniformly spaced in
   declination. The values of N range from 2 near the galactic poles to 4
   in the plane, and there are 9537 small regions in the GSC. Large region
   numbers are numbered first (most rapidly) by right ascension, beginning
   with the regions whose southwest corner is at RA = 0 and DEC = 0, then
   proceeding north by bands of declination, until the polar zone is
   counted; then the process continues symmetrically in the south,
   beginning at the northwest corner of the region at RA= 0 and DEC = 0.
   Small regions are numbered in the same manner, except that the count
   goes through all the small regions of a large region before proceeding to
   the small regions of the next large region.

   The right ascension and declination limits of each of the 9537 small
   regions, in J2000 coordinates, are given in the table an ASCII version
   of this table is given in regions.dat. The user is cautioned that,
   according to the nomenclature convention explained in Paper III,
   maintenance procedures may result in an object being located up to a few
   seconds outside the tabulated geometric boundaries of its regions;
   therefore, a commensurate expansion of search areas is often appropriate
   in determining the catalog regions to be used. However, this version (1)
   of the GSC does not contain any occurrences of overlapping region
   boundaries.

   All data files (i.e., with the exception of this ReadMe file and the
   directory files) except regions.dat are in FITS (Flexible Image
   Transport System; Greisen et al. 1981; Wells et al. 1981; Grosbol et al.
   1988; and Jahreiss et al. 1992) table format.

   The root directory contains the following files:
      ReadMe - this file
      GSC - Directory for the binary compressed version of the GSC (300Mbytes)
      TABLES - Directory for GSC supporting tables.
      regions.dat - The corners of each small region.

   Directory GSC contains a compact version of the Guide Star Catalogue
   (details in the README file of this GSC directory), and includes
   directories for the 7.5 degree zones in declination; these directories
   in turn contain the GSC region files in a compacted format (usable
   on any architecture with the provided programs, see the README file
   therein), with file identifiers of the form nnnn.GSC, where nnnn is
   the 4-digit decimal region number, with leading zeroes used as
   required to fill the field. The directories are named as follows:

      Directory     Declination         Region
                      From To           From To
      ------------------------------------------
      N0000       +00D 00' +07D 30'    0001 0593
      N0730       +07D 30' +15D 00'    0594 1177
      N1500       +15D 00  +22D 30'    1178 1728
      N2230       +22D 30' +30D 00'    1729 2258
      N3000       +30D 00' +37D 30'    2259 2780
      N3730       +37D 30' +45D 00'    2781 3245
      N4500       +45D 00' +52D 30'    3246 3651
      N5230       +52D 30' +60D 00'    3652 4013
      N6000       +60D 00' +67D 30'    4014 4293
      N6730       +67D 30' +75D 00'    4294 4491
      N7500       +75D 00' +82D 30'    4492 4614
      N8230       +82D 30' +90D 00'    4615 4662
      S0000       -00D 00' -07D 30'    4663 5259
      S0730       -07D 30' -15D 00'    5260 5837
      S1500       -15D 00' -22D 30'    5838 6411
      S2230       -22D 30' -30D 00'    6412 6988
      S3000       -30D 00' -37D 30'    6989 7522
      S3730       -37D 30' -45D 00'    7523 8021
      S4500       -45D 00' -52D 30'    8022 8463
      S5230       -52D 30' -60D 00'    8464 8839
      S6000       -60D 00' -67D 30'    8840 9133
      S6730       -67D 30' -75D 00'    9134 9345
      S7500       -75D 00' -82D 30'    9346 9489
      S8230       -82D 30' -90D 00'    9490 9537
      ------------------------------------------

File Summary:
--------------------------------------------------------------------------------
 FileName    Lrecl  Records    Explanations
--------------------------------------------------------------------------------
ReadMe         80         .    This file
regions.dat    47      9537    The corners of each small region
bright.plt     18        98    Details of the plates for bright stars
out.sam        63       100    Sample output (out of 25,258,765 positions)
TABLES/*        .        15    FITS GSC supporting tables
GSC/*           .         .    Compact version of GSC (for DOS and Unix)
--------------------------------------------------------------------------------

File Summary (FITS files in the directory TABLES):
--------------------------------------------------------------------------------
comments.tbl          Introduction and general comments.
rev_1_1.tbl           Comments on GSC 1.1 revisions.
plates.tbl            Information on the plates used in the GSC.
process.tbl           Image processing parameters.
astr_cal.tbl          Parameters of astrometric calibrations.
phot_cal.tbl          Parameters of photometric calibrations.
c_up_pop.tbl          Catalog update population statistics.
st_pop.tbl            Population statistics for stars.
ns_pop.tbl            Population statistics for non-stars.
regions.tbl           Boundaries of GSC regions.
c_re_pop.tbl          GSC region population statistics.
lg_reg_x.tbl          Index to large regions.
sm_reg_x.tbl          Index to small regions.
xref_p2r.tbl          Cross-reference table, plates to regions.
xref_r2p.tbl          Cross-reference table, regions to plates.
--------------------------------------------------------------------------------

Byte-by-byte Description of file: regions.dat
--------------------------------------------------------------------------------
 Bytes Format  Units   Label     Explanations
--------------------------------------------------------------------------------
 1- 5  I5      ---     num       Number of region
 7- 8  I2      h       RA0h      Low limit of right ascension, hours (J2000)
10-11  I2      min     RA0m      Low limit of right ascension, minutes (J2000)
13-17  F5.2    s       RA0s      Low limit of right ascension, seconds (J2000)
19-20  I2      h       RA1h      High limit of right ascension, hours (J2000)
22-23  I2      min     RA1m      High limit of right ascension, minutes (J2000)
25-29  F5.2    s       RA1s      High limit of right ascension, seconds (J2000)
   31  A1      ---     DE0-      Low limit of declination, sign (J2000)
32-33  I2      deg     DE0d      Low limit of declination, degrees (J2000)
35-38  F4.1    arcmin  DE0m      Low limit of declination, minutes (J2000)
   40  A1      ---     DE1-      High limit of declination, sign (J2000)
41-42  I2      deg     DE1d      High limit of declination, degrees (J2000)
44-47  F4.1    arcmin  DE1m      High limit of declination, minutes (J2000)
--------------------------------------------------------------------------------

Byte-by-byte Description of file: bright.plt
--------------------------------------------------------------------------------
 Bytes    Format     Units     Label      Explanation
--------------------------------------------------------------------------------
 1- 4      A4        ---       plate      PPD plate identification
 7- 8      A2        ---       region     PPD plate region identification
11-18     F8.3       yr        ep         Mid exposure of PPD plate
-------------------------------------------------------------------------------

Byte-by-byte Description of file: out.sam
--------------------------------------------------------------------------------
   Bytes Format Units   Label     Explanations
--------------------------------------------------------------------------------
   1- 10  I10   ---     GSC      *GSC designation
  12- 20  F9.5  deg     RAdeg     Right ascention in J2000, epoch of plate
  22- 30  F9.5  deg     DEdeg     Declination in J2000, epoch of plate
  33- 36  F4.1  arcsec  PosErr    Mean error on position
  38- 42  F5.2  mag     Pmag      photographic magnitude (see n_Pmag)
  44- 47  F4.2  mag   e_Pmag      photographic magnitude
  49- 50  I2    ---   n_Pmag     *[0,18] Coded passbland for magnitude
      52  I1    ---     Class     [0,3] Class of object (0=star; 3=non-stellar)
  54- 61  F8.3  yr      Epoch     Epoch of position
      63  A1    ---     Mult      [TF] True if multiple object / False otherwise
--------------------------------------------------------------------------------
Note on GSC: the GSC Identification is made of a plate number 
     (5 digits) and star number on the plate (5 digits); note that, 
     in the literature, a dash separates generally the two parts.

Note on n_Pmag: the number designates the following combination
     of emulsion and filter:
           magband emulsion filter
           ------- -------- --------
                 0 IIIaJ    GG395
                 1 IIaD     W12
                 4 (bright star)
                 6 IIaD     GG495
                 8 103aE    Red Plex
                10 IIaD     GG495
                11 103aO    GG400
                18 IIIaJ    GG385
           ------- -------- --------
--------------------------------------------------------------------------------

Acknowledgements:
   The primary authors would like to thank the large number of persons who
   have participated in the Guide Star Selection System and the Guide Star
   Catalog developments over the past years. In addition to the many people
   previously acknowledged, they would like to thank the following who made
   contributions in GSC 1.1:
      by collaboration in merging INCA data into GSC 1.1:
         Daniel Egret and the Hipparcos INCA and Tycho groups;
      for providing astrograph plates for southern bright stars:
         Geoffrey Douglass, Robert Harrington, G. Monderen, and Otto
            Richter;
      by contributing to the GSC 1.0 error discussion or by reporting
       specific errors in GSC 1.0:
         Beatrice Bucciarelli, Daniel Egret, Holland Ford, Peter Garnavich,
         Roberto Gilmozzi, Roberta Humphreys, Mario Lattanzi, William Owen,
         Barry Rappaport, Kavan Ratnatunga, Larry Taff, Patrick Wallace,
         Fred Walter, and Archibald Warnock;
      for pre-mastering the CD-ROMs: Ian Evans; o and by making essential
        contributions to the project's infra- structure:
         Ian Evans;
      and by making essential contributions to the project's
        infrastructure:
         Marian Iannuzzi, Greg McLeskey, Dave Paradise, Don
           Stevens-Rayburn, and Patty Trovinger.

   Finally, special thanks are due to Riccardo Giacconi, Director of the
   Space Telescope Science Institute, for his vision and continuing support
   of this project.

   The Guide Star Catalog is partially based on data obtained at Palomar
   Observatory, operated by the California Institute of Technology; at the
   UK Schmidt Telescope, operated by the UK Science and Engineering
   Research Council and by the Anglo-Australia n Observatory; at the Cerro
   Tololo Inter-American Observatory and the Sacramento Peak Observatory,
   both operated by the Association of Universities for Research in
   Astronomy, Inc., under contract to the National Science Foundation; and
   at the Mount Lemmon Observatory, operated by the University of Arizona.

   The two CD-ROMS from which this catalog was copied contain the Guide
   Star Catalog - Version 1.1, with an issue date of 1 August 1992. The
   Guide Star Catalog (GSC) was prepared by the Space Telescope Science
   Institute (ST ScI), 3700 San Martin Drive, Baltimore, MD 21218, USA. ST
   ScI is operated by the Association of Universities for Research in
   Astronomy, Inc. (AURA), under contract with the National Aeronautics and
   Space Administration (NASA).

   The Astronomical Data Centers (ADCs) thank the Space Telescope Science
   Institute and the Association of Universities for Research in Astronomy
   for permission to archive this catalog. This document is the README.TXT
   file for this catalog slightly reformatted to be consistent with the
   format used by the ADCs with a few additions from other STScI
   publications and the addition of the regions.dat from the FITS file.

References:
   Egret, D., Didelon, P., McLean, B. J., Russell, J. L., and Turon, C.,
      Tycho Input Catalog - Cross-matching the Guide Star Catalog with the
      Hipparcos INCA Data Base, Astron. Astrophys., 258, 217-212 (1992).
      (1992A&A...258..217E ; Catalog )
   Garnavich, P., The Stellar Angular Correlation, Clues to Wide Binary
      Star Properties, dissertation, University of Washington (1991).
   Greisen, E. W., Harten, R. H., An Extension of FITS for Groups of Small
      Arrays of Data, Astron. Astrophys. Suppl. Ser., 44, 371-374 (1981).
   Grenon, M., Mermilliod, M., Mermilliod, J. C., The Hipparcos Input
      Catalogue. III. Photometry, Astron. Astrophys., 258, 88-93 (1992).
   Grosbol, P., Harten, R. H., Greisen, E. W., Wells, D. C., Generalized
      Extensions and Blocking Factors for FITS, Astron. Astrophys. Suppl.
      Ser., 73, 359-364 (1988).
   Harten, R. H., Grosbol, P., Greisen, E. W., Wells, D. C., The FITS
      Tables Extension; Astron. Astrophys. Suppl. Ser., 73, 365-372 (1988).
   Jahreiss, H., Requieme, Y., Argue, A. N., Dommanget, J., Rousseau, M.,
      Lederle, T., Le Poole, R. S., Mazurier, J. M., Morrison, L. V., Nys,
      O., Penston, M. J., Perie, J. P., Prevot, L., Tucholke, H. J., de
      Vegt, C., The Hipparcos Input Catalogue. II. Astrometric Data;
      Astron. Astrophys., 258, 82-87 (1992).
   Jenkner, H., Lasker, B. M., Sturch, C. R., McLean, B. J., Shara, M. M.,
      Russell, J. L., The Guide Star Catalog. III. Production, Database
      Organization, and Population Statistics, Astron. J., 99, 2081-2154
      (1990).
   Lasker, B. M., Sturch, C. R., Lopez, C., Mallama, A. D., McLaughlin, S.
      F., Russell, J. L., Wisniewski, W. Z., Gillespie, B. A., Jenkner, H.,
      Siciliano, E. D., Kenny, D., Baumert, J. H., Goldberg, A. M., Henry,
      G. W., Kemper, E., Siegel, M. J., The Guide Star Photometric Catalog.
      I., Astrophys. J. Suppl., 68, 1-90 (1988).
      (1988ApJS...68....1L ; Catalog )
   Lasker, B. M., Sturch, C. R., McLean, B. J., Russell, J. L., Jenkner,
      H., Shara, M. M., The Guide Star Catalog. I. Astronomical and
      Algorithmic Foundations; Astron. J., 99, 2019-2058 (1990).
   Ratnatunga, K. U., Comparison of GSC Photometry in Three Southern
      Fields; Astron. J., 100, 280-290 (1990AJ....100..280R)
   Russell, J. L., Lasker, B. M., McLean, B. J., Sturch, C. R., Jenkner,
      H., The Guide Star Catalog. II. Photometric and Astrometric
      Calibrations; Astron. J., 99, 2059-2081 (1990).
   Taff, L. G., Lattanzi, M. G., Bucciarelli, B., Two Successful Techniques
      for Schmidt Plate Astrometry; Astrophys. J., 358, 359-369 (1990).
   Taff, L. G., Lattanzi, M. G., Bucciarelli, B., Gilmozzi, R., McLean, B.
      J., Jenkner, H., Laidler, V. G., Lasker, B. M., Shara, M. M., Sturch,
      C. R., Some Comments on the Astrometric Properties of the Guide Star
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(End)            Nancy G. Roman/Gail L. Schneider [SSDOO/ADC]        22-Feb-1996