I/271 The Guide Star Catalog, Version 2.2 (GSC2.2) (STScI, 2001)
The Guide Star Catalogue, Version 2.2.01 <Space Telescope Science Institute (STScI) and Osservatorio Astronomico di Torino (2001)>
ADC_Keywords: Surveys ; Positional data ; Magnitudes, photographic ;Morphology Description: The GSC II is an all-sky catalog based on 1" resolution scans of the photographic Sky Survey plates, at two epochs and three bandpasses, from the Palomar and UK Schmidt telescopes (DSS). Positions, magnitudes, and classifications are produced for all objects on each plate. The objects are then loaded into the COMPASS database, where multiple observations of the same object are matched and assigned a unique name. The GSC2.2 is a preliminary version of GSC II generated to support telescope operations at the GEMINI and VLT telescopes. The magnitude limits are 18.5 in photographic F (red) or 19.5 in photographic J (blue) or V. The parameters of the bright objects, overexposed on the Schmidt plates, are taken from the Tycho-2 (I/259) catalog. The final version (GSC 2.3), expected to be released in 2002, will also contain proper motions. Copyright: The GSC-II is copyrighted (c) 2001 by the Association of Universities for Research in Astronomy, Inc.; see the copyright notices from http://www-gsss.stsci.edu/catalogs/gsc/GSC2/GSC2.htm Scientists and educators who are using these data for research, teaching purposes and other non-profit activities may freely use these data and we only request that you acknowledge the source in any publication (see the "Acknowledgements" section below). Commercial use of these data is prohibited without permission. Please contact STScI for further information regarding the different copyright holders. Release Notes and Limitation Notice: (see http://www-gsss.stsci.edu/catalogs/gsc/GSC2/GSC2.htm) * 1 database region, N0102231 (out of 32768, or 0.003% of the sky) is omitted. * As a temporary fix for problems observed at the celestial poles, the plates actually containing the poles were re-reduced with a gnomonic projection, and no correction for refraction was applied. This corrects the observed problems with extra and missing objects, but does put these few plates on a very slightly different system than the rest of the sky. * Photometric and astrometric errors as reported in the GSC2.2.01 are unrealistically large. These errors are intended as indicators for operational use only, and cannot be used for scientific studies. An understanding of the actual size of the errors in the catalog can be obtained by comparing the results to external catalogs. * Very bright objects, i.e., in the bright extrapolated area of the photometric solution, were assigned a magnitude of 99.9, rather than an extrapolated magnitude. Since this is the same value that was used as the NULL value, these magnitudes are indistinguishable from magnitudes that were fainter than the magnitude limit or missing altogether. Most of these objects are replaced by Tycho catalogue stars, but some few remain. * Please note that some object names, and selected exported values, have changed between GSC2.2.0 and GSC2.2.01. This is an unavoidable (and indeed generally desirable) consequence of fixing many of the known problems with GSC2.2.0. For this reason, CASB does not recommend attempting to use data extracted from 2.2.0 together with data extracted from 2.2.01. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file out.sam 139 100 Sample output (out of 455851237 objects)
See also: http://www-gsss.stsci.edu/catalogs/gsc/GSC2/GSC2.htm : the GSC-II Home Page I/254 : The HST Guide Star Catalog, Version 1.2 (Lasker+ 1996) I/259 : The Tycho-2 Catalogue (Hog+ 2000) Byte-by-byte Description of file: out.sam
Bytes Format Units Label Explanations
1- 14 A14 --- GSC2.2 Identification of the object (1) 16- 25 F10.6 deg RAdeg Right Ascension in ICRS (J2000), at "Epoch" 27- 36 F10.6 deg DEdeg Declination in ICRS (J2000) 38- 45 F8.3 yr Epoch Epoch of the position 47- 51 F5.3 arcsec e_RAdeg Mean error on RAdeg (2) 53- 57 F5.3 arcsec e_DEdeg Mean error on DEdeg (2) 59- 63 F5.2 mag Rmag ? Magnitude in F photographic band (red) (6) 66- 69 F4.2 mag e_Rmag ? Mean error on Rmag (2) 71- 75 F5.2 mag Bjmag ? Magnitude in J photographic band (blue) (6) 78- 81 F4.2 mag e_Bjmag ? Mean error on Bjmag (2) 83- 87 F5.2 mag Vmag ? Magnitude in V photographic band (green) (6) 90- 93 F4.2 mag e_Vmag ? Mean error on Vmag (2) 95- 99 F5.2 mag Imag ? Magnitude in N photographic band (6) 102-105 F4.2 mag e_Imag ? Mean error on Imag (2) 110 I1 --- Class [0,5] Object class (3) 112-117 F6.2 pix a Semi-major axis of fitting ellipse 119-122 F4.2 --- e Eccentricity of fitting ellipse 124-128 F5.1 deg aPA Position angle (N thru E) of fitting ellipse 130-137 I8 --- Status Source status flag (4) 138-139 I2 --- Np Number of plates (5)
Note (1): The GSC2 identification is a variable-length string made of 9 to 14 bytes. It is based on a level 6 HTM (Hierarchical Triangular Mesh, a recursive spatial indexing scheme dividing the unit sphere into spherical triangles, the number of triangles at level n being 8x4n (see details about HTM at http://www.sdss.jhu.edu/htm/). The 8 leftmost bytes of the GSC2 identification represents the level-6 HTM triangle identification (level 0 consists of the 8 equilateral triangles N0 to N3 and S0 to S3; each further level is represented by a base-4 digit 0 through 3); digits from 9 and up to 14 represent a sequence number assigned to source upon initial detection, left-adjusted without leading zeroes or blanks. Note (2): the photometric and astrometric errors are unrealistically large, see the "Release Notes" section above. Note (3): the object class is defined as: 0=star 1=Galaxy, 2=Blend 3=Non-star 4=unclassified 5=Defect Note (4): the status code is a 8-digit field encoding the properties of the catalog object. This flag is 999999 for a Tycho object. .......x Centroid type associated with the exported position, as: 0 = barycenter 1 = circular gaussian 2 = elliptical gaussian 3 = FPA-applied barycenter 4 = multicircular 5 = multielliptical 6 = FPA + circular 7 = FPA + elliptical (FPA = Fractional Pixel Allocation) ......x. Quality of exported J magnitude, as: 0 = not present 1 = fit 2 = extrapolated .....x.. Quality of exported F magnitude, as: 0 = not present 1 = fit 2 = extrapolated ....x... Quality of exported V magnitude, as: 0 = not present 1 = fit 2 = extrapolated ...x.... Classification unanimity 0 = mixed vote 2 = unanimous defect 1 = unanimous vote ..x..... Classification voters 0 = more than one 15um scan 2 = more than one 25um scan 1 = one 15um scan 3 = one 25um scan .x...... Processing status 0 = complete processing on all plates 1 = object too big (>2562 pix) on at least one plate x....... Deblending 0 = single object on all plates 1 = deblended object on at least one plate. Note (5): The number of plates on which the object appears; this number may include plate observations that were excluded from the GSC2.2. This number is 0 for a Tycho star. Note (6): In this version of the GSC-II, no Imag exists in the N band; the magnitude limits are 18.5 in Rmag (F) and 19.5 in Bmag or Vmag.
Acknowledgements: The Guide Star Catalogue-II is a joint project of the Space Telescope Science Institute and the Osservatorio Astronomico di Torino. Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, for the National Aeronautics and Space Administration under contract NAS5-26555. The participation of the Osservatorio Astronomico di Torino is supported by the Italian Council for Research in Astronomy. Additional support is provided by European Southern Observatory, Space Telescope European Coordinating Facility, the International GEMINI project and the European Space Agency Astrophysics Division.
(End) Francois Ochsenbein [CDS] 18-Oct-2001
|The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line|