5.2. Object Catalogues and Finding Charts from DSS
The HST Guide Star Catalog (GSC) was the first all-sky catalogue of optical objects extracted from plate digitizations. For declinations north of +3° the Palomar ``Quick-V'' (epoch 1982) plates of 20min exposure were used. For the south the 50-75min exposures of the SERC BJ survey (epoch ~ 1975) and its equatorial extension (epoch ~ 1982) were used (see www-gsss.stsci.edu/gsc/gsc12/description.html). The GSC contains ~ 19 106 objects in the range 6-15 mag. Most of them are stars, but an estimated 5 106 galaxies are present as well. The positional accuracy has been improved to better than 0.4'' in version 1.2. Note, however, that this catalogue is not magnitude-limited, but that the selection of stars has been carried out so as to provide a homogeneous density of guide stars over the sky.
The Automated Plate Measuring Machine (APM) is located at the Institute of Astronomy, Cambridge, UK and has been used to prepare object catalogues from Sky Survey plates at high Galactic latitudes (|b| > 20°), see e.g. [Lewis & Irwin (1996)]. Both colours of the POSS-I survey plates were scanned and the objects cross-identified, so that colour information is available for a matched object catalogue of well over 100 million objects down to m = 21.5 in blue (O) and m = 20 in red (E). For the southern sky the glass plates of the UKST BJ and later the UKST SES-R survey have been scanned, with limiting magnitudes of 22.5 in BJ and 21 in R. All plates were scanned at 0.5'' scan interval and a scanning resolution of 1''. The pixel data of the scans are not available, and no copies of the entire catalogue are distributed. Both the northern hemisphere catalogue ( > -3° ), and the southern hemisphere catalogue based on UKST BJ and SES-R plates (~ 50% complete) are available for routine interrogation at www.ast.cam.ac.uk/~apmcat. The URL www.aao.gov.au/local/www/apmcatbin/forms offers a standalone client program in C (apmcat.c) which allows queries for large sets of finding charts and object lists from the command line. The catalogues can also be accessed from a captive account (telnet 188.8.131.52, login as catalogues and follow the instructions).
COSMOS (COordinates, Sizes, Magnitudes, Orientations, and Shapes) is a plate scanning machine at the Royal Observatory Edinburgh, which was used to scan the whole southern sky ( < + 2.5°) from the IIIa-J and Short Red Surveys, and led to an object catalogue of several hundred million objects ([Drinkwater et al. (1995)]). Public access to the catalogue is provided through the Anglo-Australian Observatory (AAO) at www.aao.gov.au/htdocs/local/www/apmcatbin/cosmos/index.html, and through the Naval Research Laboratory (NRL) at xweb.nrl.navy.mil/www_rsearch/RS_form.html. The AAO facility requires the user to register and obtain a password. During a telnet session the user may either input coordinates on the fly, or have them read from a file previously transferred (via ftp) to the public AAO account, and create charts and/or object lists on various different output media. The user has to transfer the output back to the local account via ftp. This disadvantage is balanced by the possibility of extracting large amounts of charts for big cross-identification projects. Charts may be requested in stamp-size format resulting in PostScript files containing many charts per page.
The US Naval Observatory (USNO) has scanned the POSS I E- and O-plates (for plate centres with - 30°) and the ESO-R and SERC-J plates (centred at - 35°) with the ``Precision Measuring Machine'' (PMM). A scan separation of 0.9'' was used (i.e. finer than that of the STScI scans for DSS), and object fitting on these images resulted in the USNO-A1.0 catalogue of 488,006,860 objects down to the very plate limit (limiting mag O = 21, E = 20, J = 22, F = 21). Objects were accepted only if present to within 2'' on both E- and O-plates, which implies an efficient rejection of plate faults, but also risks losing real, faint objects with extreme colours. This catalogue is available both as a set of 10 CD-ROMs and interactively at psyche.usno.navy.mil/pmm. Client programs at CDS (Section 3) and ESO (archive.eso.org/skycat/servers/usnoa) allow extraction of object lists of small parts of the sky very rapidly from the command line. There are plans to produce a USNO-B catalogue, which will combine POSS-I and POSS-II in the north, UKST BJ, ESO-R, and AAO-R in the south, and will attempt to add proper motions and star/galaxy separation fields to the catalogue.
The images from the APS scans of POSS-I (see above) have been used to prepare a catalogue of ~ 109 stellar objects and 106 galaxies detected on both E and O plates. Extractions from this catalogue may be drawn from aps.umn.edu/homepage.aps.html, or from the ADS catalogue service at adswww.harvard.edu/ads_catalogs.html.