The Yale University Observatory announces the publication of a completely revised and enlarged two-volume edition of the General Catalogue of Trigonometric Stellar Parallaxes containing 15,994 parallaxes for 8,112 stars published before the end of 1995. In this Fourth Edition, 1,722 (27%) new stars have been added to those contained in the previous edition by Jenkins (1963). The mode of the parallax accuracy for the newly added stars (0.004" s.e .) is considerably better than in the previous editions (about 0.016"). Approximately half of the newly added stars are fainter than the Hipparcos Astrometric Satellite's magnitude limit of 13.0, while approximately 2300 stars in The Parallax Catalogue are not in the Hipparcos Catalogue.
Volume I contains a 29-page Introduction describing the project and a summary of the analysis of the accidental and systematic errors of the parallaxes. Those results provide a "system" for the Catalogue which then yields weighted absolute parallaxes for each star. Following the Introduction, on each left-hand page a commonly used name is listed, along with the equatorial coordinates in the system of the FK4 for 1900 and the secular variation for 100 years to aid in quickly transferring from 1900 to 2000. Transit tables at the end of Vol. I are provided to assist the user in locating stars with coordinates at the equinox of 1950 or 2000. The 1900 equinox has been maintained to avoid assigning yet another star number. Following the coordinates, proper motions are given along with the weighted average absolute parallaxes, parallax error, number of parallax observations and a quality code. The right-hand page adds the UBV photometry, MK spectral types, cross identifications with the Bright Star Catalogue, HD, DM, CNS, variable star name, ADS/WDS and another star name. An appendix lists the stars in decreasing order of parallax.
Volume II contains for each star, all published parallaxes, associated errors and sources of publication, the average magnitude of the reference frame, galactic coordinates, the correction to absolute parallax based on an improved model of the Galaxy, absolute parallax and its error and the weight of the parallax. The right-hand page contains a Section with the Notes to the Catalogue, including additional cross-identifications, data on the variability and binary nature of the stars, and other information that might be of general interest. Another Section contains Double Star information including the ADS number, the star's common double star name, magnitudes of the components, separation and position angle, and when an orbit is available, the semi-major axis and period of the binary.
Printed copies of the Two-volume General Catalogue are available from the Yale University Observatory, while a condensed computer readable version of Volume I without the Introduction and Appendices will be available soon from the Astronomical Data Center (ADC) at Goddard Space Flight Center (also on a CD ROM disk soon to be released) and from the Strasbourg Stellar Data Center (CDS) in France. Volume II will not be available on the CD ROM disk nor in computer readable form. A CD ROM disk was issued by the ADC in 1991 which contained a preliminary version of the YPC. In this final version we have revised the weighting system, and included newly published parallaxes, photometry and spectral types for most of the stars. The weighted mean parallaxes of many stars will be found to differ from those in the preliminary version due to changes in the weighting system, revisions to the default reference star magnitudes and the addition of new data.
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