The Second-Generation Guide Star Catalog: Description and Properties

The GSC-II is an all-sky database of objects derived from the uncompressed DSS that the STScI has created from the Palomar and UK Schmidt survey plates and made available to the community. Like its predecessor (GSC-I), the GSC-II was primarily created to provide guide star information and observation planning support for HST. This version, however, is already employed at some of the ground-based new-technology telescopes such as GEMINI, VLT, and TNG, and will also be used to provide support for the JWST and Gaia space missions as well as LAMOST, one of the major ongoing scientific projects in China. Two catalogs have already been extracted from the GSC-II database and released to the astronomical community. A magnitude-limited (R=18.0) version, GSC2.2, was distributed soon after its production in 2001, while the GSC2.3 release has been available for general access since 2007. The GSC2.3 catalog described in this paper contains astrometry, photometry, and classification for 945,592,683 objects down to the magnitude limit of the plates. Positions are tied to the ICRS; for stellar sources, the all-sky average absolute error per coordinate ranges from 0.2" to 0.28" depending on magnitude. When dealing with extended objects, astrometric errors are 20% worse in the case of galaxies and approximately a factor of 2 worse for blended images. Stellar photometry is determined to 0.13-0.22 mag as a function of magnitude and photographic passbands (B,R,I). Outside of the galactic plane, stellar classification is reliable to at least 90% confidence for magnitudes brighter than R=19.5, and the catalog is complete to R=20.Comment: 52 pages, 33 figures, to be published in AJ August 200

Close-Binary Nuclei of Planetary Nebulae

Close-binary planetary-nebula nuclei (PNNs) provide direct evidence for occurrence of a common-envelope phase in binary-star evolution. Their descendants are V471 Tauri-type detached binaries, cataclysmic binaries, and possibly Type I supernovae. Thirteen close-binary PNNs are now known from periodic photometric or radial-velocity variations, or from composite optical/UV spectra. At least 10% of PNNs are close binaries, a fraction more than sufficient to account for the formation of all of the cataclysmic variables in the solar neighborhood. The Abell 35-type binary PNNs, a class with three known members, contain rapidly rotating, chromospherically active late-type primary stars along with extremely hot companions detected with the IUE satellite.</jats:p

The Abell 35-Type Planetary Nuclei

The nuclei of the low-surface-brightness PNe A 35, LoTr 1, and LoTr 5 are binaries containing rapidly rotating late-type subgiants or giants and extremely hot (Teff ≳ 100,000 K) companions detected by the IUE satellite. All three objects show low-amplitude, periodic photometric variations in the optical band (with periods of 0.76 or 3.3, 6.6, and 5.9 days, respectively).</jats:p