An Ultraviolet-Excess Optical Candidate for the Luminous Globular Cluster X-ray Source in NGC1851

The intense, bursting X-ray source in the globular cluster NGC 1851 was one of the first cluster sources discovered, but has remained optically unidentified for 25 years. We report here on results from Hubble Space Telescope WFPC2 multicolor images in NGC 1851. Our high spatial resolution images resolve ~200 objects in the 3'' radius Einstein X-ray error circle, 40 times as many as in previous ground-based work. A color-magnitude diagram of the cluster clearly reveals a markedly UV-excess object with B~21, (U-B) ~ -0.9 only 2'' from the X-ray position. The UV-excess candidate is 0.12'' distant from a second, unremarkable star that is 0.5 mag brighter in B; thus ground-based studies of this field are probably impractical. Three other UV-excess objects are also present among the ~16,000 objects in the surveyed region of the cluster, leaving a ~5% probability that a UV-excess object has fallen in the X-ray error circle by chance. No variability of the candidate is seen in these data, although a more complete study is required. If this object is in fact the counterpart of the X-ray source, previous inferences that some globular cluster X-ray sources are optically subluminous with respect to low-mass X-ray binaries in the field are now strengthened.Comment: 13 pages including 1 table and 3 figures in AASTeX 4.0; To appear in The Astrophysical Journal Letters, volume 472 (1996 December 1). Preprint with full-resolution figures available at http://www.astro.washington.edu/deutsch/pubs/pubs.htm

A Catalog and Atlas of Cataclysmic Variables: The Final Edition

The Catalog and Atlas of Cataclysmic Variables has been a staple of the CV community for over 10 years. The catalog has grown from 751 CVs in 1993 to 1600 CVs at present. The catalog became a ``living'' edition in 2001, and its contents have been continually updated since that time. Effective 27 January 2006, the catalog will transition to an archival site, with no further updates to its contents. While it is antipicated that the site will remain active, we present the complete contents of the site as a precaution against a loss of the on-line data.Comment: 8 pages, including 6 table

Time-Resolved Ultraviolet Observations of the Globular Cluster X-ray Source in NGC 6624: The Shortest Known Period Binary System

Using the Faint Object Spectrograph (FOS) aboard the Hubble Space Telescope, we have obtained the first time-resolved spectra of the King et al. ultraviolet-bright counterpart to the 11-minute binary X-ray source in the core of the globular cluster NGC 6624. This object cannot be readily observed in the visible, even from HST, due to a much brighter star superposed <0.1'' distant. Our FOS data show a highly statistically significant UV flux modulation with a period of 11.46+-0.04 min, very similar to the 685 sec period of the known X-ray modulation, definitively confirming the association between the King et al. UV counterpart and the intense X-ray source. The UV amplitude is very large compared with the observed X-ray oscillations: X-ray variations are generally reported as 2-3% peak-to-peak, whereas our data show an amplitude of about 16% in the 126-251 nm range. A model for the system by Arons & King predicts periodic UV fluctuations in this shortest-known period binary system, due to the cyclically changing aspect of the X-ray heated face of the secondary star (perhaps a very low mass helium degenerate). However, prior to our observations, this predicted modulation has not been detected. Employing the Arons & King formalism, which invokes a number of different physical assumptions, we infer a system orbital inclination 35deg<i<50 deg. Amongst the three best-studied UV/optical counterparts to the intense globular cluster X-ray sources, two are now thought to consist of exotic double-degenerate ultrashort period binary systems.Comment: 10 pages including 2 figures in Latex (AASTeX 4.0). Accepted for publication in vol. 482 (1997 June 10 issue) of The Astrophysical Journal (Letters

A Catalog and Atlas of Cataclysmic Variables - The Living Edition

The Catalog and Atlas of Cataclysmic Variables (Edition 1 - 1993) and Edition 2 - 1997) has been a valuable source of information for the cataclysmic variable (CV) community. However, the goal of having a central location for all objects is slowly being lost as each new edition is generated. There can also be a long time delay between new information becoming available on an object and its publication in the catalog. To eliminate these concerns, as well as to make the catalog more accessible, we have created a web site which will contain a ``living'' edition of the catalog. We have also added orbital period information, as well as finding charts for novae, to the catalog.Comment: LaTeX, 8 pages, 4 ps-figures, accepted by PAS

Far-Ultraviolet Observations of RR Lyrae Stars in the Core of NGC 1851

There are extraordinarily few far ultraviolet observations of RR Lyrae stars in the literature. We present Hubble Space Telescope FUV (~1600 A) imaging of the core of the globular cluster NGC 1851. Eleven new variables whose light curves are consistent with those of RR Lyr stars are discovered, increasing the total number of RR Lyr known in this cluster by a substantial amount. In agreement with basic physical theory, the observed amplitude of the variables in the FUV is enormous compared with the century of past optical observations, ranging up to 4 mag. HST STIS FUV observations of cluster cores may prove an especially effective means of obtaining a near-complete census of RR Lyr stars, combining high angular resolution, suppression of luminous red stars, and data where the stellar pulsation amplitudes are greatly enhanced. Attention is also drawn to a peculiar blue object in the cluster that is most probably a low mass x-ray binary system in quiescence.Comment: Accepted for publication in The Astronomical Journal, Vol. 128, Nov. 2004, 13 pages, 4 figures, AASTeX v5.