139 research outputs found
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.
- …