135 research outputs found
CC Bootis: QSO, Not Variable Halo Giant
The poorly-studied, faint (18<m_pg<19.5) variable star CC Bootis has been
noted in the literature as a candidate for a halo red giant. It proves instead
to be a quasi-stellar object of redshift z=0.172, and is detected as an X-ray
source by ROSAT. In addition to its odd heritage, CC Boo exhibits unusually
high amplitude optical variability for an optically-selected QSO.Comment: 6 pages including 1 table and 2 figures; Accepted for publication in
Pub. Astr. Soc. Pacific, Vol 109, June 199
Observations made with the International Ultraviolet Explorer
Observations were made with the International Ultraviolet Explorer of two quite diverse astronomical objects. The first is an extremely ultraviolet excess star projected near the globular cluster M5. The second is a previously unrecognized but very bright starburst galaxy. Each of these objects is discussed in detail
Related investigations on the physics of high energy emission from active galactic nuclei
The Final Technical Report on a number of related investigations on the physics of high energy emission from active galactic nuclei, such as Seyfert galaxies and quasi-stellar objects is presented. The chief conclusions of the work are briefly described, and citations to the papers supported by this grant and published in the refereed scientific literature are provided. Areas of research included: 'warm' galaxies observed in x rays; x ray/infrared correlations in galaxies; the contribution of active galaxies to the cosmic x ray background radiation; and an unusual x ray emitting starburst galaxy
Photometry of GX 349+2: Evidence for a 22-hour Period
The intense galactic X-ray source GX 349+2 (Sco X-2) belongs to the class of
persistently bright low-mass X-ray binaries called Z-sources. GX 349+2,
although observed in X-rays for more than 30 years, has only recently been
optically identified with a 19th mag star. Of the six known Z-sources, only two
(Sco X-1 and Cyg X-2) have been studied in the optical. It has been suggested
that Z-sources as a group are characterized by evolved companions and
correspondingly long orbital periods (Sco X-1, P=0.8 d; Cyg X-2, P=9.8 d).
Recently Southwell et al. (1996) have presented spectroscopic observations of
GX 349+2 suggesting a 14 d orbital period. We have obtained broadband
photometry of the system on six consecutive nights, and find a statistically
significant 21.85 +/- 0.4 h (3 sigma) period of 0.14 mag half-amplitude,
superposed on erratic flickering typical of Sco X-1 type objects. As with other
Z-sources, caution will be needed to insure that the variations are truly
periodic, and not simply due to chaotic variability observed over a relatively
short time span. Depending on the origin of the brightness variations, our
proposed period could be either the orbital or half the orbital period. If our
period is confirmed, then the nature of the 14 d spectroscopic variation found
by Southwell et al. (1996) is unclear. There is evidence that the mass function
of GX 349+2 is similar to that of Sco X-1.Comment: 17 pages including 3 tables and 5 figures; Uses AASTeX 4.0; Accepted
for publication in The Astronomical Journal, volume 112, December 199
The Recognition of Unusual Objects in the Sloan Digital Sky Survey Color System
We present 5 filter photometry of 21 carbon stars, 15 asteroids, 15
cataclysmic variables, 6 metal-poor stars, 5 Cepheids, 1775 field stars, blue
horizontal branch (BHB) stars and RR Lyrae stars in the globular clusters M 15
and M 2, two primary standards, and 19 secondary standards. The photometry was
carried out using a filter set identical to that which will be used for the
Sloan Digital Sky Survey. We find that carbon stars, CVs, R-type, J-type, and
V-type asteroids, BHB stars, and RR Lyr stars should be identifiable on the
basis of SDSS photometry alone, while Cepheids, metal-poor stars, and many
types of asteroids are indistinguishable from the stellar locus of field stars.Comment: 44 pages, 13 postscript figures. Accepted for publication in
Publications of the Astronomical Society of the Pacific, vol. 110, November
1998. Uses AAS Latex style file, version 4.
A Census of Object Types and Redshift Estimates in the SDSS Photometric Catalog from a Trained Decision-Tree Classifier
We have applied ClassX, an oblique decision tree classifier optimized for
astronomical analysis, to the homogeneous multicolor imaging data base of the
Sloan Digital Sky Survey (SDSS), training the software on subsets of SDSS
objects whose nature is precisely known via spectroscopy. We find that the
software, using photometric data only, correctly classifies a very large
fraction of the objects with existing SDSS spectra, both stellar and
extragalactic. ClassX also accurately predicts the redshifts of both normal and
active galaxies in SDSS. To illustrate ClassX applications in SDSS research, we
(a) derive the object content of the SDSS DR2 photometric catalog and (b)
provide a sample catalog of resolved SDSS objects that contains a large number
of candidate AGN galaxies, 27,000, along with 63,000 candidate normal galaxies
at magnitudes substantially fainter than typical magnitudes of SDSS
spectroscopic objects. The surface density of AGN selected by ClassX to i~19 is
in agreement with that quoted by SDSS. When ClassX is applied to the
photometric data fainter than the SDSS spectroscopic limit, the inferred
surface density of AGN rises sharply, as expected. The ability of the
classifier to accurately constrain the redshifts of huge numbers (ultimately ~
10^7) of active galaxies in the photometric data base promises new insights
into fundamental issues of AGN research, such as the evolution of the AGN
luminosity function with cosmic time, the starburst--AGN connection, and
AGN--galactic morphology relationships.Comment: Accepted for publication in The Astronomical Journal, Vol. 130, 2005;
33 pages, 10 figures, 5 tables, AASTeX v5.0. Table 5 will be electronic in
the published journal, but available now at
http://www-int.stsci.edu/~margon/table5.ascii and
http://www-int.stsci.edu/~margon/table5.ascii.g
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
Complex Velocity Fields in the Shell of T Pyxidis
We present spatially-resolved, moderate-resolution spectrophotometry of the
recurrent nova T Pyx and a portion of the surrounding shell. The spectrum
extracted from a strip of width 10'' centered on the star shows well-known,
strong emission lines typical of old novae, plus a prominent, unfamiliar
emission line at 6590 Angstroms. This line, and a weaker companion at 6540
Angstroms which we also detect, have been previously reported by Shahbaz et
al., and attributed to Doppler-shifted H alpha emission from a collimated jet
emerging from T Pyx. We demonstrate that these lines are instead due to [NII]
6548, 6584 from a complex velocity field in the surrounding nebula. The
comments of past workers concerning the great strength of HeII 4686 in T Pyx
itself are also reiterated.Comment: 8 pages including 2 figures; Accepted for publication in The
Astrophysical Journal Letter
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