266 research outputs found
Trigonometric Parallaxes of Central Stars of Planetary Nebulae
Trigonometric parallaxes of 16 nearby planetary nebulae are presented,
including reduced errors for seven objects with previous initial results and
results for six new objects. The median error in the parallax is 0.42 mas, and
twelve nebulae have parallax errors less than 20 percent. The parallax for
PHL932 is found here to be smaller than was measured by Hipparcos, and this
peculiar object is discussed. Comparisons are made with other distance
estimates. The distances determined from these parallaxes tend to be
intermediate between some short distance estimates and other long estimates;
they are somewhat smaller than estimated from spectra of the central stars.
Proper motions and tangential velocities are presented. No astrometric
perturbations from unresolved close companions are detected.Comment: 24 pages, includes 4 figures. Accepted for A
Parametrization and Classification of 20 Billion LSST Objects: Lessons from SDSS
The Large Synoptic Survey Telescope (LSST) will be a large, wide-field
ground-based system designed to obtain, starting in 2015, multiple images of
the sky that is visible from Cerro Pachon in Northern Chile. About 90% of the
observing time will be devoted to a deep-wide-fast survey mode which will
observe a 20,000 deg region about 1000 times during the anticipated 10
years of operations (distributed over six bands, ). Each 30-second long
visit will deliver 5 depth for point sources of on average.
The co-added map will be about 3 magnitudes deeper, and will include 10 billion
galaxies and a similar number of stars. We discuss various measurements that
will be automatically performed for these 20 billion sources, and how they can
be used for classification and determination of source physical and other
properties. We provide a few classification examples based on SDSS data, such
as color classification of stars, color-spatial proximity search for wide-angle
binary stars, orbital-color classification of asteroid families, and the
recognition of main Galaxy components based on the distribution of stars in the
position-metallicity-kinematics space. Guided by these examples, we anticipate
that two grand classification challenges for LSST will be 1) rapid and robust
classification of sources detected in difference images, and 2) {\it
simultaneous} treatment of diverse astrometric and photometric time series
measurements for an unprecedentedly large number of objects.Comment: Presented at the "Classification and Discovery in Large Astronomical
Surveys" meeting, Ringberg Castle, 14-17 October, 200
The USNO-B Catalog
USNO-B is an all-sky catalog that presents positions, proper motions,
magnitudes in various optical passbands, and star/galaxy estimators for
1,042,618,261 objects derived from 3,643,201,733 separate observations. The
data were obtained from scans of 7,435 Schmidt plates taken for the various sky
surveys during the last 50 years. USNO-B1.0 is believed to provide all-sky
coverage, completeness down to V = 21, 0.2 arcsecond astrometric accuracy at
J2000, 0.3 magnitude photometric accuracy in up to five colors, and 85%
accuracy for distinguishing stars from non-stellar objects. A brief discussion
of various issues is given here, but the actual data are available from
http://www.nofs.navy.mil and other sites.Comment: Accepted by Astronomical Journa
Swift/XRT follow-up observations of TeV sources of the HESS Inner Galaxy survey
In order to provide a firm identification of the newly discovered Galactic
TeV sources, a search for counterparts in a broad band from soft X-ray to soft
gamma-rays is crucial as data in these wavebands allow us to distinguish
between different types of suggested models (for example leptonic versus
hadronic) and, in turn, to disentangle their nature. In this paper, we report
the results of a set of follow-up observations performed by the Swift/X-Ray
Telescope (XRT) on seven sources recently discovered by HESS, in the range from
few hundred GeV to about 10 TeV, during the inner Galaxy survey (Aharonian et
al. 2006). In all, but one case, we detect X-ray sources inside or close-by the
extended TeV emitting region. All these putative X-ray counterparts have
accurate arc-second location and are consistent with being point sources. The
main result of our search is the discovery that three of them are located at
the center of the diffuse radio emission of the supernova remnants, which have
been spatially associated to these TeV objects. HESS J1640-465, HESS J1834-087
and HESS J1813-178 show this evidence, suggestive of a possible Pulsar Wind
Nebula association.Comment: 22 pages, 6 figures, accepted for publication on The Astrophysical
Journa
The first WASP public data release
The WASP (wide angle search for planets) project is an exoplanet transit survey that has been automatically taking wide field images since 2004. Two instruments, one in La Palma and the other in South Africa, continually monitor the night sky, building up light curves of millions of unique objects. These light curves are used to search for the characteristics of exoplanetary transits. This first public data release (DR1) of the WASP archive makes available all the light curve data and images from 2004 up to 2008 in both the Northern and Southern hemispheres. A web interface () to the data allows easy access over the Internet. The data set contains 3 631 972 raw images and 17 970 937 light curves. In total the light curves have 119 930 299 362 data points available between them
Variable stars in the field of the old open cluster Melotte 66
We report the results of photometric monitoring of the Melotte 66 field in
BVI filters. Ten variables were identified with nine being new discoveries. The
sample includes eight eclipsing binaries of which four are W UMa type stars,
one star is a candidate blue straggler. All four contact binaries are likely
members of the cluster based on their estimated distances. Ten blue stars with
U-B<-0.3 were detected inside a 14.8 x 22.8 arcmin^2 field centred on the
cluster. Time series photometry for 7 of them showed no evidence for any
variability. The brightest object in the sample of blue stars is a promising
candidate for a hot subdwarf belonging to the cluster. We show that the
anomalously wide main sequence of the cluster, reported in some earlier
studies, results from a combination of two effects: variable reddening occuring
across the cluster field and the presence of a rich population of binary stars
in the cluster itself. The density profile of the cluster field is derived and
the total number of member stars with 16<V<21 or 2.8<M_{V}<7.8 is estimated
conservatively at about 1100.Comment: 8 pages, 12 figures, accepted to MNRAS - 29 June 200
Identification of new cataclysmic variables in the 1RXS and USNO-B1.0 catalogs
As a result of applying the original optical variability search method on
publicly available data, we have found eight new cataclysmic variables and two
possible Optically Violent Variable quasars among the previously unidentified
X-ray sources in the ROSAT catalog. We describe the search method and present
the characteristics of the newly identified variable stars. The obtained
results demonstrate the large potential of the concept of Virtual Observatory
for identifying new objects of astrophysical interest.Comment: 16 pages, 11 figures, 2 tables; submitted to Astronomy Letter
- …