407 research outputs found
Debris disc candidates in systems with transiting planets
Debris discs are known to exist around many planet-host stars, but no debris
dust has been found so far in systems with transiting planets. Using publicly
available catalogues, we searched for infrared excesses in such systems. In the
recently published Wide-Field Infrared Survey Explorer (WISE) catalogue, we
found 52 stars with transiting planets. Two systems with one transiting "hot
Jupiter" each, TrES-2 and XO-5, exhibit small excesses both at 12 and 22
microns at a > 3 sigma level. Provided that one or both of these detections are
real, the frequency of warm excesses in systems with transiting planets of 2-4
% is comparable to that around solar-type stars probed at similar wavelengths
with Spitzer's MIPS and IRS instruments. Modelling suggests that the observed
excesses would stem from dust rings with radii of several AU. The inferred
amount of dust is close to the maximum expected theoretically from a
collisional cascade in asteroid belt analogues. If confirmed, the presence of
debris discs in systems with transiting planets may put important constraints
onto formation and migration scenarios of hot Jupiters.Comment: Accepted for publication in MNRAS Letter
Optically bright Active Galactic Nuclei in the ROSAT-Faint Source Catalogue
To build a large, optically bright, X-ray selected AGN sample we have
correlated the ROSAT-FSC catalogue of X-ray sources with the USNO catalogue
limited to objects brighter than O=16.5 and then with the APS database. Each of
the 3,212 coincidences was classified using the slitless Hamburg spectra. 493
objects were found to be extended and 2,719 starlike. Using both the extended
objects and the galaxies known from published catalogues we built up a sample
of 185 galaxies with O_APS < 17.0 mag, which are high-probability counterparts
of RASS-FSC X-ray sources. 130 galaxies have a redshift from the literature and
for another 34 we obtained new spectra. The fraction of Seyfert galaxies in
this sample is 20 %. To select a corresponding sample of 144 high-probability
counterparts among the starlike sources we searched for very blue objects in an
APS-based color-magnitude diagram. Forty-one were already known AGN and for
another 91 objects we obtained new spectra, yielding 42 new AGN, increasing
their number in the sample to 83. This confirms that surveys of bright QSOs are
still significantly incomplete. On the other hand we find that, at a flux limit
of 0.02 count /-1 and at this magnitude, only 40 % of all QSOs are detected by
ROSAT.Comment: 17 pages, 16 figures, accepted by A&
Photometry of Variable Stars from Dome A, Antarctica
Dome A on the Antarctic plateau is likely one of the best observing sites on
Earth thanks to the excellent atmospheric conditions present at the site during
the long polar winter night. We present high-cadence time-series aperture
photometry of 10,000 stars with i<14.5 mag located in a 23 square-degree region
centered on the south celestial pole. The photometry was obtained with one of
the CSTAR telescopes during 128 days of the 2008 Antarctic winter.
We used this photometric data set to derive site statistics for Dome A and to
search for variable stars. Thanks to the nearly-uninterrupted synoptic
coverage, we find 6 times as many variables as previous surveys with similar
magnitude limits. We detected 157 variable stars, of which 55% are
unclassified, 27% are likely binaries and 17% are likely pulsating stars. The
latter category includes delta Scuti, gamma Doradus and RR Lyrae variables. One
variable may be a transiting exoplanet.Comment: Accepted for publication in the Astronomical Journal. PDF version
with high-resolution figures available at
http://faculty.physics.tamu.edu/lmacri/papers/wang11.pd
The XMM-Newton serendipitous ultraviolet source survey catalogue
The XMM-Newton Serendipitous Ultraviolet Source Survey (XMM-SUSS) is a
catalogue of ultraviolet (UV) sources detected serendipitously by the Optical
Monitor (XMM-OM) on-board the XMM-Newton observatory. The catalogue contains
ultraviolet-detected sources collected from 2,417 XMM-OM observations in 1-6
broad band UV and optical filters, made between 24 February 2000 and 29 March
2007. The primary contents of the catalogue are source positions, magnitudes
and fluxes in 1 to 6 passbands, and these are accompanied by profile
diagnostics and variability statistics. The XMM-SUSS is populated by 753,578 UV
source detections above a 3 sigma signal-to-noise threshold limit which relate
to 624,049 unique objects. Taking account of substantial overlaps between
observations, the net sky area covered is 29-54 square degrees, depending on UV
filter. The magnitude distributions peak at 20.2, 20.9 and 21.2 in UVW2, UVM2
and UVW1 respectively. More than 10 per cent of sources have been visited more
than once using the same filter during XMM-Newton operation, and > 20 per cent
of sources are observed more than once per filter during an individual visit.
Consequently, the scope for science based on temporal source variability on
timescales of hours to years is broad. By comparison with other astrophysical
catalogues we test the accuracy of the source measurements and define the
nature of the serendipitous UV XMM-OM source sample. The distributions of
source colours in the UV and optical filters are shown together with the
expected loci of stars and galaxies, and indicate that sources which are
detected in multiple UV bands are predominantly star-forming galaxies and stars
of type G or earlier.Comment: Accepted for publication in MNRA
A possible architecture of the planetary system HR 8799
HR8799 is a nearby A-type star with a debris disk and three planetary
candidates recently imaged directly. We undertake a coherent analysis of
various portions of observational data on all known components of the system.
The goal is to elucidate the architecture and evolutionary status of the
system. We try to further constrain the age and orientation of the system,
orbits and masses of the companions, as well as the location of dust. From the
high luminosity of debris dust and dynamical constraints, we argue for a rather
young system's age of <50Myr. The system must be seen nearly, but not exactly,
pole-on. Our analysis of the stellar rotational velocity yields an inclination
of 13-30deg, whereas i>20deg is needed for the system to be dynamically stable,
which suggests a probable inclination range of 20-30deg. The spectral energy
distribution is naturally reproduced with two dust rings associated with two
planetesimal belts. The inner "asteroid belt" is located at ~10AU inside the
orbit of the innermost companion and a "Kuiper belt" at >100AU is just exterior
to the orbit of the outermost companion. The dust masses in the inner and outer
ring are estimated to be ~1E-05 and 4E-02 M_earth, respectively. We show that
all three planetary candidates may be stable in the mass range suggested in the
discovery paper by Marois et al. 2008 (between 5 and 13 Jupiter masses), but
only for some of all possible orientations. Stable orbits imply a double
(4:2:1) mean-motion resonance between all three companions. We finally show
that in the cases where the companions themselves are orbitally stable, the
dust-producing planetesimal belts are also stable against planetary
perturbations.Comment: 12 pages, 14 figures, 4 tables, accepted to be published in Astronomy
& Astrophysics (May 20, 2009
Forward Global Photometric Calibration of the Dark Energy Survey
Many scientific goals for the Dark Energy Survey (DES) require calibration of
optical/NIR broadband photometry that is stable in time and uniform
over the celestial sky to one percent or better. It is also necessary to limit
to similar accuracy systematic uncertainty in the calibrated broadband
magnitudes due to uncertainty in the spectrum of the source. Here we present a
"Forward Global Calibration Method (FGCM)" for photometric calibration of the
DES, and we present results of its application to the first three years of the
survey (Y3A1). The FGCM combines data taken with auxiliary instrumentation at
the observatory with data from the broad-band survey imaging itself and models
of the instrument and atmosphere to estimate the spatial- and time-dependence
of the passbands of individual DES survey exposures. "Standard" passbands are
chosen that are typical of the passbands encountered during the survey. The
passband of any individual observation is combined with an estimate of the
source spectral shape to yield a magnitude in the standard
system. This "chromatic correction" to the standard system is necessary to
achieve sub-percent calibrations. The FGCM achieves reproducible and stable
photometric calibration of standard magnitudes of stellar
sources over the multi-year Y3A1 data sample with residual random calibration
errors of per exposure. The accuracy of the
calibration is uniform across the DES footprint to
within . The systematic uncertainties of magnitudes in
the standard system due to the spectra of sources are less than
for main sequence stars with .Comment: 25 pages, submitted to A
A catalog of Kazarian galaxies
The entire Kazarian galaxies (KG) catalog is presented which combines
extensive new measurements of their optical parameters with a literature and
database search. The measurements were made using images extracted from the
STScI Digitized Sky Survey (DSS) of Jpg(blue), Fpg(red) and Ipg(NIR) band
photographic sky survey plates obtained by the Palomar and UK Schmidt
telescopes. We provide accurate coordinates, morphological type, spectral and
activity classes, blue apparent diameters, axial ratios, position angles, red,
blue and NIR apparent magnitudes, as well as counts of neighboring objects in a
circle of radius 50 kpc from centers of KG. Special attention was paid to the
individual descriptions of the galaxies in the original Kazarian lists, which
clarified many cases of misidentifications of the objects, particularly among
interacting systems. The total number of individual Kazarian objects in the
database is now 706. We also include the redshifts which are now available for
404 galaxies and the 2MASS infrared magnitudes for 598 KG. The database also
includes extensive notes, which summarize information about the membership of
KG in different systems of galaxies, and about revised activity classes and
redshifts. An atlas of several interesting subclasses of KG is also presented.Comment: 15 pages, 5 figures, 1 table, Accepted in Astrophysics, Vol. 53, No.
1, 2010 (English translation of Astrofizika
Reproductive Outcomes Following Ectopic Pregnancy: Register-Based Retrospective Cohort Study
Using Scottish national registry data, Sohinee Bhattacharya and colleagues investigate pregnancy outcomes following ectopic pregnancy in comparison to livebirth, miscarriage, or termination in a first pregnancy
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