2,379 research outputs found
An Application of Hierarchical Gaussian Processes to the Detection of Anomalies in Star Light Curves
Dark Matter Direct Detection Signals inferred from a Cosmological N-body Simulation with Baryons
We extract at redshift z=0 a Milky Way sized object including gas, stars and
dark matter (DM) from a recent, high-resolution cosmological N-body simulation
with baryons. Its resolution is sufficient to witness the formation of a
rotating disk and bulge at the center of the halo potential. The phase-space
structure of the central galactic halo reveals the presence of a dark disk
component, that is co-rotating with the stellar disk. At the Earth's location,
it contributes to around 25% of the total DM local density, whose value is
rho_DM ~ 0.37 GeV/cm^3. The velocity distributions also show strong deviations
from pure Gaussian and Maxwellian distributions, with a sharper drop of the
high velocity tail.
We give a detailed study of the impact of these features on the predictions
for DM signals in direct detection experiments. In particular, the question of
whether the modulation signal observed by DAMA is or is not excluded by limits
set by other experiments (CDMS, XENON and CRESST...) is re-analyzed and
compared to the case of a standard Maxwellian halo, in both the elastic and the
inelastic scattering scenarios. We find that the compatibility between DAMA and
the other experiments is improved. In the elastic scenario, the DAMA modulation
signal is slightly enhanced in the so-called channeling region, as a result of
several effects. For the inelastic scenario, the improvement of the fit is
mainly attributable to the departure from a Maxwellian distribution at high
velocity.Comment: 39 page
A CORAVEL radial-velocity monitoring of giant Ba and S stars: spectroscopic orbits and intrinsic variations
This paper provides orbital parameters for 38 barium stars and 10 extrinsic S
stars derived from a decade-long CORAVEL monitoring. Lower bounds on the
orbital period (generally exceeding 10 y) have been obtained for 10 more
systems. Mira S, SC and (Tc-poor) C stars have also been monitored and show
intrinsic radial-velocity variations due to atmospheric phenomena. Tentative
orbital solutions are proposed for 3 stars (S UMa, X Cnc, BD-08:1900) where the
velocity and photometric periods are different. Three stars (RZ Peg, SS Vir and
R CMi) exhibit radial-velocity variations synchronous with the light
variations. Pseudo-orbital solutions have been derived for those stars. In the
case of RZ Peg, a line-doubling phenomenon is observed near maximum light, and
probably reflects the shock wave propagating through the photosphere.Comment: Astronomy & Astrophysics Supplements, 20 pages, 8 figures, 8 tables
(LaTeX). Also available at:
http://obswww.unige.ch/~udry/cine/barium/barium.htm
A Radial Velocity Study of Composite-Spectra Hot Subdwarf Stars with the Hobby-Eberly Telescope
Many hot subdwarf stars show composite spectral energy distributions
indicative of cool main sequence companions. Binary population synthesis (BPS)
models demonstrate such systems can be formed via Roche lobe overflow or common
envelope evolution but disagree on whether the resulting orbital periods will
be long (years) or short (days). Few studies have been carried out to assess
the orbital parameters of these spectroscopic composite binaries; current
observations suggest the periods are long. To help address this problem, we
selected fifteen moderately-bright (V~13) hot subdwarfs with F-K dwarf
companions and monitored their radial velocities (RVs) from January 2005 to
July 2008 using the bench-mounted Medium Resolution Spectrograph on the
Hobby-Eberly Telescope (HET). Here we describe the details of our observing,
reduction, and analysis techniques and present preliminary results for all
targets. By combining the HET data with recent observations from the Mercator
telescope, we are able to calculate precise orbital solutions for three systems
using more than 6 years of observations. We also present an up-to-date period
histogram for all known hot subdwarf binaries, which suggests those with F-K
main sequence companions tend to have orbital periods on the order of several
years. Such long periods challenge the predictions of conventional BPS models,
although a larger sample is needed for a thorough assessment of the models'
predictive success. Lastly, one of our targets has an eccentric orbit, implying
some composite-spectrum systems might have formerly been hierarchical triple
systems, in which the inner binary merged to create the hot subdwarf.Comment: Published in The Astrophysical Journal, Volume 758, Issue 1, article
id. 58 (2012). References updated and Equation (5) corrected. 12 pages, 5
figures, 5 table
EPIC 219217635: A Doubly Eclipsing Quadruple System Containing an Evolved Binary
We have discovered a doubly eclipsing, bound, quadruple star system in the
field of K2 Campaign 7. EPIC 219217635 is a stellar image with that
contains an eclipsing binary (`EB') with d and a second EB with
d. We have obtained followup radial-velocity (`RV')
spectroscopy observations, adaptive optics imaging, as well as ground-based
photometric observations. From our analysis of all the observations, we derive
good estimates for a number of the system parameters. We conclude that (1) both
binaries are bound in a quadruple star system; (2) a linear trend to the RV
curve of binary A is found over a 2-year interval, corresponding to an
acceleration, cm s; (3) small
irregular variations are seen in the eclipse-timing variations (`ETVs')
detected over the same interval; (4) the orbital separation of the quadruple
system is probably in the range of 8-25 AU; and (5) the orbital planes of the
two binaries must be inclined with respect to each other by at least
25. In addition, we find that binary B is evolved, and the cooler and
currently less massive star has transferred much of its envelope to the
currently more massive star. We have also demonstrated that the system is
sufficiently bright that the eclipses can be followed using small ground-based
telescopes, and that this system may be profitably studied over the next decade
when the outer orbit of the quadruple is expected to manifest itself in the ETV
and/or RV curves.Comment: Accepted for publication in MNRA
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