209 research outputs found
The Penn State - Toru\'n Planet Search: target characteristics and recent results
More than 450 stars hosting planets are known today but only approximately 30
planetary systems were discovered around stars beyond the Main Sequence. The
Penn State-Toru\'n Planet Search, putting an emphasis on extending studies of
planetary system formation and evolution to intermediate-mass stars, is
oriented towards the discoveries of substellar-mass companions to a large
sample of evolved stars using high-precision radial velocity technique. We
present the recent status of our survey and detailed characteristic for ~350
late type giant stars, i.e. the new results of radial velocity analysis and
stellar fundamental parameters obtained with extensive spectroscopic method.
Moreover, in the future we will make an attempt to perform the statistical
study of our sample and searching the correlations between the existence of
substellar objects and stellar atmospheric parameters according to previous
works which investigated the planetary companion impact on the evolution of the
host stars.Comment: 7 pages, 5 figures, proceeding of the conference "Planetary Systems
beyond the Main Sequence" (Bamberg, Germany, August 11-14, 2010) edited by S.
Schuh, H. Drechsel and U. Heber, AIP Conference Series, part of
PlanetsbeyondMS/2010 proceedings http://arxiv.org/html/1011.660
Planets Around the K-Giants BD+20 274 and HD 219415
We present the discovery of planet-mass companions to two giant stars by the
ongoing Penn State- Toru\'n Planet Search (PTPS) conducted with the 9.2 m
Hobby-Eberly Telescope. The less massive of these stars, K5-giant BD+20 274,
has a 4.2 MJ minimum mass planet orbiting the star at a 578-day period and a
more distant, likely stellar-mass companion. The best currently available model
of the planet orbiting the K0-giant HD 219415 points to a Jupiter-mass
companion in a 5.7-year, eccentric orbit around the star, making it the longest
period planet yet detected by our survey. This planet has an amplitude of
\sim18 m/s, comparable to the median radial velocity (RV) "jitter", typical of
giant stars.Comment: 5 figures, 13 pages, accepted by the Astrophysical Journal. arXiv
admin note: substantial text overlap with arXiv:1110.164
A New Planet Around an M Dwarf: Revealing a Correlation Between Exoplanets and Stellar Mass
We report precise Doppler measurements of GJ317 (M3.5V) that reveal the
presence of a planet with a minimum mass Msini = 1.2 Mjup in an eccentric,
692.9 day orbit. GJ317 is only the third M dwarf with a Doppler-detected Jovian
planet. The residuals to a single-Keplerian fit show evidence of a possible
second orbital companion. The inclusion of an additional Jupiter-mass planet (P
= 2700 days, Msini = 0.83 Mjup) improves the quality of fit significantly,
reducing the rms from 12.5 m/s to 6.32 m/s. A false-alarm test yields a 1.1%
probability that the curvature in the residuals of the single-planet fit is due
to random fluctuations, lending additional credibility to the two-planet model.
However, our data only marginally constrain a two-planet fit and further
monitoring is necessary to fully characterize the properties of the second
planet. To study the effect of stellar mass on Jovian planet occurrence we
combine our samples of M stars, Solar-mass dwarfs and intermediate-mass
subgiants. We find a positive correlation between stellar mass and the
occurrence rate of Jovian planets within 2.5 AU; the former A-type stars in our
sample are nearly 5 times more likely than the M dwarfs to harbor a giant
planet. Our analysis shows that the correlation between Jovian planet
occurrence and stellar mass remains even after accounting for the effects of
stellar metallicity.Comment: ApJ accepted, 27 pages, 6 figures, 3 table
UVSat: a concept of an ultraviolet/optical photometric satellite
Time-series photometry from space in the ultraviolet can be presently done
with only a few platforms, none of which is able to provide wide-field
long-term high-cadence photometry. We present a concept of UVSat, a twin space
telescope which will be capable to perform this kind of photometry, filling an
observational niche. The satellite will host two telescopes, one for
observations in the ultraviolet, the other for observations in the optical
band. We also briefly show what science can be done with UVSat.Comment: 6 pages, 2 figures, accepted for publication in the Proceedings of
the PAS (Proc. of the 2nd BRITE Science conference, Innsbruck
Precise radial velocities of giant stars. IV. A correlation between surface gravity and radial velocity variation and a statistical investigation of companion properties
Since 1999, we have been conducting a radial velocity survey of 179 K giants
using the CAT at UCO/Lick observatory. At present ~20-100 measurements have
been collected per star with a precision of 5 to 8 m/s. Of the stars monitored,
145 (80%) show radial velocity (RV) variations at a level >20 m/s, of which 43
exhibit significant periodicities. Our aim is to investigate possible
mechanism(s) that cause these observed RV variations. We intend to test whether
these variations are intrinsic in nature, or possibly induced by companions, or
both. In addition, we aim to characterise the parameters of these companions. A
relation between log g and the amplitude of the RV variations is investigated
for all stars in the sample. Furthermore, the hypothesis that all periodic RV
variations are caused by companions is investigated by comparing their inferred
orbital statistics with the statistics of companions around main sequence
stars. A strong relation is found between the amplitude of the RV variations
and log g in K giant stars, as suggested earlier by Hatzes & Cochran (1998).
However, most of the stars exhibiting periodic variations are located above
this relation. These RV variations can be split in a periodic component which
is not correlated with log g and a random residual part which does correlate
with log g. Compared to main-sequence stars, K giants frequently exhibit
periodic RV variations. Interpreting these RV variations as being caused by
companions, the orbital param eters are different from the companions orbiting
dwarfs. Intrinsic mechanisms play an important role in producing RV variations
in K giants stars, as suggested by their dependence on log g. However, it
appears that periodic RV variations are additional to these intrinsic
variations, consistent with them being caused by companions.Comment: 10 pages, accepted by A&
Constraints on a second planet in the WASP-3 system
There have been previous hints that the transiting planet WASP-3 b is
accompanied by a second planet in a nearby orbit, based on small deviations
from strict periodicity of the observed transits. Here we present 17 precise
radial velocity measurements and 32 transit light curves that were acquired
between 2009 and 2011. These data were used to refine the parameters of the
host star and transiting planet. This has resulted in reduced uncertainties for
the radii and masses of the star and planet. The radial-velocity data and the
transit times show no evidence for an additional planet in the system.
Therefore, we have determined the upper limit on the mass of any hypothetical
second planet, as a function of its orbital period.Comment: Accepted for publication in The Astronomical Journa
Extrasolar planets and brown dwarfs around A-F type stars VI. High precision RV survey of early type dwarfs with HARPS
(Abridged) Aims: Systematic surveys to search for exoplanets have been mostly
dedicated to solar-type stars sofar. We developed in 2004 a method to extend
such searches to earlier A-F type dwarfs and started spectroscopic surveys to
search for planets and quantify the detection limit achievable when taking into
account the stars properties and their actual levels of intrinsic variations.
We give here the first results of our southern survey with HARPS.
Results: 1) 64% of the 170 stars with enough data points are found to be
variable. 20 are found to be binaries or candidate binaries (with stars or
brown dwarfs). More than 80% or the latest type stars (once binaries are
removed) are intrinsically variable at a 2 m/s precision level. Stars with
earlier spectral type (B-V <= 0.2) are either variable or associated to levels
of uncertainties comparable to the RV rms observed on variable stars of same
B-V. 2) We have detected one long-period planetary system around an F6IV-V
star. 3) We have quantified the jitter due to stellar activity and we show that
taking into account this jitter in addition to the stellar parameters, it is
still possible to detect planets with HARPS with periods of 3 days (resp. 10
days and 100 days) on 91% (resp. 83%, 61%) of them. We show that even the
earliest spectral type stars are accessible to this type of search, provided
they have a low vsini and low levels of activity. 4) Taking into account the
present data, we compute the actually achieved detection limits for 107 targets
and discuss the limits as a function of B-V. Given the data at hand, our survey
is sensitive to short-period (few days) planets and to longer ones (100 days)
at a lower extent (latest type stars). We derive first constrains on the
presence of planets around A-F stars for these ranges of periods.Comment: 18 pages, 12 figures, 5 tables, A&A accepte
Cosmic ray neon, Wolf-Rayet stars, and the superbubble origin of galactic cosmic rays
The abundances of neon isotopes in the galactic cosmic rays (GCRs) are
reported using data from the Cosmic Ray Isotope Spectrometer (CRIS) aboard the
Advanced Composition Explorer (ACE). We compare our ACE-CRIS data for neon and
refractory isotope ratios, and data from other experiments, with recent results
from two-component Wolf-Rayet (WR) models. The three largest deviations of GCR
isotope ratios from solar-system ratios predicted by these models are indeed
present in the GCRs. Since WR stars are evolutionary products of OB stars, and
most OB stars exist in OB associations that form superbubbles, the good
agreement of these data with WR models suggests that superbubbles are the
likely source of at least a substantial fraction of GCRs.Comment: 22 pages, 6 figures Accepted for publication by Ap
Transit timing variation and activity in the WASP-10 planetary system
Transit timing analysis may be an effective method of discovering additional
bodies in extrasolar systems which harbour transiting exoplanets. The
deviations from the Keplerian motion, caused by mutual gravitational
interactions between planets, are expected to generate transit timing
variations of transiting exoplanets. In 2009 we collected 9 light curves of 8
transits of the exoplanet WASP-10b. Combining these data with published ones,
we found that transit timing cannot be explained by a constant period but by a
periodic variation. Simplified three-body models which reproduce the observed
variations of timing residuals were identified by numerical simulations. We
found that the configuration with an additional planet of mass of 0.1
and orbital period of 5.23 d, located close to the outer 5:3
mean motion resonance, is the most likely scenario. If the second planet is a
transiter, the estimated flux drop will be 0.3 per cent and can be
observable with a ground-based telescope. Moreover, we present evidence that
the spots on the stellar surface and rotation of the star affect the radial
velocity curve giving rise to spurious eccentricity of the orbit of the first
planet. We argue that the orbit of WASP-10b is essentially circular. Using the
gyrochronology method, the host star was found to be Myr old. This
young age can explain the large radius reported for WASP-10b.Comment: MNRAS accepte
The Mass of the Planet-hosting Giant Star Beta Geminorum Determined from its p-mode Oscillation Spectrum
We use precise radial velocity measurements and photometric data to derive
the frequency spacing of the p-mode oscillation spectrum of the planet-hosting
star Beta Gem. This spacing along with the interferometric radius for this star
is used to derive an accurate stellar mass. A long time series of over 60 hours
of precise stellar radial velocity measurements of Beta Gem were taken with an
iodine absorption cell and the echelle spectrograph mounted on the 2m Alfred
Jensch Telescope. Complementary photometric data for this star were also taken
with the MOST microsatellite spanning 3.6 d. A Fourier analysis of the radial
velocity data reveals the presence of up to 17 significant pulsation modes in
the frequency interval 10-250 micro-Hz. Most of these fall on a grid of
equally-spaced frequencies having a separation of 7.14 +/- 0.12 micro-Hz. An
analysis of 3.6 days of high precision photometry taken with the MOST space
telescope shows the presence of up to 16 modes, six of which are consistent
with modes found in the spectral (radial velocity) data. This frequency spacing
is consistent with high overtone radial pulsations; however, until the
pulsation modes are identified we cannot be sure if some of these are nonradial
modes or even mixed modes. The radial velocity frequency spacing along with
angular diameter measurements of Beta Gem via interferometry results in a
stellar mass of M = 1.91 +/- 0.09 solar masses. This value confirms the
intermediate mass of the star determined using stellar evolutionary tracks.
Beta Gem is confirmed to be an intermediate mass star. Stellar pulsations in
giant stars along with interferometric radius measurements can provide accurate
determinations of the stellar mass of planet hosting giant stars. These can
also be used to calibrate stellar evolutionary tracks.Comment: Accepted by Astronomy and Astrophysic
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