Publications (2)0 Total impact
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ABSTRACT: Precise stellar radial velocities are used to search for massive (Jupiter
masses or higher) exoplanets around the stars of the open cluster M67. We aim
to obtain a census of massive exoplanets in a cluster of solar metallicity and
age in order to study the dependence of planet formation on stellar mass and to
compare in detail the chemical composition of stars with and without planets.
This first work presents the sample and the observations, discusses the cluster
characteristics and the radial velocity (RV) distribution of the stars, and
individuates the most likely planetary host candidates. We observed a total of
88 main-sequence stars, subgiants, and giants all highly probable members of
M67, using four telescopes and instrument combinations. We investigate whether
exoplanets are present by obtaining radial velocities with precisions as good
as 10 m/s. To date, we have performed 680 single observations (Dec. 2011) and a
preliminary analysis of data, spanning a period of up to eight years. Although
the sample was pre-selected to avoid the inclusion of binaries, we identify 11
previously unknown binary candidates. Eleven stars clearly displayed larger RV
variability and these are candidates to host long-term substellar companions.
The average RV is also independent of the stellar magnitude and evolutionary
status, confirming that the difference in gravitational redshift between giants
and dwarfs is almost cancelled by the atmospheric motions. We use the subsample
of solar-type stars to derive a precise true RV for this cluster. We finally
create a catalog of binaries and use it to clean the color magnitude diagram
(CMD). As conclusion, by pushing the search for planets to the faintest
possible magnitudes, it is possible to observe solar analogues in open
clusters, and we propose 11 candidates to host substellar companions.
06/2012;
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J. L. Birkby,
S. V. Nefs,
S. T. Hodgkin,
G. Kovács,
B. Sipöcz,
D. J. Pinfield,
I. A. G. Snellen,
D. Mislis,
F. Murgas,
N. Lodieu,
E. J. W. de Mooij,
N. Goulding,
P. Cruz,
H. Stoev,
M. Cappetta,
E. Pallé,
D. Barrado, R. Saglia,
E. L. Martín,
Y. Pavlenko
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ABSTRACT: We report the discovery of 16 detached M-dwarf eclipsing binaries with J<16
mag and provide a detailed characterisation of three of them, using
high-precision infrared light curves from the WFCAM Transit Survey (WTS). Such
systems provide the most accurate and model-independent method for measuring
the fundamental parameters of these poorly understood yet numerous stars, which
currently lack sufficient observations to precisely calibrate stellar evolution
models. We fully solve for the masses and radii of three of the systems,
finding orbital periods in the range 1.5<P<4.9 days, with masses spanning
0.35-0.50 Msun and radii between 0.38-0.50 Rsun, with uncertainties of
~3.5-6.4% in mass and ~2.7-5.5% in radius. Close-companions in short-period
binaries are expected to be tidally-locked into fast rotational velocities,
resulting in high levels of magnetic activity. This is predicted to inflate
their radii by inhibiting convective flow and increasing star spot coverage.
The radii of the WTS systems are inflated above model predictions by ~3-12%, in
agreement with the observed trend, despite an expected lower systematic
contribution from star spots signals at infrared wavelengths. We searched for
correlation between the orbital period and radius inflation by combining our
results with all existing M-dwarf radius measurements of comparable precision,
but we found no statistically significant evidence for a decrease in radius
inflation for longer period, less active systems. Radius inflation continues to
exists in non-synchronised systems indicating that the problem remains even for
very low activity M-dwarfs. Resolving this issue is vital not only for
understanding the most populous stars in the Universe, but also for
characterising their planetary companions, which hold the best prospects for
finding Earth-like planets in the traditional habitable zone.
06/2012;
