1,548 research outputs found
TRAPPIST: a robotic telescope dedicated to the study of planetary systems
We present here a new robotic telescope called TRAPPIST (TRAnsiting Planets
and PlanetesImals Small Telescope). Equipped with a high-quality CCD camera
mounted on a 0.6 meter light weight optical tube, TRAPPIST has been installed
in April 2010 at the ESO La Silla Observatory (Chile), and is now beginning its
scientific program. The science goal of TRAPPIST is the study of planetary
systems through two approaches: the detection and study of exoplanets, and the
study of comets. We describe here the objectives of the project, the hardware,
and we present some of the first results obtained during the commissioning
phase.Comment: To appear in Detection and Dynamics of Transiting Exoplanets,
Proceedings of Haute Provence Observatory Colloquium (23-27 August 2010),
eds. F. Bouchy, R.F. Diaz & C.Moutou, Platypus press 201
The CORALIE survey for southern extra-solar planets. X. A Hot Jupiter orbiting HD73256
Recent radial-velocity measurements obtained with the CORALIE spectrograph on
the 1.2-m Euler Swiss telescope at La Silla unveil the presence of a new
Jovian-mass Hot Jupiter around HD 73256. The 1.85-M_Jup planet moves on an
extremely short-period (P=2.5486 d), quasi-circular orbit. The best Keplerian
orbital solution is presented together with an unsuccessful photometric
planetary-transit search performed with the SAT Danish telescope at La Silla.
Over the time span of the observations, the photometric follow-up of the
candidate has nevertheless revealed a P=14-d photometric periodicity
corresponding to the rotational period of the star. This variation as well as
the radial-velocity jitter around the Keplerian solution are shown to be
related to the fair activity level known for HD 73256.Comment: 7 pages, 7 figures. Accepted in A&
Do we expect to find the Super-Earths close to the gas giants?
We have investigated the evolution of a pair of interacting planets embedded
in a gaseous disc, considering the possibility of the resonant capture of a
Super-Earth by a Jupiter mass gas giant. First, we have examined the situation
where the Super-Earth is on the internal orbit and the gas giant on the
external one. It has been found that the terrestrial planet is scattered from
the disc or the gas giant captures the Super-Earth into an interior 3:2 or 4:3
mean-motion resonance. The stability of the latter configurations depends on
the initial planet positions and on eccentricity evolution. The behaviour of
the system is different if the Super-Earth is the external planet. We have
found that instead of being captured in the mean-motion resonance, the
terrestrial planet is trapped at the outer edge of the gap opened by the gas
giant. This effect prevents the occurrence of the first order mean-motion
commensurability. These results are particularly interesting in light of recent
exoplanet discoveries and provide predictions of what will become
observationally testable in the near future.Comment: 7 pages, to appear in the proceedings of the conference "Extra-solar
Planets in Multi-body Systems: Theory and Observations"; eds. K. Gozdziewski,
A. Niedzielski and J. Schneider, EAS Publication Serie
Astrometric planet search around southern ultracool dwarfs III. Discovery of a brown dwarf in a 3-year orbit around DE0630-18
Using astrometric measurements obtained with the FORS2/VLT camera, we are
searching for low-mass companions around 20 nearby ultracool dwarfs. With a
single-measurement precision of 0.1 milli-arcseconds, our survey is sensitive
to a wide range of companion masses from planetary companions to binary
systems. Here, we report the discovery and orbit characterisation of a new
ultracool binary at a distance of 19.5 pc from Earth that is composed of the
M8.5-dwarf primary DE0630-18 and a substellar companion. The nearly edge-on
orbit is moderately eccentric (e=0.23) with an orbital period of 1120 d, which
corresponds to a relative separation in semimajor axis of approximately 1.1 AU.
We obtained a high-resolution optical spectrum with UVES/VLT and measured the
system's heliocentric radial velocity. The spectrum does not exhibit lithium
absorption at 670.8 nm, indicating that the system is not extremely young. A
preliminary estimate of the binary's physical parameters tells us that it is
composed of a primary at the stellar-substellar limit and a massive brown-dwarf
companion. DE0630-18 is a new very low-mass binary system with a
well-characterised orbit.Comment: 4 pages, 7 figures. Accepted for publication in A&
Astrometric planet search around southern ultracool dwarfs II: Astrometric reduction methods and a deep astrometric catalogue
We describe the astrometric reduction of images obtained with the FORS2/VLT
camera in the framework of an astrometric planet search around 20
M/L-transition dwarfs. We present the correction of systematic errors, the
achieved astrometric performance, and a new astrometric catalogue containing
the faint reference stars in 20 fields located close to the Galactic plane. We
detected three types of systematic errors in the FORS2 astrometry: the relative
motion of the camera's two CCD chips, errors that are correlated in space, and
an error contribution of yet unexplained origin. The relative CCD motion has
probably a thermal origin and usually is 0.001-0.010 px (~0.1-1 mas), but
sometimes amounts to 0.02-0.05 px (3-6 mas). This instability and
space-correlated errors are detected and mitigated using reference stars. The
third component of unknown origin has an amplitude of 0.03-0.14 mas and is
independent of the observing conditions. We find that a consecutive sequence of
32 images of a well-exposed star over 40 min at 0.6" seeing results in a median
r.m.s. of the epoch residuals of 0.126 mas. Overall, the epoch residuals are
distributed according to a normal law with a chi2~1. We compiled a catalogue of
12000 stars with I-band magnitudes of 16-22 located in 20 fields, each covering
~2x2'. It contains I-band magnitudes, ICRF positions with 40-70 mas precision,
and relative proper motions and absolute trigonometric parallaxes with a
precision of 0.1 mas/yr and 0.1 mas at the bright end, respectively.Comment: 17 pages, 19 figures, 4 tables, accepted for publication in A&A on
March 14, 201
Astrometric planet search around southern ultracool dwarfs I: First results, including parallaxes of 20 M8-L2 dwarfs
Extrasolar planet searches targeting very low-mass stars and brown dwarfs are
hampered by intrinsic or instrumental limitations. Time series of astrometric
measurements with precisions better than one milli-arcsecond can yield new
evidence on the planet occurrence around these objects. We present first
results of an astrometric search for planets around 20 nearby dwarf stars with
spectral types M8-L2. Over a timespan of two years, we obtained I-band images
of the target fields with the FORS2 camera at the Very Large Telescope. Using
background stars as references, we monitored the targets' astrometric
trajectories, which allowed us to measure parallax and proper motions, set
limits on the presence of planets, and to discover the orbital motions of two
binary systems. We determined trigonometric parallaxes with an average accuracy
of 0.09 mas (~0.2 %) resulting in a reference sample for the study of ultracool
dwarfs at the M/L transition, whose members are located at distances of 9.5-40
pc. This sample contains two newly discovered tight binaries (DE0630-18 and
DE0823-49) and one previously known wide binary (DE1520-44). Only one target
shows I-band variability >5 mmag r.m.s. We derived planet exclusion limits that
set an upper limit of 9 % to the occurrence of giant planets with masses >5
MJup in intermediate-separation (0.01-0.8 AU) orbits around M8-L2 dwarfs. We
demonstrated that astrometric observations with an accuracy of 120 micro-arcsec
over two years are feasible from the ground and can be used for a planet search
survey. The detection of two tight very low-mass binaries showed that our
search strategy is efficient and may lead to the detection of planetary-mass
companions through follow-up observations.Comment: 19 pages. Accepted to A&A on March 10, 2014. This is the accepted
version of the paper that includes minor changes and language editin
Astrometric orbit of a low-mass companion to an ultracool dwarf
Little is known about the existence of extrasolar planets around ultracool
dwarfs. Furthermore, binary stars with Sun-like primaries and very low-mass
binaries composed of ultracool dwarfs show differences in the distributions of
mass ratio and orbital separation that can be indicative of distinct formation
mechanisms. Using FORS2/VLT optical imaging for high precision astrometry we
are searching for planets and substellar objects around ultracool dwarfs to
investigate their multiplicity properties for very low companion masses. Here
we report astrometric measurements with an accuracy of two tenths of a
milli-arcsecond over two years that reveal orbital motion of the nearby L1.5
dwarf DENIS-P J082303.1-491201 located at 20.77 +/- 0.08 pc caused by an unseen
companion that revolves about its host on an eccentric orbit in 246.4 +/- 1.4
days. We estimate the L1.5 dwarf to have 7.5 +/- 0.7 % of the Sun's mass that
implies a companion mass of 28 +/- 2 Jupiter masses. This new system has the
smallest mass ratio (0.36 +/- 0.02) of known very low-mass binaries with
characterised orbits. With this discovery we demonstrate 200 micro-arcsecond
astrometry over an arc-minute field and over several years that is sufficient
to discover sub-Jupiter mass planets around ultracool dwarfs. We also show that
the achieved parallax accuracy of < 0.4 % makes it possible to remove distance
as a dominant source of uncertainty in the modelling of ultracool dwarfs.Comment: 9 pages, 8 figures, accepted for publication in Astronomy and
Astrophysics. The reduced astrometry data will be made publically available
through the CD
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