In this paper, we report a refined determination of the orbital parameters and the detection of the Rossiter-McLaughlin effect of the recently discovered transiting exoplanet HD147506b (HAT-P-2b). ...The large orbital eccentricity at the short orbital period of this exoplanet is unexpected and is distinguishing from other known transiting exoplanets. We performed high-precision radial velocity spectroscopic observations of HD147506 (HAT-P-2) with the new spectrograph SOPHIE, mounted on the 1.93 m telescope at the Haute-Provence observatory (OHP). We obtained 63 new measurements, including 35 on May 14 and 20 on June 11, when the planet was transiting its parent star. The radial velocity (RV) anomaly observed illustrates that HAT-P-2b orbital motion is set in the same direction as its parent star spin. The sky-projected angle between the normal of the orbital plane and the stellar spin axis, \lambda = 0.2 +12.2 -12.5 deg, is consistent with zero. The planetary and stellar radii were re-determined, yielding R_p = 0.951 +0.039 -0.053 R_Jup, R_s = 1.416 +0.040 -0.062 R_Sun. The mass M_p = 8.62 +0.39 -0.55 M_Jup and radius of HAT-P-2b indicate a density of 12.5 +2.6 -3.6 g cm^{-3}, suggesting an object in between the known close-in planets with typical density of the order of 1 g cm^{-3}, and the very low-mass stars, with density greater than 50 g cm^{-3}.
We investigate the mass function in the substellar domain down to a few Jupiter masses in the young sigma Orionis open cluster (3+/-2 Ma, d = 360^+70_-60 pc). We have performed a deep IJ-band search, ...covering an area of 790 arcmin^2 close to the cluster centre. This survey was complemented with an infrared follow-up in the HKs- and Spitzer 3.6-8.0 mum-bands. Using colour-magnitude diagrams, we have selected 49 candidate cluster members in the magnitude interval 16.1 mag < I < 23.0 mag. Accounting for flux excesses at 8.0 mum and previously known spectral features of youth, 30 objects are bona fide cluster members. Four are first identified from our optical-near infrared data. Eleven have most probable masses below the deuterium burning limit and are classified as planetary-mass object candidates. The slope of the substellar mass spectrum (Delta N / Delta M = a M^-alpha) in the mass interval 0.11 Msol M < 0.006 Msol is alpha = +0.6+/-0.2. Any opacity mass-limit, if these objects form via fragmentation, may lie below 0.006 Msol. The frequency of sigma Orionis brown dwarfs with circumsubstellar discs is 47+/-15 %. The continuity in the mass function and in the frequency of discs suggests that very low-mass stars and substellar objects, even below the deuterium-burning mass limit, may share the same formation mechanism.
We have obtained adaptive optics images and accurate radial velocities for 7
very low mass systems, in the course of a long term effort to determine
accurate masses for very low mass stars (M<0.6 ...Solar Mass). We use the new
data, together with measurements from the litterature for some stars, to
determine new or improved orbits for these 7 systems. They provide masses for
16 very low mass stars with accuracies that range between 0.2% and 5%, and in
some cases a very accurate distance as well. This information is used in a
companion paper to discuss the Mass-Luminosity relation for the V, J, H and K
photometric bands.
We present improved visual and near-infrared empirical mass-luminosity
relations for very low mass stars (M$<$0.6~\Msol). These relations make use of
all stellar masses in this range known with ...better than 10% accuracy, most of
which are new determinations with 0.2 to 5% accuracy from our own programme,
presented in a companion paper.
As predicted by stellar structure models, the metallicity dispersion of the
field populations induces a large scatter around the mean V band relation,
while the infrared relations are much tighter. The agreement of the observed
infrared mass-luminosity relations with the theoretical relations of Baraffe et
al. (1998) and Siess et al. (2000) is impressive, while we find an increasingly
significant discrepancy in the V band for decreasing masses. The theoretical
mass-luminosity relation which is insufficiently steep, and has introduced some
errors in the local stellar mass functions derived from V band luminosity
functions.
We report here the discovery of two planet candidates as a result of our planet-search programme biased in favour of high-metallicity stars, using the ELODIE spectrograph at the Observatoire de Haute ...Provence. One of them has a minimum mass m_2\sin{i} = 2.5 M_Jup and is orbiting the metal-rich star HD43691 with period P = 40 days and eccentricity e = 0.14. The other planet has a minimum mass m_2\sin{i} = 5.6 M_Jup and orbits the slightly metal-rich star HD132406 with period P = 974 days and eccentricity e = 0.34. Both stars were followed up with additional observations using the new SOPHIE spectrograph that replaces the ELODIE instrument, allowing an improved orbital solution for the systems.
Main Sequence (MS) stars are by far the most numerous class in the Universe.
They are often somewhat neglected as they are relatively quiet objects (but
exceptions exist), though they bear testimony ...of the past and future of our
Sun. An important characteristic of the MS stars, particularly the solar-type
ones, is that they host the large majority of the known extrasolar planets.
Moreover, at the bottom of the MS, the red M dwarfs pave the way to
understanding the physics of brown dwarfs and giant planets. We have measured
very precise angular diameters from recent VINCI/VLTI interferometric
observations of a number of MS stars in the K band, with spectral types between
A1V and M5.5V. They already cover a wide range of effective temperatures and
radii. Combined with precise Hipparcos parallaxes, photometry, spectroscopy as
well as the asteroseismic information available for some of these stars, the
angular diameters put strong constraints on the detailed models of these stars,
and therefore on the physical processes at play.
We present the discovery of a tight M8V binary, with a separation of only 1.2
astronomical units, obtained with the PUEO and NACO adaptive optics systems,
respectively at the CFHT and VLT telescopes. ...The estimated period of LP 349-25
is approximately 5 years, and this makes it an excellent candidate for a
precise mass measurement.
We present 30 new nearby (d<30 pc) red dwarf candidates, with estimated
spectral types M6 to M8. 26 were directly selected from the DENIS database, and
another 4 were first extracted from the LHS ...catalogue and cross-identified with
a DENIS counterpart. Their proper motions were measured on the MAMA measuring
machine from plates spanning 13 to 48 years, and are larger than 0.1 arcsec/yr,
ruling out the possibility that they are giants. Their distances were estimated
from the DENIS colours and IR colour-magnitude relations and range between 15
and 30 pc.
Context: L-type ultra-cool dwarfs and brown dwarfs have cloudy atmospheres that could host weather-like phenomena. The detection of photometric or spectral variability would provide insight into ...unresolved atmospheric heterogeneities, such as holes in a global cloud deck. Aims: It has been proposed that growth of heterogeneities in the global cloud deck may account for the L- to T-type transition as brown dwarf photospheres evolve from cloudy to clear conditions. Such a mechanism is compatible with variability. We searched for variability in the spectra of five L6 to T6 brown dwarfs in order to test this hypothesis. Methods: We obtained spectroscopic time series using VLT/ISAAC, over 0.99-1.13um, and IRTF/SpeX for two of our targets, in J, H and K bands. We search for statistically variable lines and correlation between those. Results: High spectral-frequency variations are seen in some objects, but these detections are marginal and need to be confirmed. We find no evidence for large amplitude variations in spectral morphology and we place firm upper limits of 2 to 3% on broad-band variability, on the time scale of a few hours. The T2 transition brown dwarf SDSS J1254-0122 shows numerous variable features, but a secure variability diagnosis would require further observations. Conclusions: Assuming that any variability arises from the rotation of patterns of large-scale clear and cloudy regions across the surface, we find that the typical physical scale of cloud cover disruption should be smaller than 5-8% of the disk area for four of our targets. The possible variations seen in SDSS J1254-0122 are not strong enough to allow us to confirm the cloud breaking hypothesis.
We present very accurate orbital parameters and mass measurements (2.4%
accuracy) for the well known very low mass triple system Gl 866. We obtain
first orbital elements for the short-period orbit ...and greatly improve the long
period orbit. All three stars have masses close to 0.1 solar masses, and the
system thus provides the strongest constraints to date on the mass-luminosity
relation close to the brown dwarf limit.
