HD3651B: the first directly imaged brown dwarf companion of an exoplanet host star

In the course of our ongoing multiplicity study of exoplanet host stars we detected a faint companion located at ~43arcsec (480AU physical projected separation) north-west of its primary -- the exoplanet host star HD3651 at 11pc. The companion, HD3651B, clearly shares the proper motion of the exoplanet host star in our four images, obtained with ESO/NTT and UKIRT, spanning three years in epoch difference. The magnitude of the companion is H=16.75+-0.16mag, the faintest co-moving companion of an exoplanet host star imaged directly. HD3651B is not detected in the POSS-II B-, R- and I-band images, indicating that this object is fainter than ~20mag in the B- and R-band and fainter than \~19mag in the I-band. With the Hipparcos distance of HD3651 of 11pc, the absolute magnitude of HD3651B is about 16.5mag in the H band. Our H-band photometry and the Baraffe et al. (2003) evolutionary models yield a mass of HD3651B to be 20 to 60MJup for assumed ages between 1 and 10Gyr. The effective temperature ranges between 800 and 900K, consistent with a spectral type of T7 to T8. We conclude that HD3651B is a brown-dwarf companion, the first of its kind directly imaged as a companion of an exoplanet host star, and one of the faintest T dwarfs found in the solar vicinity (within 11pc).Comment: 5 pages, 3 figures, 2 tables, accepted for publication in MNRAS LETTER

The High Eccentricity of the Planet Around 16 Cyg B

We consider the high eccentricity, 0.66, of the newly discovered planet around 16 Cyg B, using the fact that the parent star is part of a wide binary. We show that the high eccentricity of the planet could be the result of tidal forces exerted on 16 Cyg B and its planet by 16 Cyg A, the distant companion in the system. By following stellar triple systems with parameters similar to those of 16 Cyg, we have established that the orbital eccentricity of the planet could have gone through strong modulation, with an amplitude of 0.8 or even larger, with typical timescale of tens of millions years. The amplitude of the planet eccentricity strongly depends on the relative inclination between the plane of motion of the planet and that of the wide binary 16 Cyg AB. To account for the present eccentricity of the planet we have to assume that the angle between the two planes of motion is large, at least 60 deg. We argue that this assumption is reasonable for wide binaries like 16 Cyg AB.Comment: 2 Figures, Latex, submitted for publication to ApJ

A low-mass stellar companion of the planet host star HD75289

We report on the detection of a new low-mass stellar companion of HD75289, a G0V star that harbors one known radial-velocity planet (Udry et al. 2000). Comparing an image of 2MASS with an image we obtained with SofI at the ESO 3.58m NTT three years later, we detected a co-moving companion located 21.465+-0.023arcsecs (621+-10AU at 29pc) east of HD75289. A second SofI image taken 10 months later confirmed the common proper motion of HD75289B with its host star. The infrared spectrum and colors of the companion are consistent with an M2 to M5 main-sequence star at the distance of HD75289. No further (sub)stellar companion down to H = 19mag could be detected. With the SofI detection limit we can rule out additional stellar companions beyond 140AU and substellar companions with masses m > 0.050Msun from 400AU up to 2000AU.Comment: accepted in A&

Detection of the ellipsoidal and the relativistic beaming effects in the CoRoT-3 lightcurve

CoRoT-3b is a 22 Jupiter-mass massive-planet/brown-dwarf object, orbiting an F3-star with a period of 4.3 days. We analyzed the out-of-transit CoRoT-3 red-channel lightcurve obtained by the CoRoT mission and detected the ellipsoidal modulation, with half the orbital period and amplitude of 59+/-9 ppm (parts per million) and the relativistic beaming effect, with the orbital period and an amplitude of 27+/-9 ppm. Phases and amplitudes of both modulations were consistent with our theoretical approximation.Comment: Published in Astronomy & Astrophysics. 5 pages, 2 figure

The Smallest Mass Ratio Young Star Spectroscopic Binaries

Using high resolution near-infrared spectroscopy with the Keck telescope, we have detected the radial velocity signatures of the cool secondary components in four optically identified pre-main-sequence, single-lined spectroscopic binaries. All are weak-lined T Tauri stars with well-defined center of mass velocities. The mass ratio for one young binary, NTTS 160905-1859, is M2/M1 = 0.18+/-0.01, the smallest yet measured dynamically for a pre-main-sequence spectroscopic binary. These new results demonstrate the power of infrared spectroscopy for the dynamical identification of cool secondaries. Visible light spectroscopy, to date, has not revealed any pre-main-sequence secondary stars with masses <0.5 M_sun, while two of the young systems reported here are in that range. We compare our targets with a compilation of the published young double-lined spectroscopic binaries and discuss our unique contribution to this sample.Comment: Accepted for publication in the April, 2002, ApJ; 6 figure

Correcting systematic effects in a large set of photometric light curves

We suggest a new algorithm to remove systematic effects in a large set of light curves obtained by a photometric survey. The algorithm can remove systematic effects, such as those associated with atmospheric extinction, detector efficiency, or point spread function changes over the detector. The algorithm works without any prior knowledge of the effects, as long as they linearly appear in many stars of the sample. The approach, which was originally developed to remove atmospheric extinction effects, is based on a lower rank approximation of matrices, an approach which has already been suggested and used in chemometrics, for example. The proposed algorithm is especially useful in cases where the uncertainties of the measurements are unequal. For equal uncertainties, the algorithm reduces to the Principal Component Analysis (PCA) algorithm. We present a simulation to demonstrate the effectiveness of the proposed algorithm and we point out its potential, in the search for transit candidates in particula