J.-P. Sivan

No planet for HD 166435

The G0 V star HD 166435 has been observed by the ber-fed spectrograph ELODIE as one of the targets in the large extra-solar planet survey that we are conducting at the Observatory of Haute-Provence. We detected coherent, low-amplitude, radial-velocity variations with a period of 3.7987 days, suggesting a possible close-in planetary companion. Subsequently, we initiated a series of high-precision photometric observations to search for possible planetary transits and an additional series of Ca II H and K observations to measure the level of surface magnetic activity and to look for possible rotational modulation. Surprisingly, we found the star to be photometrically variable and magnetically active. A detailed study of the phase stability of the radial-velocity signal revealed that the radial-velocity variability remains coherent only for durations of about 30 days. Analysis of the time variation of the spectroscopic line proles using line bisectors revealed a correlation between radial velocity and line-bisector orientation. All of these observations, along with a one-quarter cycle phase shift between the photometric and the radial-velocity variations, are well explained by the presence of dark photospheric spots on HD 166435. We conclude that the radial-velocity variations are not due to gravitational interaction with an orbiting planet but, instead, originate from line-prole changes stemming from star spots on the surface of the star. The quasi-coherence of the radial-velocity signal over more than two years, which allowed a fair t with a binary model, makes the stability of this star unusual among other active stars. It suggests a stable magnetic eld orientation where spots are always generated at about the same location on the surface of the star.

An extrasolar planetary system with three Neptune-mass planets

Over the past two years, the search for low-mass extrasolar planets has led to the detection of seven so-called ‘hot Neptunes’ or ‘super-Earths’ around Sun-like stars. These planets have masses 5–20 times larger than the Earth and are mainly found on close-in orbits with periods of 2–15 days. Here we report a system of three Neptune-mass planets with periods of 8.67, 31.6 and 197 days, orbiting the nearby star HD 69830. This star was already known to show an infrared excess possibly caused by an asteroid belt within 1 au (the Sun–Earth distance). Simulations show that the system is in a dynamically stable configuration. Theoretical calculations favour a mainly rocky composition for both inner planets, while the outer planet probably has a significant gaseous envelope surrounding its rocky/icy core; the outer planet orbits within the habitable zone of this star.

The Spectroscopic Orbit of the Planetary Companion Transiting HD 209458

We report a spectroscopic orbit with period P=3.52433+/-0.00027 days for the planetary companion that transits the solar-type star HD 209458. For the metallicity, mass, and radius of the star, we derive [Fe/H&sqbr0;=0.00+/-0.02, M*=1.1+/-0.1 M middle dot in circle, and R*=1.2+/-0.1 R middle dot in circle. This is based on a new analysis of the iron lines in our HIRES template spectrum and also on the absolute magnitude, effective temperature, and color of the star, and it uses isochrones from four different sets of stellar evolution models. Using these values for the stellar parameters, we reanalyze the transit data and derive an orbital inclination of i=86&fdg;1+/-1&fdg;6. For the planet, we derive a mass of Mp=0.69+/-0.05 MJup, a radius of Rp=1.40+/-0.17 RJup, and a density of rho=0.31+/-0.07 g cm-3.

HD 80606 b, a planet on an extremely elongated orbit ?

We report the detection of a planetary companion orbiting the solar-type star HD 80606, the brighter component of a wide binary with a projected separation of about 2000 AU. Using high-signal spectroscopic observations of the two components of the visual binary, we show that they are nearly identical. The planet has an orbital period of 111.8 days and a minimum mass of 3:9MJup .W ithe = 0.927, this planet has the highest orbital eccentricity among the extrasolar planets detected so far. We nally list several processes this extreme eccentricity could result from.

The HARPS search for southern extra-solar planets ⋆ V . A 14 Earth-masses planet orbiting HD 4308

We present here the discovery and characterisation of a very light planet around HD4308. The planet orbits its star in 15.56 days. The circular radial-velocity variation presents a tiny semi-amplitude of 4.1 m/s that corresponds to a planetary minimum mass m2sin(i)=14.1 Earth masses. The planet was unveiled by high-precision radial-velocity measurements obtained with the HARPS spectrograph on the ESO 3.6-m telescope. The radial-velocity residuals around the Keplerian solution are 1.3 m/s, demonstrating the very high quality of the HARPS measurements. Activity and bisector indicators exclude any significant perturbations of stellar intrinsic origin, which supports the planetary interpretation. Contrary to most planet-host stars, HD4308 has a marked sub-solar metallicity ([Fe/H]=-0.31), raising the possibility that very light planet occurrence might show a different coupling with the parent star\s metallicity than do giant gaseous extra-solar planets. Together with Neptune-mass planets close to their parent stars, the new planet occupies a position in the mass-separation parameter space that is constraining for planet-formation and evolution theories. The question of whether they can be considered as residuals of evaporated gaseous giant planets, ice giants, or super-earth planets is discussed in the context of the latest core-accretion models.

The HARPS search for southern extra-solar planets. VIII.

Context. The µ Arae planetary system is fairly complex, because it contains two already known planets, µ Arae b with P = 640 days and µ Arae c with P = 9.64 days , and a third companion on a wide, but still poorly defined, orbit. Aims. Even with three planets in the system, the data points keep anomalously high dispersion around the fitted solution. The high residuals are only partially due to the strong p-mode oscillations of the host star. We therefore studied the possible presence of a fourth planet in this system. Methods. During the past years we carried out additional and extremely precise radial-velocity measurements with the HARPS spectrograph. These data turned out to be highly important for constraining the many free parameters in a four-planet orbital fit. Nevertheless, the search for the best solution remains difficult in this complex and multi-dimensional parameter space. The new Stakanof software, that uses an optimized genetic algorithm, helped us considerably in this task and made our search extremely efficient and successful. Results. We provide a full orbital solution of the planetary system around µ Arae. It turns out to be the second system known to harbor 4 planetary companions. Before this study, µ Arae b was already well known and characterized. Thanks to the new data points acquired with HARPS we can confirm the presence of µ Arae c at P = 9.64 days, which produces a coherent RV signal over more than two years. The new orbital fit sets the mass of µ Arae c to 10.5 M⊕. Furthermore, we present the discovery of µ Arae d, a new planet on an almost circular 310 day-period and with a mass of 0.52 MJup. Finally, we give completely new orbital parameters for the longest-period planet, µ Arae e. It is the first time that this companion has been constrained by radial-velocity data into a dynamical stable orbit, which leaves no doubt about its planetary nature. We take this opportunity to discuss naming conventions for poorly characterized planets.

\mu

We present our ELODIE radial-velocity measurements of HD 74156 and 14 Her (HD 145675). These stars ex- hibit low-amplitude radial-velocity variations induced by the presence of low-mass companions. The radial-velocity data of HD 74156 reveal the presence of two planetary companions: a 1.86 MJup planet on a 51.64-d orbit and a 6.2 MJup planet on a long-period (� 5.5 yr) orbit. Both orbits are fairly eccentric (e = 0.64 and 0.58). The 4.7 MJup companion to 14 Her has a long period (4.9 yr) and a moderately eccentric orbit (e = 0.34). We detect an additional linear radial-velocity trend superimposed on the periodic signal for this star. We also compute updated orbital solutions for HD 209458 and 51 Peg (HD 217014). Finally, we present our ELODIE radial-velocity data and orbital solutions for 5 stars known to host planetary companions: Ups And (HD 9826), 55 Cnc (HD 75732), 47 UMa (HD 95128), 70 Vir (HD 117176) and HD 187123. We confirm the previously pub- lished orbital solutions for Ups And, 70 Vir and HD 187123. Our data are not sufficient to fully confirm the orbital solutions for 55 Cnc and 47 UMa.

Arae , a system with four planets

HARPS is a high-resolution spectrograph dedicated to the search for extra-solar planets by means of precise radial- velocity measurements. It will be installed on the ESO 3.6-m telescope at the ESO La Silla observatory and should start its operation son end 2002. The observations will provides for many solar-type stars of the solar vicinity a high number of RV measurements with 1 ms-1 accuracy and will allow the detection of Saturn-like planets. The instrument is a fiber-fed and cross-dispersed echelle spectrograph. It has been designed and optimized to measure the Doppler shift of the stellar spectrum by means of cross correction of the spectrum with a numerical mask. For this purpose the entire spectrum in the wavelength range from 380 nm to 680 nm is imaged on a 4k4 mosaic CCD detector at a spectral resolution of about R equals 90,000. Wavelength calibration is provided by a ThAr lamp simultaneously imaged on the CCD. The HARPS spectrograph is also characterized by its high optical efficiency and the high thermo-mechanical stability. Indeed the whole instrument will be temperature controlled and operated in vacuum, in order to assure its short and long-term stability. This paper summarizes the present status of the project and describes the optical and instrument design of HARPS. Also a short presentation of the scientific objectives pursued with HARPS is given by the author.

The ELODIE survey for northern extra-solar planets - III. Three planetary candidates detected with ELODIE

We report the presence of a planet orbiting HD196885_A, with an orbital period of 1349 days. This star was previously suggested to host a 386-day planet, but we cannot confirm its existence. We also detect the presence of a stellar companion, HD196885_B, and give some constraints on its orbit.

HARPS: a new high-resolution spectrograph for the search of extrasolar planets

Precise radial-velocity observations at Haute-Provence Observatory (OHP, France) with the ELODIE echelle spectrograph have been undertaken since 1994. In addition to several discoveries described elsewhere, including and following that of 51 Peg b, they reveal new sub-stellar companions with essentially moderate to long periods. We report here about such companions orbiting five solar-type stars (HD 8574, HD 23596, HD 33636, HD 50554, HD 106252) and one sub-giant star (HD 190228). The companion of HD 8574 has an intermediate period of 227.55 days and a semi-major axis of 0.77 AU. All other companions have long periods, exceeding 3 years, and consequently their semi-major axes are around or above 2 AU. The detected companions have minimum masses