arXiv subjects

M. Mayor

Publications and source records attributed to M. Mayor.

270 records · Page 15Linked to original sources

arXiv2001

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 3.9 M_Jup. With e=0.927, this planet has the highest orbital eccentricity among the extrasolar planets detected so far. We finally list several processes this extreme eccentricity could result from.

astro-ph↗

arXiv2001

Driving current through single organic molecules

We investigate electronic transport through two types of conjugated molecules. Mechanically controlled break-junctions are used to couple thiol endgroups of single molecules to two gold electrodes. Current-voltage characteristics (IVs) of the metal-molecule-metal system are observed. These IVs reproduce the spatial symmetry of the molecules with respect to the direction of current flow. We hereby unambigously detect an intrinsic property of the molecule, and are able to distinguish the influence of both the molecule and the contact to the metal electrodes on the transport properties of the compound system.

cond-mat.mes-hall↗

arXiv2001

The metal-rich nature of stars with planets

With the goal of confirming the metallicity "excess" present in stars with planetary-mass companions, we present in this paper a high-precision spectroscopic study of a sample of dwarfs included in the CORALIE extrasolar planet survey. The targets were chosen according to the basic criteria that 1) they formed part of a limited volume and 2) they did not present the signature of a planetary host companion. A few stars with planets were also observed and analysed; namely, HD 6434, HD 13445, HD 16141, HD 17051, HD 19994, HD 22049, HD 28185, HD 38529, HD 52265, HD 190228, HD 210277 and HD 217107. For some of these objects there had been no previous spectroscopic studies. The spectroscopic analysis was done using the same technique as in previous work on the metallicity of stars with planets, thereby permitting a direct comparison of the results. The work described in this paper thus represents the first uniform and unbiased comparison between stars with and without planetary-mass companions in a volume-limited sample. The results show that 1) stars with planets are significantly metal-rich, and 2) that the source of the metallicity is most probably "primordial". The results presented here may impose serious constraints on planetary system formation and evolution models.

astro-ph↗

arXiv2001

Bisector analysis as a diagnostic of intrinsic radial-velocity variations

In this contribution we present the results of the application of the bisector of the cross-correlation function as a diagnostic of activity-related radial-velocity variations. The results show that the technique is very effective. We present examples for which the application of the bisector analysis was essential to establish the planetary nature of the candidate or to exclude an orbital signature. An analysis of the behaviour of the bisector for active dwarfs of different spectral types shows that the relation between the bisector and the radial-velocity variation depends in a great extent on the v sin(i) of the star. The results may shed a new light on the intrinsic sources of radial-velocity variation for different types of solar-type dwarfs.

astro-ph↗

arXiv2000

Accurate masses of very low mass stars: III 16 new or improved masses

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.

astro-ph↗

arXiv2000

Accurate masses of very low mass stars: IV Improved mass-luminosity relations

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.

astro-ph↗

arXiv2000

A Lack of Planets in 47 Tucanae from an HST Search

We report results from a large Hubble Space Telescope project to observe a significant (~34,000) ensemble of main sequence stars in the globular cluster 47 Tucanae with a goal of defining the frequency of inner-orbit, gas-giant planets. Simulations based on the characteristics of the 8.3 days of time-series data in the F555W and F814W WFPC2 filters show that ~17 planets should be detected by photometric transit signals if the frequency of hot Jupiters found in the solar neighborhood is assumed to hold for 47 Tuc. The experiment provided high-quality data sufficient to detect planets. A full analysis of these WFPC2 data reveals ~75 variables, but NO light curves resulted for which a convincing interpretation as a planet could be made. The planet frequency in 47 Tuc is at least an order of magnitude below that for the solar neighborhood. The cause of the absence of close-in planets in 47 Tuc is not yet known; presumably the low metallicity and/or crowding of 47 Tuc interfered with planet formation, with orbital evolution to close-in positions, or with planet survival.

astro-ph↗

arXiv2000

Chemical analysis of 8 recently discovered extra-solar planet host stars

We present the chemical analysis of a new set of stars known to harbor low mass companions, namely HD 1237, HD 52265, HD 82943, HD 83443, HD 169830, and HD 202206. In addition, we have also analyzed HD 13445 and HD 7528}, already studied elsewhere. The abundances of C and alpha-elements O, S, Si, Ca and Ti are presented and discussed in the context of the metallicity distribution of the stars with extra-solar planets. We compare the metallicity distribution of stars with planets with the same distribution of field dwarfs. The results further confirm that stars with planets are over-abundant in [Fe/H].

astro-ph↗

arXiv2000

Detection of a spectroscopic transit by the planet orbiting the star HD209458

We report the first detection of a planetary transit by spectroscopic measurements. We have detected the distortion of the stellar line profiles during a planetary transit. With the ELODIE spectrograph we took a sequence of high precision radial velocities of the star HD209458 at time of a transit of its planet. We detected an anomaly in the residuals of the orbit. The shape and the amplitude of the anomaly are modeled as a change of the mean stellar line profile resulting from the planet crossing the disk of the rotating star. The planetary orbit is in the same direction as the stellar rotation. Using the photometric transit to constrain the timing and the impact parameters of the transit, we measure an angle alpha=3.9d between the orbital plane and the apparent equatorial plane as well as a vsini=3.75(+-)1.25 kms-1. With additional constrains on the inclination of the star and on the statistics of the line of sight distribution, we can set an upper limit of 30d to the angle between the orbital plane and the stellar equatorial plane.

astro-ph↗

arXiv2000

The Spectroscopic Orbit of the Planetary Companion Transiting HD209458

We report a spectroscopic orbit with period P = 3.52433 +/- 0.00027 days for the planetary companion that transits the solar-type star HD209458. For the metallicity, mass, and radius of the star we derive [Fe/H] = 0.00 +/- 0.02, M = 1.1 +/- 0.1 solar masses, and R = 1.3 +/- 0.1 solar radii. This is based on a new analysis of the iron lines in our HIRES template spectrum, and also on the absolute magnitude and color of the star, and 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 = 85.2 +/- 1.4 degrees. For the planet we derive a mass of Mp = 0.69 +/- 0.05 Jupiter masses, a radius of Rp = 1.54 +/- 0.18 Jupiter radii, and a density of 0.23 +/- 0.08 grams per cubic cm.

astro-ph↗

arXiv1999

A planet orbiting the star Gliese 86

A 4MJ planet with a 15.8day orbital period has been detected from very precise radial velocity measurements with the CORALIE echelle spectrograph. A second remote and more massive companion has also been detected. All the planetary companions so far detected in orbit closer than 0.08 AU have a parent star with a statistically higher metal content compared to the metallicity distribution of other stars with planets. Different processes occuring during their formation may provide a possible explanation for this observation.

astro-ph↗

arXiv1999

Accurate masses of very low mass stars: II The very low mass triple system Gl 866

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.

astro-ph↗

arXiv1998

New neighbours. I. 13 new companions to nearby M dwarfs

We present preliminary results of a radial-velocity search for companions to a volume limited sample of M dwarfs. Typical accuracy range between 10m/s for the brighter stars and 70m/s at our limiting magnitude. We complement the radial velocity monitoring with adaptive optics imaging to identify close visual companions in a larger volume-limited sample. For stellar companions the two techniques together cover the full separation range, to beyond the limiting distance of the sample. We will therefore eventually obtain a statistically meaningful inventory of the stellar multiplicity of nearby M-dwarf systems. We also have useful sensitivity to giant planets, as illustrated by our recent detection of a planetary companion to Gl 876. After 2.5 years, we have discovered 12 previously unknown components in this 127 stars sample. 7 of these are actually beyond our 9 pc limit, and were included on the basis of photometric parallaxes which were biased-down by the unrecognized companion. The remaining 5 are true additions to the 9 pc inventory. More are certainly forthcoming, given our present selection bias towards short periods and relatively massive companions. We have derived orbital elements for 7 of the new systems, and for some previously known binaries. One system is a Post-Common-Envelope WD+M binary. Some of the new binaries have excellent prospects for an accurate mass determination over the next few years. Preliminary masses have accuracies of 2% at 0.4-0.6 \Msol and 10% at 0.1 \Msol.

astro-ph↗

arXiv1998

The rotational velocity of low-mass stars in the Pleiades

We present new vsini measurements for 235 low-mass stars in the Pleiades. The differential rotational broadening has been resolved for all the stars in our sample. These results, combined with previously published measurements, provide a complete and unbiased rotation data set for stars in the mass range from 0.6 to 1.2 Msol. Applying a numerical inversion technique on the vsini distributions, we derive the distributions of velocities for low-mass Pleiades members. Comparison of the rotational distributions of low-mass members between IC 2602/2391 and the Pleiades suggests that G dwarfs behave like solid-bodies and follow Skumanich's law during this time span. However, comparison between Pleiades and older clusters (M34 and Hyades) indicates that the braking of slow rotators on the early main sequence is weaker than predicted by an asymptotical Skumanich's law. This strongly supports the view that angular momentum tapped in the radiative core of slow rotators on the zero age main sequence (ZAMS) resurfaces into the convective envelope between Pleiades and Hyades age. For the G-dwarfs, we derive a characteristic coupling time scale between the core and the envelope of about 100--200Myr. The relationship between rotation and coronal activity in the Pleiades is in agreement with previous observations in other clusters and field stars. We show that the Rossby diagram provides an excellent description of the X-ray activity for all stars in the mass domain studied. The Pleiades data for slow and moderate rotators fills the gap between the X-ray--rotation correlation found for slow rotators and the X-ray ``saturation plateau'' observed for young fast rotators.

astro-ph↗

arXiv1998

Insights into the formation of barium and Tc-poor S stars from an extended sample of orbital elements

The set of orbital elements available for chemically-peculiar red giant (PRG) stars has been considerably enlarged thanks to a decade-long CORAVEL radial-velocity monitoring of about 70 barium stars and 50 S stars. This paper presents a detailed analysis of the complete set of orbital parameters available for PRG stars; the individual data are given in three companion papers. The main results are as follows: (i) The similarity between the orbital parameters of Tc-poor S stars and barium stars confirms that Tc-poor S stars are the cooler analogs of barium stars; (ii) The eccentricity -- period diagram of PRG stars clearly bears the signature of dissipative processes associated with mass transfer; (iii) The mass function distribution is compatible with the unseen companion being a white dwarf (WD); (iv) Assuming that the WD companion has a mass in the range 0.60+-0.04 Msun, the masses of mild and strong barium stars amount to 1.9+-0.2 and 1.5+-0.2 Msun, respectively; (v) Mild barium stars are not restricted to long-period systems; the difference between mild and strong barium stars is mainly one of galactic population rather than of orbital separation, in agreement with their respective kinematical properties; (vi) Binarity is probably not a sufficient condition to produce a PRG star, and a metallicity lower than solar seems to be required as well.

astro-ph↗

arXiv1998

A CORAVEL radial-velocity monitoring of giant Ba and S stars: spectroscopic orbits and intrinsic variations

This paper provides orbital parameters for 38 barium stars and 10 extrinsic S stars derived from a decade-long CORAVEL monitoring. Lower bounds on the orbital period (generally exceeding 10 y) have been obtained for 10 more systems. Mira S, SC and (Tc-poor) C stars have also been monitored and show intrinsic radial-velocity variations due to atmospheric phenomena. Tentative orbital solutions are proposed for 3 stars (S UMa, X Cnc, BD-08:1900) where the velocity and photometric periods are different. Three stars (RZ Peg, SS Vir and R CMi) exhibit radial-velocity variations synchronous with the light variations. Pseudo-orbital solutions have been derived for those stars. In the case of RZ Peg, a line-doubling phenomenon is observed near maximum light, and probably reflects the shock wave propagating through the photosphere.

astro-ph↗

arXiv1997

The HIPPARCOS Hertzsprung-Russell diagram of S stars: Probing nucleosynthesis and dredge-up

HIPPARCOS trigonometrical parallaxes make it possible to compare the location of Tc-rich and Tc-poor S stars in the Hertzsprung-Russell (HR) diagram: Tc-rich S stars are found to be cooler and intrinsically brighter than Tc-poor S stars. The comparison with the Geneva evolutionary tracks reveals that the line marking the onset of thermal pulses on the asymptotic giant branch (AGB) matches well the observed limit between Tc-poor and Tc-rich S stars. Tc-rich S stars are, as expected, identified with thermally-pulsing AGB stars of low and intermediate masses, whereas Tc-poor S stars comprise mostly low-mass stars (with the exception of 57 Peg) located either on the red giant branch or on the early AGB. Like barium stars, Tc-poor S stars are known to belong exclusively to binary systems, and their location in the HR diagram is consistent with the average mass of 1.6 +- 0.2 Msun derived from their orbital mass-function distribution. A comparison with the S stars identified in the Magellanic Clouds and in the Fornax dwarf elliptical galaxy reveals that they have luminosities similar to the galactic Tc-rich S stars. However, most of the surveys of S stars in the external systems did not reach the lower luminosities at which galactic Tc-poor S stars are found. The deep Westerlund survey of carbon stars in the SMC uncovered a family of faint carbon stars that may be the analogues of the low-luminosity, galactic Tc-poor S stars.

astro-ph↗

arXiv1996

The Stellar Dynamics of Omega Centauri

The stellar dynamics of Omega Centauri are inferred from the radial velocities of 469 stars measured with CORAVEL (Mayor et al. 1997). Rather than fit the data to a family of models, we generate estimates of all dynamical functions nonparametrically, by direct operation on the data. The cluster is assumed to be oblate and edge-on but mass is not assumed to follow light. The mean motions are consistent with axisymmetry but the rotation is not cylindrical. The peak rotational velocity is 7.9 km/s at 11 pc from the center. The apparent rotation of Omega Centauri is attributable in part to its proper motion. We reconstruct the stellar velocity ellipsoid as a function of position, assuming isotropy in the meridional plane. We find no significant evidence for a difference between the velocity dispersions parallel and perpendicular to the meridional plane. The mass distribution inferred from the kinematics is slightly more extended than, though not strongly inconsistent with, the luminosity distribution. We also derive the two-integral distribution function f(E,Lz) implied by the velocity data.

astro-ph↗