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Spectroscopic parameters for a sample of metal-rich solar-type stars
Aims.To date, metallicity is the only parameter of a star that appearsto clearly correlate with the presence of planets and their properties.To check for new correlations between stars and the existence of anorbiting planet, we determine accurate stellar parameters for severalmetal-rich solar-type stars. The purpose is to fill the gap of thecomparison sample presented in previous works in the high metal-contentregime. Methods: .The stellar parameters were determined using anLTE analysis based on equivalent widths (EW) of iron lines and byimposing excitation and ionization equilibrium. We also present a firststep in determining these stellar parameters in an automatic manner byusing the code DAOSPEC for the EW determination. Results:.Accurate stellar parameters and metallicities are obtained for oursample composed of 64 high metal-content stars not known to harbor anyplanet. This sample will in the future give us the possibility of betterexploring the existence of differences in the chemical abundancesbetween planet-host stars and stars without known planets in themetal-rich domain. We also report stellar parameters for some recentlydiscovered planet-host stars. Finally, we present an empiricalcalibration for DAOSPEC based on the comparison between its EWmeasurements and the standard "hand made" measurements for the FEROSsample presented in this paper.
| Basic physical parameters of a selected sample of evolved stars
We present the detailed spectroscopic analysis of 72 evolved stars,which were previously studied for accurate radial velocity variations.Using one Hyades giant and another well studied star as the referenceabundance, we determine the [Fe/H] for the whole sample. Thesemetallicities, together with the T_eff values and the absolute V-bandmagnitude derived from Hipparcos parallaxes, are used to estimate basicstellar parameters (ages, masses, radii, (B-V)0 and log g)using theoretical isochrones and a Bayesian estimation method. The(B-V)0 values so estimated turn out to be in excellentagreement (to within ~0.05 mag) with the observed (B-V), confirming thereliability of the T_eff-(B-V)0 relation used in theisochrones. On the other hand, the estimated log g values are typically0.2 dex lower than those derived from spectroscopy; this effect has anegligible impact on [Fe/H] determinations. The estimated diametersθ have been compared with limb darkening-corrected ones measuredwith independent methods, finding an agreement better than 0.3 maswithin the 1<θ<10 mas interval (or, alternatively, findingmean differences of just 6%). We derive the age-metallicity relation forthe solar neighborhood; for the first time to our knowledge, such arelation has been derived from observations of field giants rather thanfrom open clusters and field dwarfs and subdwarfs. The age-metallicityrelation is characterized by close-to-solar metallicities for starsyounger than ~4 Gyr, and by a large [Fe/H] spread with a trend towardslower metallicities for higher ages. In disagreement with other studies,we find that the [Fe/H] dispersion of young stars (less than 1 Gyr) iscomparable to the observational errors, indicating that stars in thesolar neighbourhood are formed from interstellar matter of quitehomogeneous chemical composition. The three giants of our sample whichhave been proposed to host planets are not metal rich; this result is atodds with those for main sequence stars. However, two of these starshave masses much larger than a solar mass so we may be sampling adifferent stellar population from most radial velocity searches forextrasolar planets. We also confirm the previous indication that theradial velocity variability tends to increase along the RGB, and inparticular with the stellar radius.
| Habitability of Known Exoplanetary Systems Based on Measured Stellar Properties
Habitable planets are likely to be broadly Earth-like in composition,mass, and size. Masses are likely to be within a factor of a few of theEarth's mass. Currently, we do not have sufficiently sensitivetechniques to detect Earth-mass planets, except in rare circumstances.It is thus necessary to model the known exoplanetary systems. Inparticular, we need to establish whether Earth-mass planets could bepresent in the classical habitable zone (HZ) or whether the giantplanets that we know to be present would have gravitationally ejectedEarth-mass planets or prevented their formation. We have answered thisquestion by applying computer models to the 152 exoplanetary systemsknown by 2006 April 18 that are sufficiently well characterized for ouranalysis. For systems in which there is a giant planet, inside the HZ,which must have arrived there by migration, there are two cases: (1)where the migration of the giant planet across the HZ has not ruled outthe existence of Earth-mass planets in the HZ; and (2) where themigration has ruled out existence. For each case, we have determined theproportion of the systems that could contain habitable Earth-massplanets today, and the proportion for which this has been the case forat least the past 1000 Myr (excluding any early heavy bombardment). Forcase 1 we get 60% and 50%, respectively, and for case 2 we get 7% and7%, respectively.
| Confirmation of the planet hypothesis for the long-period radial velocity variations of β Geminorum
Aims.Our aim is to confirm the nature of the long period radial velocitymeasurements for β Gem first found by Hatzes & Cochran (1993). Methods: .We present precise stellar radial velocity measurementsfor the K giant star β Gem spanning over 25 years. An examinationof the Ca II K emission, spectral line shapes from high resolution data(R = 210 000), and Hipparcos photometry was also made to discern thetrue nature of the long period radial velocity variations. Results: . The radial velocity data show that the long period, lowamplitude radial velocity variations found by Hatzes & Cochran(1993) are long-lived and coherent. Furthermore, the Ca II K emission,spectral line bisectors, and Hipparcos photometry show no significantvariations of these quantities with the radial velocity period. Anorbital solution assuming a stellar mass of 1.7 M_ȯ yields aperiod, P = 589.6 days, a minimum mass of 2.3 M_Jupiter, and asemi-major axis, a = 1.6 AU. The orbit is nearly circular (e = 0.02). Conclusions: .The data presented here confirm the planetarycompanion hypothesis suggested by Hatzes & Cochran (1993). βGem is one of six intermediate mass stars known to host a sub-stellarcompanion and suggests that planet-formation around stars much moremassive than the sun may common.
| Two Suns in The Sky: Stellar Multiplicity in Exoplanet Systems
We present results of a reconnaissance for stellar companions to all 131radial velocity-detected candidate extrasolar planetary systems known asof 2005 July 1. Common proper-motion companions were investigated usingthe multiepoch STScI Digitized Sky Surveys and confirmed by matching thetrigonometric parallax distances of the primaries to companion distancesestimated photometrically. We also attempt to confirm or refutecompanions listed in the Washington Double Star Catalog, in the Catalogsof Nearby Stars Series by Gliese and Jahreiß, in Hipparcosresults, and in Duquennoy & Mayor's radial velocity survey. Ourfindings indicate that a lower limit of 30 (23%) of the 131 exoplanetsystems have stellar companions. We report new stellar companions to HD38529 and HD 188015 and a new candidate companion to HD 169830. Weconfirm many previously reported stellar companions, including six starsin five systems, that are recognized for the first time as companions toexoplanet hosts. We have found evidence that 20 entries in theWashington Double Star Catalog are not gravitationally bound companions.At least three (HD 178911, 16 Cyg B, and HD 219449), and possibly five(including HD 41004 and HD 38529), of the exoplanet systems reside intriple-star systems. Three exoplanet systems (GJ 86, HD 41004, andγ Cep) have potentially close-in stellar companions, with planetsat roughly Mercury-Mars distances from the host star and stellarcompanions at projected separations of ~20 AU, similar to the Sun-Uranusdistance. Finally, two of the exoplanet systems contain white dwarfcompanions. This comprehensive assessment of exoplanet systems indicatesthat solar systems are found in a variety of stellar multiplicityenvironments-singles, binaries, and triples-and that planets survive thepost-main-sequence evolution of companion stars.
| The Hunt for Extrasolar Planets at McDonald Observatory
Currently every major telescope at McDonald Observatory is utilized inthe search for extrasolar planets. We review the different planet searchefforts and present the results of these programs. In particular wedescribe in detail the on-going precise Doppler surveys at the Harlan J.Smith 2.7 m telescope and at the Hobby-Eberly Telescope (HET). Thehighlight of the HET program was last year's discovery of a "HotNeptune" in the ρ planetary system. With a mass of only 17 Earthmasses this object demonstrates our ability to detect extrasolar planetswith masses below the gas giant range.
| High-Resolution Spectroscopy of the Planetary Host HD 13189: Highly Evolved and Metal-poor
We report on the abundances of 13 elements in the planetary host HD13189, a massive giant star. Abundances are found to be subsolar, with[Fe/H]=-0.58+/-0.04 HD 13189 is one of the most metal-poor planetaryhosts yet discovered. Abundance ratios relative to Fe show nopeculiarities with respect to random field stars. A census ofmetallicities of the seven currently known planet-harboring giantsresults in a distribution that is more metal-poor than the well-knownmetal-rich distribution of main-sequence (MS) planetary hosts. Thisfinding is discussed in terms of accretion of H-depleted material, oneof the possible mechanisms responsible for the high-metallicitydistribution of MS stars with planets. We estimate the mass of the HD13189 progenitor to be 3.5 Msolar but cannot constrain thisvalue to better than 2-6 Msolar. A stellar mass of 3.5Msolar implies a planetary mass ofmsini=14.0MJ+/-0.8MJ, placing the companion at theplanet/brown dwarf boundary. Given its physical characteristics, the HD13189 system is potentially unique among planetary systems, and itscontinued investigation should provide invaluable data to extrasolarplanetary research.Based on observations obtained at the 2 m Alfred Jensch telescope at theThüringer Landessternwarte Tautenburg, Tautenburg, Germany.
| A substellar companion around the intermediate-mass giant star HD 11977
We report the discovery of a substellar companion to theintermediate-mass star HD 11977 (G5 III). Radialvelocities of this star have been monitored for five years with FEROS atthe 1.52-m ESO and later at the 2.2-m MPG/ESO telescope in La Silla,Chile. Based on the collected data we calculated an orbital solutionwith a period of P=711 days, a semi-amplitude of K1=105 ms-1, and an eccentricity of e=0.4. The period of theradial-velocity variation is longer than that of the estimated stellarrotation, rendering it unlikely that rotational modulation is the sourceof the variation in the radial velocity. This hypothesis is supported bythe absence of a correlation between stellar activity indicators andradial-velocity variation. By determining a primary stellar mass ofMstar=1.91 Mȯ, the best-fit minimum mass ofthe companion and semi-major axis of the orbit arem2sin{i}=6.54 MJup and a2=1.93 AU,respectively. An upper limit for the mass of the companion ofm2 65.5 MJup has been calculated fromHipparcos astrometric measurements. Although the possibility of abrown-dwarf companion cannot be excluded, HD 11977 B is one of the fewplanet candidates detected around an intermediate-mass star. Theprogenitor main-sequence star of HD 11977 is probablyan A-type star. This discovery gives an indirect evidence for planetarycompanions around early type main-sequence stars.
| Spectroscopic metallicities for planet-host stars: Extending the samples
We present stellar parameters and metallicities for 29 planet-hoststars, as well as for a large volume-limited sample of 53 stars notknown to be orbited by any planetary-mass companion. These stars add tothe results presented in our previous series of papers, providing twolarge and uniform samples of 119 planet-hosts and 94“single” stars with accurate stellar parameters and [Fe/H]estimates. The analysis of the results further confirms that stars withplanets are metal-rich when compared with average field dwarfs.Important biases that may compromise future studies are also discussed.Finally, we compare the metallicity distributions for singleplanet-hosts and planet-hosts in multiple stellar systems. The resultsshow that a small difference cannot be excluded, in the sense that thelatter sample is slighly overmetallic. However, more data are needed toconfirm this correlation.
| A giant planet around the massive giant star HD 13189
Most extrasolar planet discoveries using radial velocity measurementshave been for solar-like G-stars. In order to understand better the rolestellar mass for the formation of planets we must learn more about thefrequency of planetary companions around both high- and low-mass stars.Radial velocity searches for planets around high mass main-sequencestars are difficult due to the paucity of lines and often rapid rotationof these early-type stars. On the other hand, evolved stars that havemoved off the main sequence offer us the possibility of searching forplanets around higher mass stars by means of precise radial velocitymeasurements. Here we present radial velocity measurements for the starHD 13189 using measurements taken at the Thüringer LandessternwarteTautenburg, the Harlan J. Smith Telescope at McDonald Observatory, andthe Hobby-Eberly Telescope. We classify the spectral type of this staras K2 with luminosity class II. The radial velocity measurements showlong-period variations with a period of 472 days and an amplitude of 173m s-1. The Ca II S-index is consistent with an inactive starand this shows no variations with the radial velocity period. We alsoinvestigated possible changes in the line shapes by measuring spectralline bisectors. These show no variations with the radial velocityperiod. We interpret the 472-day period as being caused by a sub-stellarcompanion. Based on the estimated absolute magnitude and a comparison toevolutionary tracks we estimate the mass of the progenitor star between2 and 7 M_ȯ which results in a projected mass of the companion of msin i = 8 20 M_J. HD 13189 may be the most massive star known to possessan extrasolar planet. This suggests that the formation of giant planetscan also occur around early-type stars. HD 13189 also shows significantshort term radial velocity variability on time scales of days that ismost likely due to stellar oscillations. This behavior is typical for Kgiant stars.
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
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Osservazione e dati astrometrici
| Costellazione: | Triangolo |
| Ascensione retta: | 02h09m40.17s |
| Declinazione: | +32°18'59.2" |
| Magnitudine apparente: | 7.571 |
| Distanza: | 1851.852 parsec |
| Moto proprio RA: | 2.3 |
| Moto proprio Dec: | 5.3 |
| B-T magnitude: | 9.508 |
| V-T magnitude: | 7.731 |
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