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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.
| Catalog of Nearby Exoplanets
We present a catalog of nearby exoplanets. It contains the 172 knownlow-mass companions with orbits established through radial velocity andtransit measurements around stars within 200 pc. We include fivepreviously unpublished exoplanets orbiting the stars HD 11964, HD 66428,HD 99109, HD 107148, and HD 164922. We update orbits for 83 additionalexoplanets, including many whose orbits have not been revised sincetheir announcement, and include radial velocity time series from theLick, Keck, and Anglo-Australian Observatory planet searches. Both thesenew and previously published velocities are more precise here due toimprovements in our data reduction pipeline, which we applied toarchival spectra. We present a brief summary of the global properties ofthe known exoplanets, including their distributions of orbital semimajoraxis, minimum mass, and orbital eccentricity.Based on observations obtained at the W. M. Keck Observatory, which isoperated jointly by the University of California and the CaliforniaInstitute of Technology. The Keck Observatory was made possible by thegenerous financial support of the W. M. Keck Foundation.
| Chemical Composition of the Planet-harboring Star TrES-1
We present a detailed chemical abundance analysis of the parent star ofthe transiting extrasolar planet TrES-1. Based on high-resolution KeckHIRES and Hobby-Eberly Telescope HRS spectra, we have determinedabundances relative to the Sun for 16 elements (Na, Mg, Al, Si, Ca, Sc,Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, and Ba). The resulting averageabundance of <[X/H]>=-0.02+/-0.06 is in good agreement withinitial estimates of solar metallicity based on iron. We compare theelemental abundances of TrES-1 with those of the sample of stars withplanets, searching for possible chemical abundance anomalies. TrES-1appears not to be chemically peculiar in any measurable way. Weinvestigate possible signs of selective accretion of refractory elementsin TrES-1 and other stars with planets and find no statisticallysignificant trends of metallicity [X/H] with condensation temperatureTc. We use published abundances and kinematic information forthe sample of planet-hosting stars (including TrES-1) and severalstatistical indicators to provide an updated classification in terms oftheir likelihood to belong to either the thin disk or the thick disk ofthe Milky Way. TrES-1 is found to be very likely a member of thethin-disk population. By comparing α-element abundances of planethosts and a large control sample of field stars, we also find thatmetal-rich ([Fe/H]>~0.0) stars with planets appear to besystematically underabundant in [α/Fe] by ~0.1 dex with respect tocomparison field stars. The reason for this signature is unclear, butsystematic differences in the analysis procedures adopted by differentgroups cannot be ruled out.
| Tertiary companions to close spectroscopic binaries
We have surveyed a sample of 165 solar-type spectroscopic binaries (SB)with periods from 1 to 30 days for higher-order multiplicity. Asubsample of 62 targets were observed with the NACO adaptive opticssystem and 13 new physical tertiary companions were detected. Anadditional 12 new wide companions (5 still tentative) were found usingthe 2MASS all-sky survey. The binaries belong to 161 stellar systems; ofthese 64 are triple, 11 quadruple and 7 quintuple. After correction forincompleteness, the fraction of SBs with additional companions is foundto be 63% ± 5%. We find that this fraction is a strong functionof the SB period P, reaching 96% for P<3d and dropping to34% for P>12^d. Period distributions of SBs with and withouttertiaries are significantly different, but their mass ratiodistributions are identical. The statistical data on the multiplicity ofclose SBs presented in this paper indicates that the periods and massratios of SBs were established very early, but the periods of SB systemswith triples were further shortened by angular momentum exchange withcompanions.
| Abundances of refractory elements in the atmospheres of stars with extrasolar planets
Aims.This work presents a uniform and homogeneous study of chemicalabundances of refractory elements in 101 stars with and 93 without knownplanetary companions. We carry out an in-depth investigation of theabundances of Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Na, Mg and Al. The newcomparison sample, spanning the metallicity range -0.70< [Fe/H]<0.50, fills the gap that previously existed, mainly at highmetallicities, in the number of stars without known planets.Methods.Weused an enlarged set of data including new observations, especially forthe field "single" comparison stars . The line list previously studiedby other authors was improved: on average we analysed 90 spectral linesin every spectrum and carefully measured more than 16 600 equivalentwidths (EW) to calculate the abundances.Results.We investigate possibledifferences between the chemical abundances of the two groups of stars,both with and without planets. The results are globally comparable tothose obtained by other authors, and in most cases the abundance trendsof planet-host stars are very similar to those of the comparison sample.Conclusions.This work represents a step towards the comprehension ofrecently discovered planetary systems. These results could also beuseful for verifying galactic models at high metallicities andconsequently improve our knowledge of stellar nucleosynthesis andgalactic chemical evolution.
| Ground-based direct detection of close-in extra-solar planets with nulling and high order adaptive optics
Ground-based direct detection of extra-solar planets is very challengingdue to high planet to star brightness contrasts. For giant close-inplanets, such as have been discovered by the radial velocity method,closer than 0.1 AU, the reflected light is predicted to be fairly highyielding a contrast ratio ranging from 10-4 to10-5 at near infra-red wavelengths. In this paper, weinvestigate direct detection of reflected light from such planets usingnulling interferometry, and high-order adaptive optics in conjunctionwith large double aperture ground-based telescopes. In thisconfiguration, at least 10-3 suppression of the entirestellar Airy pattern with small loss of planet flux as close as 0.03arcsec is achievable. Distinguishing residual starlight from the planetsignal is achieved by using the center of gravity shift method ormulticolor differential imaging. Using these assumptions, we deriveexposure times from a few minutes to several hours for direct detectionof many of the known extra-solar planets with several short-baselinedouble aperture telescopes such as the Large Binocular Telescope (LBT),the Very Large Telescope (VLT) and the Keck Telescope.
| Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs
We present a uniform catalog of stellar properties for 1040 nearby F, G,and K stars that have been observed by the Keck, Lick, and AAT planetsearch programs. Fitting observed echelle spectra with synthetic spectrayielded effective temperature, surface gravity, metallicity, projectedrotational velocity, and abundances of the elements Na, Si, Ti, Fe, andNi, for every star in the catalog. Combining V-band photometry andHipparcos parallaxes with a bolometric correction based on thespectroscopic results yielded stellar luminosity, radius, and mass.Interpolating Yonsei-Yale isochrones to the luminosity, effectivetemperature, metallicity, and α-element enhancement of each staryielded a theoretical mass, radius, gravity, and age range for moststars in the catalog. Automated tools provide uniform results and makeanalysis of such a large sample practical. Our analysis method differsfrom traditional abundance analyses in that we fit the observed spectrumdirectly, rather than trying to match equivalent widths, and wedetermine effective temperature and surface gravity from the spectrumitself, rather than adopting values based on measured photometry orparallax. As part of our analysis, we determined a new relationshipbetween macroturbulence and effective temperature on the main sequence.Detailed error analysis revealed small systematic offsets with respectto the Sun and spurious abundance trends as a function of effectivetemperature that would be inobvious in smaller samples. We attempted toremove these errors by applying empirical corrections, achieving aprecision per spectrum of 44 K in effective temperature, 0.03 dex inmetallicity, 0.06 dex in the logarithm of gravity, and 0.5 kms-1 in projected rotational velocity. Comparisons withprevious studies show only small discrepancies. Our spectroscopicallydetermined masses have a median fractional precision of 15%, but theyare systematically 10% higher than masses obtained by interpolatingisochrones. Our spectroscopic radii have a median fractional precisionof 3%. Our ages from isochrones have a precision that variesdramatically with location in the Hertzsprung-Russell diagram. We planto extend the catalog by applying our automated analysis technique toother large stellar samples.
| Plasma and Magnetic Field Parameters in the Vicinity of Short-periodic Giant Exoplanets
During the past years, more than 130 giant planets were discovered inextrasolar planetary systems. Because of the fact that the orbitaldistances are very close to their host stars, these planets are embeddedin a dense stellar wind, which can pick up planetary ions. We model thestellar wind interaction of the short-periodic exoplanets OGLE-TR-56band HD 209458b at their orbital distances of ~0.023 AU and ~0.045 AU, bycalculating the Alfvén Mach number and the magnetosonic Machnumber in the stellar wind plasma flow. We then analyze the differentplasma interaction regimes around the planetary obstacles, which appearfor different stellar wind parameters. Our study shows that the stellarwind plasma parameters like temperature, interplanetary magnetic field,particle density, and velocity near planetary obstacles at orbitaldistances closer than 0.1-0.2 AU have conditions such that no bow shocksevolve. Our study shows also that these close-in exoplanets are in asubmagnetosonic regime comparable to the magnetospheric plasmainteraction of the inner satellites of Jupiter and Saturn. Furthermore,we compare the results achieved for both exoplanets with theJupiter-class exoplanet HD 28185b at its orbital distance of ~1.03 AU.Finally, we also discuss the behavior of the stellar wind plasma flowclose to the planetary obstacles of two highly eccentric gas giants,namely, HD 108147b and HD 162020b. Because of their eccentric orbits,these two exoplanets periodically experience both regimes with andwithout a bow shock. Finally, we simulate the neutral gas density of HD209458b with a Monte Carlo model. By using the plasma parametersobtained in our study we calculate the ion production and loss rate ofH+ with a test particle model. Our simulations yieldH+ loss rates for HD 209458b or similar giant exoplanets inorders of about 108-109 g s-1. Theseion loss rates are at least 1 order of magnitude lower than the observedloss rate of evaporating neutral H atoms. Our study indicates, thatsimilar gas giants at larger orbital distances have lower ion lossrates. Thus, the dominating component of particle loss of short-periodicJupiter-class exoplanets will be neutral hydrogen.
| The Planet-Metallicity Correlation
We have recently carried out spectral synthesis modeling to determineTeff, logg, vsini, and [Fe/H] for 1040 FGK-type stars on theKeck, Lick, and Anglo-Australian Telescope planet search programs. Thisis the first time that a single, uniform spectroscopic analysis has beenmade for every star on a large Doppler planet search survey. We identifya subset of 850 stars that have Doppler observations sufficient todetect uniformly all planets with radial velocity semiamplitudes K>30m s-1 and orbital periods shorter than 4 yr. From this subsetof stars, we determine that fewer than 3% of stars with-0.5<[Fe/H]<0.0 have Doppler-detected planets. Above solarmetallicity, there is a smooth and rapid rise in the fraction of starswith planets. At [Fe/H]>+0.3 dex, 25% of observed stars have detectedgas giant planets. A power-law fit to these data relates the formationprobability for gas giant planets to the square of the number of metalatoms. High stellar metallicity also appears to be correlated with thepresence of multiple-planet systems and with the total detected planetmass. This data set was examined to better understand the origin of highmetallicity in stars with planets. None of the expected fossilsignatures of accretion are observed in stars with planets relative tothe general sample: (1) metallicity does not appear to increase as themass of the convective envelopes decreases, (2) subgiants with planetsdo not show dilution of metallicity, (3) no abundance variations for Na,Si, Ti, or Ni are found as a function of condensation temperature, and(4) no correlations between metallicity and orbital period oreccentricity could be identified. We conclude that stars with extrasolarplanets do not have an accretion signature that distinguishes them fromother stars; more likely, they are simply born in higher metallicitymolecular clouds.Based on observations obtained at Lick and Keck Observatories, operatedby the University of California, and the Anglo-Australian Observatories.
| Prospects for Habitable ``Earths'' in Known Exoplanetary Systems
We have examined whether putative Earth-mass planets could remainconfined to the habitable zones (HZs) of the 111 exoplanetary systemsconfirmed by 2004 August. We find that in about half of these systemsthere could be confinement for at least the past 1000 Myr, though insome cases only in variously restricted regions of the HZ. The HZmigrates outward during the main-sequence lifetime, and we find that inabout two-thirds of the systems an Earth-mass planet could be confinedto the HZ for at least 1000 Myr sometime during the main-sequencelifetime. Clearly, these systems should be high on the target list forexploration for terrestrial planets. We have reached our conclusions bydetailed investigations of seven systems, which has resulted in anestimate of the distance from the giant planet within which orbitalstability is unlikely for an Earth-mass planet. This distance is givenby nRH, where RH is the Hill radius of the giantplanet and n is a multiplier that depends on the giant's orbitaleccentricity and on whether the Earth-mass planet is interior orexterior to the giant planet. We have estimated n for each of the sevensystems by launching Earth-mass planets in various orbits and followingtheir fate with a hybrid orbital integrator. We have then evaluated thehabitability of the other exoplanetary systems using nRHderived from the giant's orbital eccentricity without carrying outtime-consuming orbital integrations. A stellar evolution model has beenused to obtain the HZs throughout the main-sequence lifetime.
| On the ages of exoplanet host stars
We obtained spectra, covering the CaII H and K region, for 49 exoplanethost (EH) stars, observable from the southern hemisphere. We measuredthe chromospheric activity index, R'{_HK}. We compiled previouslypublished values of this index for the observed objects as well as theremaining EH stars in an effort to better smooth temporal variations andderive a more representative value of the average chromospheric activityfor each object. We used the average index to obtain ages for the groupof EH stars. In addition we applied other methods, such as: Isochrone,lithium abundance, metallicity and transverse velocity dispersions, tocompare with the chromospheric results. The kinematic method is a lessreliable age estimator because EH stars lie red-ward of Parenago'sdiscontinuity in the transverse velocity dispersion vs dereddened B-Vdiagram. The chromospheric and isochrone techniques give median ages of5.2 and 7.4 Gyr, respectively, with a dispersion of 4 Gyr. The medianage of F and G EH stars derived by the isochrone technique is 1-2 Gyrolder than that of identical spectral type nearby stars not known to beassociated with planets. However, the dispersion in both cases is large,about 2-4 Gyr. We searched for correlations between the chromosphericand isochrone ages and L_IR/L* (the excess over the stellarluminosity) and the metallicity of the EH stars. No clear tendency isfound in the first case, whereas the metallicy dispersion seems toslightly increase with age.
| Abundances of Na, Mg and Al in stars with giant planets
We present Na, Mg and Al abundances in a set of 98 stars with knowngiant planets, and in a comparison sample of 41 “single”stars. The results show that the [X/H] abundances (with X = Na, Mg andAl) are, on average, higher in stars with giant planets, a resultsimilar to the one found for iron. However, we did not find any strongdifference in the [X/Fe] ratios, for a fixed [Fe/H], between the twosamples of stars in the region where the samples overlap. The data wasused to study the Galactic chemical evolution trends for Na, Mg and Aland to discuss the possible influence of planets on this evolution. Theresults, similar to those obtained by other authors, show that the[X/Fe] ratios all decrease as a function of metallicity up to solarvalues. While for Mg and Al this trend then becomes relatively constant,for Na we find indications of an upturn up to [Fe/H] values close to0.25 dex. For metallicities above this value the [Na/Fe] becomesconstant.
| On the possible correlation between the orbital periods of extrasolar planets and the metallicity of the host stars
We investigate a possible correlation between the orbital periods P ofthe extrasolar planet sample and the metallicity [Fe/H] of their parentstars. Close-in planets, on orbits of a few days, are more likely to befound around metal-rich stars. Simulations show that a weak correlationis present. This correlation becomes stronger when only single starswith one detected planet are considered. We discuss several potentialsources of bias that might mimic the correlation, and find that they canbe ruled out, but not with high significance. If real, the absence ofvery short-period planets around the stellar sample with [Fe/H] < 0.0can be interpreted as evidence of a metallicity dependence of themigration rates of giant planets during formation in the protoplanetarydisc. The observed P-[Fe/H] correlation can be falsified or confirmed byconducting spectroscopic or astrometric surveys of metal-poor stars([Fe/H] < -0.5) in the field.
| The Radiometric Bode's Law and Extrasolar Planets
We predict the radio flux densities of the extrasolar planets in thecurrent census, making use of an empirical relation-the radiometricBode's law-determined from the five ``magnetic'' planets in the solarsystem (the Earth and the four gas giants). Radio emission from theseplanets results from solar wind-powered electron currents depositingenergy in the magnetic polar regions. We find that most of the knownextrasolar planets should emit in the frequency range 10-1000 MHz and,under favorable circumstances, have typical flux densities as large as 1mJy. We also describe an initial, systematic effort to search for radioemission in low radio frequency images acquired with the Very LargeArray (VLA). The limits set by the VLA images (~300 mJy) are consistentwith, but do not provide strong constraints on, the predictions of themodel. Future radio telescopes, such as the Low Frequency Array and theSquare Kilometer Array, should be able to detect the known extrasolarplanets or place austere limits on their radio emission. Planets withmasses much lower than those in the current census will probably radiatebelow 10 MHz and will require a space-based array.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are 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/418/989
| Spectroscopic [Fe/H] for 98 extra-solar planet-host stars. Exploring the probability of planet formation
We present stellar parameters and metallicities, obtained from adetailed spectroscopic analysis, for a large sample of 98 stars known tobe orbited by planetary mass companions (almost all known targets), aswell as for a volume-limited sample of 41 stars not known to host anyplanet. For most of the stars the stellar parameters are revisedversions of the ones presented in our previous work. However, we alsopresent parameters for 18 stars with planets not previously published,and a compilation of stellar parameters for the remaining 4 planet-hostsfor which we could not obtain a spectrum. A comparison of our stellarparameters with values of Teff, log g, and [Fe/H] availablein the literature shows a remarkable agreement. In particular, ourspectroscopic log g values are now very close to trigonometric log gestimates based on Hipparcos parallaxes. The derived [Fe/H] values arethen used to confirm the previously known result that planets are moreprevalent around metal-rich stars. Furthermore, we confirm that thefrequency of planets is a strongly rising function of the stellarmetallicity, at least for stars with [Fe/H] > 0. While only about 3%of the solar metallicity stars in the CORALIE planet search sample werefound to be orbited by a planet, this number increases to more than 25%for stars with [Fe/H] above +0.3. Curiously, our results also suggestthat these percentages might remain relatively constant for values of[Fe/H] lower than about solar, increasing then linearly with the massfraction of heavy elements. These results are discussed in the contextof the theories of planetary formation.Based on observations collected at the La Silla Observatory, ESO(Chile), with the CORALIE spectrograph at the 1.2-m Euler Swisstelescope and the FEROS spectrograph at the 1.52-m and 2.2-m ESOtelescopes, with the VLT/UT2 Kueyen telescope (Paranal Observatory, ESO,Chile) using the UVES spectrograph (Observing run 67.C-0206, in servicemode), with the TNG and William Herschel Telescopes, both operated atthe island of La Palma, and with the ELODIE spectrograph at the 1.93-mtelescope at the Observatoire de Haute Provence.
| Lithium in stars with exoplanets
We present a comparison of the lithium abundances of stars with andwithout planetary-mass companions. New lithium abundances are reportedin 79 planet hosts and 38 stars from a comparison sample. When the Liabundances of planet host stars are compared with the 157 stars in thesample of field stars of Chen et al. (\cite{Chen2001}) we find that theLi abundance distribution is significantly different, and that there isa possible excess of Li depletion in planet host stars with effectivetemperatures in the range 5600-5850 K, whereas we find no significantdifferences in the temperature range 5850-6350 K. We have searched forstatistically significant correlations between the Li abundance ofparent stars and various parameters of the planetary companions. We donot find any strong correlation, although there are may be a hint of apossible gap in the Li distribution of massive planet host stars.Based on observations collected at the La Silla Observatory, ESO(Chile), with the CORALIE spectrograph at the 1.2 m Euler Swisstelescope, and with the FEROS spectrograph at the 1.52 m ESO telescope,and using the UES spectrograph at the 4.2 m William Herschel Telescope(WHT) and SARG spectrograph at the 3.5 m Telescopio Nazional Galileo onLa Palma (Canary Islands).
| Search for periodicities in distribution of orbits of planets.
Not Available
| Effective temperatures and radii of planet-hosting stars from IR photometry
In this paper we present and analyse determinations of effectivetemperatures of planet-hosting stars using infrared (IR) photometry. Oneof our goals is the comparison with spectroscopic temperatures toevaluate the presence of systematic effects that could alter thedetermination of metal abundances. To estimate the stellar temperatureswe have followed a new approach based on fitting the observed 2MASS IRphotometry with accurately calibrated synthetic photometry. Special carehas been put in evaluating all sources of possible errors andincorporating them in the analysis. A comparison of our temperaturedeterminations with spectroscopic temperatures published by differentgroups reveals the presence of no systematic trends and a scattercompatible with the quoted uncertainties of 0.5-1.3%. This mutualagreement strengthens the results of both the spectroscopic and IRphotometry analyses. Comparisons with other photometric temperaturecalibrations, generally with poorer performances, are also presented. Inaddition, the method employed of fitting IR photometry naturally yieldsdeterminations of the stellar semi-angular diameters, which, whencombined with the distances, results in estimations of the stellar radiiwith remarkable accuracies of ~ 2-4%. A comparison with the only starin the sample with an empirically determined radius (HD 209458 - fromtransit photometry) indicates excellent agreement.
| Statistical properties of exoplanets. I. The period distribution: Constraints for the migration scenario
Interesting emerging observational properties of the period-massdistribution of extra-solar planets are discussed. New recent detectionsconfirm the already emphasized lack of massive planets (m2sini >=2 MJup) on short-period orbits (P<=100 days).Furthermore, we point out i) a shortage of planets in the 10-100 dayperiod range as well as ii) a lack of light planets (m2sini<=0.75 MJup) on orbits with periods larger than ~ 100days. The latter feature is shown not to be due to small-numberstatistics with Monte-Carlo simulations. These observationalperiod-related characteristics are discussed in the context of themigration process of exoplanets. They are found to be in agreement withrecent simulations of planet interactions with viscous disks. Theobserved valley at a few tens of days in the period distribution isinterpreted as a transition region between two categories of planetsthat suffered different migration scenarios. The lack of light planetson longer-period orbits and the corresponding intriguing sharp limit inmass is tentatively explained by the runaway migration process recentlystudied by Masset & Papaloizou (2003). The observed properties alsohave implications for the observation strategies of the on-going surveysand of future higher-precision searches.
| Chemical abundances of planet-host stars. Results for alpha and Fe-group elements
In this paper, we present a study of the abundances of Si, Ca, Sc, Ti,V, Cr, Mn, Co, and Ni in a large set of stars known to harbor giantplanets, as well as in a comparison sample of stars not known to haveany planetary-mass companions. We have checked for possible chemicaldifferences between planet hosts and field stars without known planets.Our results show that overall, and for a given value of [Fe/H], theabundance trends for the planet hosts are nearly indistinguishable fromthose of the field stars. In general, the trends show nodiscontinuities, and the abundance distributions of stars with giantplanets are high [Fe/H] extensions to the curves traced by the fielddwarfs without planets. The only elements that might present slightdifferences between the two groups of stars are V, Mn, and to a lesserextent Ti and Co. We also use the available data to describe galacticchemical evolution trends for the elements studied. When comparing theresults with former studies, a few differences emerge for the high[Fe/H] tail of the distribution, a region that is sampled withunprecedented detail in our analysis.Based on observations collected at the La Silla Observatory, ESO(Chile), with the CORALIE spectrograph at the 1.2-m Euler Swisstelescope and the FEROS spectrograph at the 1.52-m ESO telescope, withthe VLT/UT2 Kueyen telescope (Paranal Observatory, ESO, Chile) using theUVES spectrograph (Observing run 67.C-0206, in service mode), with theTNG and William Herschel Telescopes, both operated at the island of LaPalma, and with the ELODIE spectrograph at the 1.93-m telescope at theObservatoire de Haute Provence.
| Statistical cataloging of archival data for luminosity class IV-V stars. II. The epoch 2001 [Fe/H] catalog
This paper describes the derivation of an updated statistical catalog ofmetallicities. The stars for which those metallicities apply are ofspectral types F, G, and K, and are on or near the main sequence. Theinput data for the catalog are values of [Fe/H] published before 2002February and derived from lines of weak and moderate strength. Theanalyses used to derive the data have been based on one-dimensional LTEmodel atmospheres. Initial adjustments which are applied to the datainclude corrections to a uniform temperature scale which is given in acompanion paper (see Taylor \cite{t02}). After correction, the data aresubjected to a statistical analysis. For each of 941 stars considered,the results of that analysis include a mean value of [Fe/H], an rmserror, an associated number of degrees of freedom, and one or moreidentification numbers for source papers. The catalog of these resultssupersedes an earlier version given by Taylor (\cite{t94b}).Catalog is only available in electronic form at the CDS via anonymousftp cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/731
| Statistical cataloging of archival data for luminosity class IV-V stars. I. The epoch 2001 temperature catalog
This paper is one of a pair in which temperatures and metallicitycatalogs for class IV-V stars are considered. The temperature catalogdescribed here is derived from a calibration based on stellar angulardiameters. If published calibrations of this kind are compared by usingcolor-index transformations, temperature-dependent differences among thecalibrations are commonly found. However, such differences are minimizedif attention is restricted to calibrations based on Johnson V-K. Acalibration of this sort from Di Benedetto (\cite{dib98}) is thereforetested and adopted. That calibration is then applied to spectroscopicand photometric data, with the latter predominating. Cousins R-Iphotometry receives special attention because of its high precision andlow metallicity sensitivity. Testing of temperatures derived from thecalibration suggests that their accuracy and precision are satisfactory,though further testing will be warranted as new results appear. Thesetemperatures appear in the catalog as values of theta equiv5040/T(effective). Most of these entries are accompanied by measured orderived values of Cousins R-I. Entries are given for 951 stars.Catalog is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/721
| Statistical properties of exoplanets. II. Metallicity, orbital parameters, and space velocities
In this article we present a detailed spectroscopic analysis of morethan 50 extra-solar planet host stars. Stellar atmospheric parametersand metallicities are derived using high resolution and high S/Nspectra. The spectroscopy results, added to the previous studies, implythat we have access to a large and uniform sample of metallicities forabout 80 planet hosts stars. We make use of this sample to confirm themetal-rich nature of stars with planets, and to show that the planetaryfrequency is rising as a function of the [Fe/H]. Furthermore, the sourceof this high metallicity is shown to have most probably a ``primordial''source, confirming previous results. The comparison of the orbitalproperties (period and eccentricity) and minimum masses of the planetswith the stellar properties also reveal some emerging but still notsignificant trends. These are discussed and some explanations areproposed. Finally, we show that the planet host stars included in theCORALIE survey have similar kinematical properties as the whole CORALIEvolume-limited planet search sample. Planet hosts simply seem to occupythe metal-rich envelope of this latter population.Based on observations collected at the La Silla Observatory, ESO(Chile), with the CORALIE spectrograph at the 1.2-m Euler Swisstelescope and the FEROS spectrograph at the 1.52-m ESO telescope, withthe VLT/UT2 Kueyen telescope (Paranal Observatory, ESO, Chile) using theUVES spectrograph (Observing run 67.C-0206, in service mode), with theTNG and William Herschel Telescopes, both operated at the island of LaPalma, and with the ELODIE spectrograph at the 1.93-m telescope at theObservatoire de Haute Provence.}
| The Puzzles of Planethood
Not Available
| On the Nature of Stars with Planets
We consider the metallicities and kinematics of nearby stars known tohave planetary-mass companions in the general context of the overallproperties of the local Galactic disk. We have used Strömgrenphotometry to determine abundances both for the extrasolar planet hoststars and for a volume-limited sample of 486 F, G, and K stars selectedfrom the Hipparcos Catalogue. The latter data show that the Sun liesnear the modal abundance of the disk, with over 45% of local starshaving supersolar metallicities. Twenty of the local stars (4.1%) areknown to have planetary-mass companions. Using that ratio to scale datafor the complete sample of planetary host stars, we find that thefraction of stars with extrasolar planets rises sharply with increasingabundance, confirming previous results. However, the frequency remainsat the 3%-4% level for stars within +/-0.15 dex of solar abundance andfalls to ~1% only for stars with abundances less than one-half solar.Given the present observational constraints, both in velocity precisionand in the available time baseline, these numbers represent a lowerlimit to the frequency of extrasolar planetary systems. A comparisonbetween the kinematics of the planetary host stars and a representativesample of disk stars suggests that the former have an average age thatis ~60% of the latter.
| Planet Host Stars: Mass, Age and Kinematics
We determine the mass, age and kinematics of 51 extra-solar planet hoststars. The results are then used to search for signs of connection ofthe data with metallicity and to investigate the population nature. Wefind that the increase in mean metallicity with stellar mass is similarto that in normal field stars, so it seems unsuitable to use thisrelation as a constraint on the theory of planet formation. The age andkinematic distributions seem to favour the metallicity of extra-solarplanet host stars being initial. Although the kinematic data of thesestars indicate their origin from two populations -- the thin and thethick disks, kinematics may not help in the maintenance of the planetaround the host. Stars with planets, brown dwarfs or stellar companionsare sorted into three groups and re-investigated separately for theirformation mechanism. The main results indicate that stars withM2 < 25 MJ have [Fe/H] > -0.1 and a wideperiod range, but there are no other differences. Thus, there does notseem to be any physically distinguishable characteristics among thethree star groups.
| The CORALIE survey for southern extra-solar planets. IX. A 1.3-day period brown dwarf disguised as a planet
In this article we present the case of HD 41004 AB, a system composed ofa K0V star and a 3.7-mag fainter M-dwarf companion. We have obtained 86CORALIE spectra of this system with the goal of obtaining preciseradial-velocity measurements. Since HD 41004 A and B are separated byonly 0.5\arcsec, in every spectrum taken for the radial-velocitymeasurement, we are observing the blended spectra of the two stars. Ananalysis of the measurements has revealed a velocity variation with anamplitude of about 50 m s-1 and a periodicity of 1.3 days.This radial-velocity signal is consistent with the expected variationinduced by the presence of a companion to either HD 41004 A or HD 41004B, or to some other effect due to e.g. activity related phenomena. Inparticular, such a small velocity amplitude could be the signature ofthe presence of a very low mass giant planetary companion to HD 41004 A,whose light dominates the spectra. The radial-velocity measurements werethen complemented with a photometric campaign and with the analysis ofthe bisector of the CORALIE Cross-Correlation Function (CCF). While theformer revealed no significant variations within the observationalprecision of ~ 0.003-0.004 mag (except for an observed flare event), thebisector analysis showed that the line profiles are varying in phasewith the radial-velocity. This latter result, complemented with a seriesof simulations, has shown that we can explain the observations byconsidering that HD 41004 B has a brown-dwarf companion orbiting withthe observed 1.3-day period. As the spectrum of the fainter HD 41004 B``moves'' relative to the one of HD 41004 A (with an amplitude of a fewkm s-1), the relative position of the spectral lines of thetwo spectra changes, thus changing the blended line-profiles. Thisvariation is large enough to explain the observed radial-velocity andbisector variations, and is compatible with the absence of anyphotometric signal. If confirmed, this detection represents the firstdiscovery of a brown dwarf in a very short period (1.3-day) orbit aroundan M dwarf. Finally, this case should be taken as a serious warningabout the importance of analyzing the bisector when looking for planetsusing radial-velocity techniques. Based on observations collected at theLa Silla Observatory, ESO (Chile), with the CORALIE spectrograph at the1.2-m Euler Swiss telescope and with the Strömgren AutomaticTelescope (SAT).
| The CORALIE survey for southern extra-solar planets. VIII. The very low-mass companions of HD 141937, HD 162020, HD 168443 and HD 202206: Brown dwarfs or ``superplanets''?
Doppler CORALIE measurements of the solar-type stars HD141937, HD 162020, HD168443 and HD 202206 show Keplerianradial-velocity variations revealing the presence of 4 new companionswith minimum masses close to the planet/brown-dwarf transition, namelywith m2sin i= 9.7, 14.4, 16.9, and 17.5 MJup,respectively. The orbits present fairly large eccentricities (0.22<=e <= 0.43). Except for HD 162020, the parent starsare metal rich compared to the Sun, as are most of the detectedextra-solar planet hosts. Considerations of tidal dissipation in theshort-period HD 162020 system points towards abrown-dwarf nature for the low-mass companion. HD168443 is a multiple system with two low-mass companions beingeither brown dwarfs or formed simultaneously in the protoplanetary disksas superplanets. For HD 202206, the radial velocitiesshow an additional drift revealing a further outer companion, the natureof which is still unknown. Finally, the stellar-host and orbitalproperties of massive planets are examined in comparison to lighterexoplanets. Observed trends include the need of metal-rich stars to formmassive exoplanets and the lack of short periods for massive planets. Ifconfirmed with improved statistics, these features may provideconstraints for the migration scenario. Based on observations collectedwith the CORALIE echelle spectrograph on the 1.2-m Euler Swiss telescopeat La Silla Observatory, ESO Chile.
| The theory of brown dwarfs and extrasolar giant planets
Straddling the traditional realms of the planets and the stars, objectsbelow the edge of the main sequence have such unique properties, and arebeing discovered in such quantities, that one can rightly claim that anew field at the interface of planetary science and astronomy is beingborn. This article extends the previous review of Burrows and Liebert(1993) and describes the essential elements of the theory of browndwarfs and giant planets. It discusses their evolution, atmosphericcomposition, and spectra, including the new spectroscopic classes L andT. Particular topics which are important for an understanding of thespectral properties include the effects of condensates, clouds,molecular abundances, and atomic opacities. Moreover, it discusses thedistinctive features of these extrasolar giant planets that areirradiated by a central primary, in particular, their reflectionspectra, albedos, and transits. Overall, the theory explains the basicsystematics of substellar-mass objects over three orders of magnitude inmass and age, and a factor of 30 in temperature.
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Osservazione e dati astrometrici
| Costellazione: | Scorpione |
| Ascensione retta: | 17h50m38.35s |
| Declinazione: | -40°19'06.1" |
| Magnitudine apparente: | 9.124 |
| Distanza: | 31.26 parsec |
| Moto proprio RA: | 20.8 |
| Moto proprio Dec: | -25.8 |
| B-T magnitude: | 10.367 |
| V-T magnitude: | 9.227 |
Cataloghi e designazioni:
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INHABITED SKY
