Contents
Images
Upload your image
DSS Images Other Images
Related articles
The impact of stellar duplicity on planet occurrence and properties. I. Observational results of a VLT/NACO search for stellar companions to 130 nearby stars with and without planets
Context: Although it is commonly agreed that the presence of a closestellar companion is likely to affect planet formation and evolution,the precise effects and their actual impact on planet occurrence arestill debated. Different conclusions have been reached on thetheoretical side, while observational constraints are sparse, aconsequence of the discrimination against close binaries in Dopplerplanet searches. Accordingly, basic questions such as how hospitablebinaries are to planets and how binary separation and mass ratio impacton planet formation, remain poorly known. Aims: In an effort to bringobservational constraints on the occurrence and properties of planets inbinaries and multiple stars, we have been conducting a dedicatedinvestigation, the results of which will be presented in this series. Methods: Our investigation follows two different approaches, one basedon radial-velocity monitoring, the other based on direct imaging. Inthis first paper, we present the observational results from oursystematic adaptive optics search with VLT/NACO for close stellarcompanions to 130 nearby stars, 57 with planets and 73 without, forcomparison. The inclusion of a control sub-sample is a unique feature ofour program that will enable a meaningful and rigorous comparisonbetween the properties of planet-host stars and the properties of fieldstars subject to the same selection effects against close binaries, butshowing no evidence for planetary companions. Results: Our data reveal95 companion candidates found in the vicinity of 33 of our targets.Nineteen of these candidates are true companions and 2 are likely boundobjects. Among planet-host stars, we discovered a tight pair of very lowmass companions to HD 65216 (projected separation of 255 AU), an early Mcompanion to HD 177830 (projected separation of 97 AU), and we resolvedthe previously known companion to HD 196050 into a close pair of Mdwarfs. Our data additionally confirm the bound nature of the companionsto HD 142, HD 16141, and HD 46375. Among control stars, we detected truecompanions to HD 7895, HD 24331, HD 31412, HD 40397, HD 43834, HD 70923,HD 78351, HD 104263, HD 129642, HD 154682, and HD 223913, and likelybound companions to HD 82241 and HD 134180. Most of these objects are Mdwarfs and have projected separations between 7 and 505 AU.Based on observations collected at the ESO VLT Yepun telescope,proposals 70.C-0557, 71.C-0125, 73.C-0124, 74.C-0048, 75.C-0069, and76.C-0057. Tables 1, 2, and Figs. 3, 4 are only available in electronicform at http://www.aanda.org
| Parent stars of extrasolar planets - VIII. Chemical abundances for 18 elements in 31 stars
We present the results of detailed spectroscopic abundance analyses for18 elements in 31 nearby stars with planets (SWPs). The resultingabundances are combined with other similar studies of nearby SWPs andcompared to a sample of nearby stars without detected planets. We findsome evidence for abundance differences between these two samples forAl, Si and Ti. Some of our results are in conflict with a recent studyof SWPs in the SPOCS data base. We encourage continued study of theabundance patterns of SWPs to resolve these discrepancies.
| Planetary Formation Scenarios Revisited: Core-Accretion versus Disk Instability
The core-accretion and disk instability models have so far been used toexplain planetary formation. These models have different conditions,such as planet mass, disk mass, and metallicity for formation of gasgiants. The core-accretion model has a metallicity condition([Fe/H]>-1.17 in the case of G-type stars), and the mass of planetsformed is less than 6 times that of the Jupiter mass MJ. Onthe other hand, the disk instability model does not have the metallicitycondition, but requires the disk to be 15 times more massive than theminimum mass solar nebulae model. The mass of planets formed is morethan 2 MJ. These results are compared to the 161 detectedplanets for each spectral type of the central stars. The results showthat 90% of the detected planets are consistent with the core-accretionmodel regardless of the spectral type. The remaining 10% are not in theregion explained by the core-accretion model, but are explained by thedisk instability model. We derived the metallicity dependence of theformation probability of gas giants for the core-accretion model.Comparing the result with the observed fraction having gas giants, theyare found to be consistent. On the other hand, the observation cannot beexplained by the disk instability model, because the condition for gasgiant formation is independent of the metallicity. Consequently, most ofplanets detected so far are thought to have been formed by thecore-accretion process, and the rest by the disk instability process.
| Are Debris Disks and Massive Planets Correlated?
Using data from the Spitzer Space Telescope Legacy Science ProgramFormation and Evolution of Planetary Systems (FEPS), we have searchedfor debris disks around nine FGK stars (2-10 Gyr), known from radialvelocity (RV) studies to have one or more massive planets. Only one ofthe sources, HD 38529, has excess emission above the stellarphotosphere; at 70 μm the signal-to-noise ratio in the excess is 4.7,while at λ<30 μm there is no evidence of excess. Theremaining sources show no excesses at any Spitzer wavelengths. Applyingsurvival tests to the FEPS sample and the results for the FGK surveyrecently published in Bryden et al., we do not find a significantcorrelation between the frequency and properties of debris disks and thepresence of close-in planets. We discuss possible reasons for the lackof a correlation.
| Celestial Exoplanet Survey Occulter: A Concept for Direct Imaging of Extrasolar Earth-like Planets from the Ground
We present a new concept for detecting and characterizing extrasolarplanets down to Earth size or smaller through direct imaging. The NewWorlds Observer (NWO) occulter developed by Cash and coworkers is placedin a particular geometrical setup in which fuel requirements are smalland the occulter is used in combination with ground-based telescopes,presumably leading to an extreme cost efficiency compared to otherconcepts with similar science goals. We investigate the various aspectsof the given geometry, such as the dynamics and radiation environment ofthe occulter, and construct a detailed example target list to ensurethat an excellent science case can be maintained despite the limited skycoverage. It is found that more than 200 systems can be observed withtwo to three visits per system, using only a few tons of fuel. For eachsystem, an Earth-sized planet with an Earth-like albedo can be found inthe habitable zone in less than 2 hr.
| Stable satellites around extrasolar giant planets
In this work, we study the stability of hypothetical satellites ofextrasolar planets. Through numerical simulations of the restrictedelliptic three-body problem we found the borders of the stable regionsaround the secondary body. From the empirical results, we derivedanalytical expressions of the critical semimajor axis beyond which thesatellites would not remain stable. The expressions are given as afunction of the eccentricities of the planet, eP, and of thesatellite, esat. In the case of prograde satellites, thecritical semimajor axis, in the units of Hill's radius, is given byaE ~ 0.4895 (1.0000 - 1.0305eP -0.2738esat). In the case of retrograde satellites, it isgiven by aE ~ 0.9309 (1.0000 - 1.0764eP -0.9812esat). We also computed the satellite stability region(aE) for a set of extrasolar planets. The results indicatethat extrasolar planets in the habitable zone could harbour theEarth-like satellites.
| 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.
| Probing long-period companions to planetary hosts. VLT and CFHT near infrared coronographic imaging surveys
Aims.We present the results of a deep imaging survey of stars surroundedby planets detected with the radial velocity technique. The purpose isto search for and to characterize long-period stellar and substellarcompanions. The sample contains a total of 26 stars, among which 6exhibit additional radial velocity drifts. Methods: .We usedNACO, at the ESO Very Large Telescope, and PUEO-KIR, at the CandianFrench Hawaiian Telescope, to conduct a near-infrared coronographicsurvey with adaptive optics of the faint circumstellar environment ofthe planetary hosts. The domain investigated ranges between 0.1'' to15'' (i.e. about 3 to 500 AU, according to the mean distance of thesample). The survey is sensitive to companions within the stellar andthe substellar domains, depending on the distance to the central starsand on the star properties. Results: .The images of 14 stars donot reveal any companions once the field objects are removed. 8 starshave close potential companions that need to be re-observed within 1-2years to check for physical companionship. 4 stars are surrounded byfaint objects which are confirmed or very probable companions. Thecompanion to HD 13445 (Gl 86) is already known. The HD 196885 star is anew close visual binary system with a high probability of being bound.The 2 newly discovered companions, HD 1237 B and HD 27442 B, sharecommon proper motions with the central stars. Orbital motion is detectedfor HD 1237 B. HD 1237 B is likely a low-mass M star, located at 70 AU(projected distance) from the primary. HD 27442 B is most probably awhite dwarf companion located at about 240 AU (projected distance).
| 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.
| Dwarfs in the Local Region
We present lithium, carbon, and oxygen abundance data for a sample ofnearby dwarfs-a total of 216 stars-including samples within 15 pc of theSun, as well as a sample of local close giant planet (CGP) hosts (55stars) and comparison stars. The spectroscopic data for this work have aresolution of R~60,000, a signal-to-noise ratio >150, and spectralcoverage from 475 to 685 nm. We have redetermined parameters and derivedadditional abundances (Z>10) for the CGP host and comparison samples.From our abundances for elements with Z>6 we determine the meanabundance of all elements in the CGP hosts to range from 0.1 to 0.2 dexhigher than nonhosts. However, when relative abundances ([x/Fe]) areconsidered we detect no differences in the samples. We find nodifference in the lithium contents of the hosts versus the nonhosts. Theplanet hosts appear to be the metal-rich extension of local regionabundances, and overall trends in the abundances are dominated byGalactic chemical evolution. A consideration of the kinematics of thesample shows that the planet hosts are spread through velocity space;they are not exclusively stars of the thin disk.
| A search for wide visual companions of exoplanet host stars: The Calar Alto Survey
We have carried out a search for co-moving stellar and substellarcompanions around 18 exoplanet host stars with the infrared camera MAGICat the 2.2 m Calar Alto telescope, by comparing our images with imagesfrom the all sky surveys 2MASS, POSS I and II. Four stars of the samplenamely HD 80606, 55 Cnc, HD 46375 and BD-10°3166, arelisted as binaries in the Washington Visual Double Star Catalogue (WDS).The binary nature of HD 80606, 55 Cnc, and HD 46375 is confirmed withboth astrometry as well as photometry, thereby the proper motion of thecompanion of HD 46375 was determined here for the first time. We derivedthe companion masses as well as the longterm stability regions foradditional companions in these three binary systems. We can rule outfurther stellar companions around all stars in the sample with projectedseparations between 270 AU and 2500 AU, being sensitive to substellarcompanions with masses down to 60 {MJup} (S/N=3).Furthermore we present evidence that the two components of the WDSbinary BD-10°3166 are unrelated stars, i.e this system isa visual pair. The spectrophotometric distance of the primary (a K0dwarf) is 67 pc, whereas the presumable secondaryBD-10°3166 B (a M4 to M5 dwarf) is located at a distanceof 13 pc in the foreground.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| 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.
| 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.
| A Comparative Study on Lithium Abundances in Solar-Type Stars With and Without Planets
We have investigated the abundance anomalies of lithium for stars withplanets in the temperature range of 5600-5900 K reported by Israelianand coworkers, as compared to 20 normal stars in the same temperatureand metallicity ranges. Our result indicates a higher probability oflithium depletion for stars with planets in the main-sequence stage. Itseems that stellar photospheric abundances of lithium in stars withplanets may be somewhat affected by the presence of planets. Twopossible mechanisms are considered to account for the lower Liabundances of stars with planets. One is related to the rotation-inducedmixing due to the conservation of angular momentum by the protoplanetarydisk, and the other is a shear instability triggered by planetmigration. These results provide new information on stellar evolutionand the lithium evolution of the Galaxy.
| Oxygen abundances in planet-harbouring stars. Comparison of different abundance indicators
We present a detailed and uniform study of oxygen abundances in 155solar type stars, 96 of which are planet hosts and 59 of which form partof a volume-limited comparison sample with no known planets. EWmeasurements were carried out for the [O I] 6300 Å line and the OI triplet, and spectral synthesis was performed for several OH lines.NLTE corrections were calculated and applied to the LTE abundanceresults derived from the O I 7771-5 Å triplet. Abundances from [OI], the O I triplet and near-UV OH were obtained in 103, 87 and 77dwarfs, respectively. We present the first detailed and uniformcomparison of these three oxygen indicators in a large sample ofsolar-type stars. There is good agreement between the [O/H] ratios fromforbidden and OH lines, while the NLTE triplet shows a systematicallylower abundance. We found that discrepancies between OH, [O I] and the OI triplet do not exceed 0.2 dex in most cases. We have studied abundancetrends in planet host and comparison sample stars, and no obviousanomalies related to the presence of planets have been detected. Allthree indicators show that, on average, [O/Fe] decreases with [Fe/H] inthe metallicity range -0.8< [Fe/H] < 0.5. The planet host starspresent an average oxygen overabundance of 0.1-0.2 dex with respect tothe comparison sample.
| Synthetic Lick Indices and Detection of α-enhanced Stars. III. F, G, and K Stars with [Fe/H] > 0.00
A sample of 119 F, G, and K solar neighborhood stars, selected under thecondition [Fe/H]>0.00, is investigated in order to detect which ofthem, if any, present α-enhanced characteristics. According to thekinematics, the sample represents stars of the thin-disk component ofthe Galaxy. The search of α-enhanced characteristics is performedby adopting an already tested procedure that does not require previousknowledge of the stellar main atmospheric parameters. The analysis isbased on the comparison of spectral indices in the Lick IDS system,coming from different observational data sets, with synthetic onescomputed with solar-scaled abundances and with α-elementenhancement. The main result of the analysis is the extreme paucity(likely just one in 119) of α-enhanced stars in our sample, thussuggesting [α/Fe]=0.0 for thin-disk stars with [Fe/H]>0.00.This result, which is in agreement with the standard evolutionarypicture of the disk of the Galaxy, is compared with recent results fromhigh-resolution analysis reported in the literature. The role of theatmospheric parameter assumptions in the analysis of high-resolutionspectroscopic data is discussed, and a possible explanation ofdiscrepant results about α-enhancement for stars with[Fe/H]>0.00 is presented.
| A link between the semimajor axis of extrasolar gas giant planets and stellar metallicity
The fact that most extrasolar planets found to date are orbitingmetal-rich stars lends credence to the core accretion mechanism of gasgiant planet formation over its competitor, the disc instabilitymechanism. However, the core accretion mechanism is not refined to thepoint of explaining orbital parameters such as the unexpected semimajoraxes and eccentricities. We propose a model that correlates themetallicity of the host star with the original semimajor axis of itsmost massive planet, prior to migration, assuming that the coreaccretion scenario governs giant gas planet formation. The modelpredicts that the optimum regions for planetary formation shift inwardsas stellar metallicity decreases, providing an explanation for theobserved absence of long-period planets in metal-poor stars. We compareour predictions with the available data on extrasolar planets for starswith masses similar to the mass of the Sun. A fitting procedure producesan estimate of what we define as the zero-age planetary orbit (ZAPO)curve as a function of the metallicity of the star. The model hints thatthe lack of planets circling metal-poor stars may be partly caused by anenhanced destruction probability during the migration process, becausethe planets lie initially closer to their central star.
| 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.
| Sulphur abundance in Galactic stars
We investigate sulphur abundance in 74 Galactic stars by using highresolution spectra obtained at ESO VLT and NTT telescopes. For the firsttime the abundances are derived, where possible, from three opticalmultiplets: Mult. 1, 6, and 8. By combining our own measurements withdata in the literature we assemble a sample of 253 stars in themetallicity range -3.2 [Fe/H] +0.5. Two important features,which could hardly be detected in smaller samples, are obvious from thislarge sample: 1) a sizeable scatter in [S/Fe] ratios around [Fe/H]-1; 2) at low metallicities we observe stars with [S/Fe] 0.4, aswell as stars with higher [S/Fe] ratios. The latter do not seem to bekinematically different from the former ones. Whether the latter findingstems from a distinct population of metal-poor stars or simply from anincreased scatter in sulphur abundances remains an open question.
| Kinematics, ages and metallicities for F- and G-type stars in the solar neighbourhood
A new metallicity distribution and an age-metallicity relation arepresented for 437 nearby F and G turn-off and sub-giant stars selectedfrom radial velocity data of Nidever et al. Photometric metallicitiesare derived from uvby- Hβ photometry, and the stellar ages from theisochrones of Bergbusch & VandenBerg as transformed to uvbyphotometry using the methods of Clem et al.The X (stellar population) criterion of Schuster et al., which combinesboth kinematic and metallicity information, provides 22 thick-discstars. σW= 32 +/- 5 km s-1,= 154 +/- 6 km s-1 and<[M/H]>=-0.55 +/- 0.03 dex for these thick-disc stars, which is inagreement with values from previous studies of the thick disc.α-element abundances which are available for some of thesethick-disc stars show the typical α-element signatures of thethick disc, supporting the classification procedure based on the Xcriterion.Both the scatter in metallicity at a given age and the presence of old,metal-rich stars in the age-metallicity relation make it difficult todecide whether or not an age-metallicity relation exists for the olderthin-disc stars. For ages greater than 3 Gyr, our results agree with theother recent studies that there is almost no correlation between age andmetallicity, Δ([M/Fe])/Δ(age) =-0.01 +/- 0.005 dexGyr-1. For the 22 thick-disc stars there is a range in agesof 7-8 Gyr, but again almost no correlation between age and metallicity.For the subset of main-sequence stars with extra-solar planets, theage-metallicity relation is very similar to that of the total sample,very flat, the main difference being that these stars are mostlymetal-rich, [M/H]>~-0.2 dex. However, two of these stars have[M/H]~-0.6 dex and have been classified as thick-disc stars. As for thetotal sample, the range in ages for these stars with extra-solarplanetary systems is considerable with a nearly uniform distributionover 3 <~ age <~ 13 Gyr.
| 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.
| 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.
| 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.
| The Effective Temperature Scale of FGK Stars. I. Determination of Temperatures and Angular Diameters with the Infrared Flux Method
The infrared flux method (IRFM) has been applied to a sample of 135dwarf and 36 giant stars covering the following regions of theatmospheric parameter space: (1) the metal-rich ([Fe/H]>~0) end(consisting mostly of planet-hosting stars), (2) the cool(Teff<~5000 K) metal-poor (-1<~[Fe/H]<~-3) dwarfregion, and (3) the very metal-poor ([Fe/H]<~-2.5) end. These starswere especially selected to cover gaps in previous works onTeff versus color relations, particularly the IRFMTeff scale of A. Alonso and collaborators. Our IRFMimplementation was largely based on the Alonso et al. study (absoluteinfrared flux calibration, bolometric flux calibration, etc.) with theaim of extending the ranges of applicability of their Teffversus color calibrations. In addition, in order to improve the internalaccuracy of the IRFM Teff scale, we recomputed thetemperatures of almost all stars from the Alonso et al. work usingupdated input data. The updated temperatures do not significantly differfrom the original ones, with few exceptions, leaving the Teffscale of Alonso et al. mostly unchanged. Including the stars withupdated temperatures, a large sample of 580 dwarf and 470 giant stars(in the field and in clusters), which cover the ranges3600K<~Teff<~8000K and -4.0<~[Fe/H]<~+0.5, haveTeff homogeneously determined with the IRFM. The meanuncertainty of the temperatures derived is 75 K for dwarfs and 60 K forgiants, which is about 1.3% at solar temperature and 4500 K,respectively. It is shown that the IRFM temperatures are reliable in anabsolute scale given the consistency of the angular diameters resultingfrom the IRFM with those measured by long baseline interferometry, lunaroccultation, and transit observations. Using the measured angulardiameters and bolometric fluxes, a comparison is made between IRFM anddirect temperatures, which shows excellent agreement, with the meandifference being less than 10 K for giants and about 20 K for dwarfstars (the IRFM temperatures being larger in both cases). This resultwas obtained for giants in the ranges 3800K
| 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.
| Evolution of Cold Circumstellar Dust around Solar-type Stars
We present submillimeter (Caltech Submillimeter Observatory 350 μm)and millimeter (Swedish-ESO Submillimetre Telescope [SEST] 1.2 mm, OwensValley Radio Observatory [OVRO] 3 mm) photometry for 127 solar-typestars from the Formation and Evolution of Planetary Systems SpitzerLegacy program that have masses between ~0.5 and 2.0 Msolarand ages from ~3 Myr to 3 Gyr. Continuum emission was detected towardfour stars with a signal-to-noise ratio>=3: the classical T Tauristars RX J1842.9-3532, RX J1852.3-3700, and PDS 66 with SEST, and thedebris-disk system HD 107146 with OVRO. RX J1842.9-3532 and RXJ1852.3-3700 are located in projection near the R CrA molecular cloud,with estimated ages of ~10 Myr (Neuhäuser et al.), whereas PDS 66is a probable member of the ~20 Myr old Lower Centaurus-Crux subgroup ofthe Scorpius-Centaurus OB association (Mamajek et al.). The continuumemission toward these three sources is unresolved at the 24" SESTresolution and likely originates from circumstellar accretion disks,each with estimated dust masses of ~5×10-5Msolar. Analysis of the visibility data toward HD 107146(age~80-200 Myr) indicates that the 3 mm continuum emission is centeredon the star within the astrometric uncertainties and resolved with aGaussian-fit FWHM size of (6.5"+/-1.4")×(4.2"+/-1.3"), or185AU×120 AU. The results from our continuum survey are combinedwith published observations to quantify the evolution of dust mass withtime by comparing the mass distributions for samples with differentstellar ages. The frequency distribution of circumstellar dust massesaround solar-type stars in the Taurus molecular cloud (age~2 Myr) isdistinguished from that around 3-10 Myr and 10-30 Myr old stars at asignificance level of ~1.5 and ~3 σ, respectively. These resultssuggest a decrease in the mass of dust contained in small dust grainsand/or changes in the grain properties by stellar ages of 10-30 Myr,consistent with previous conclusions. Further observations are needed todetermine if the evolution in the amount of cold dust occurs on evenshorter timescales.
| Are beryllium abundances anomalous in stars with giant planets?
In this paper we present beryllium (Be) abundances in a large sample of41 extra-solar planet host stars, and for 29 stars without any knownplanetary-mass companion, spanning a large range of effectivetemperatures. The Be abundances were derived through spectral synthesisdone in standard Local Thermodynamic Equilibrium, using spectra obtainedwith various instruments. The results seem to confirm that overall,planet-host stars have ``normal'' Be abundances, although a small, butnot significant, difference might be present. This result is discussed,and we show that this difference is probably not due to any stellar``pollution'' events. In other words, our results support the idea thatthe high-metal content of planet-host stars has, overall, a``primordial'' origin. However, we also find a small subset ofplanet-host late-F and early-G dwarfs that might have higher thanaverage Be abundances. The reason for the offset is not clear, and mightbe related either to the engulfment of planetary material, to galacticchemical evolution effects, or to stellar-mass differences for stars ofsimilar temperature.Based on observations collected with the VLT/UT2 Kueyen telescope(Paranal Observatory, ESO, Chile) using the UVES spectrograph (Observingruns 66.C-0116 A, 66.D-0284 A, and 68.C-0058 A), and with the WilliamHerschel and Nordic Optical Telescopes, operated on the island of LaPalma by the Isaac Newton Group and jointly by Denmark, Finland,Iceland, and Norway, respectively, in the Spanish Observatorio del Roquede los Muchachos of the Instituto de Astrofísica de Canarias.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Sextans |
| Right ascension: | 10h42m48.53s |
| Declination: | -02°11'01.5" |
| Apparent magnitude: | 7.308 |
| Distance: | 32.321 parsecs |
| Proper motion RA: | -11.8 |
| Proper motion Dec: | -223.8 |
| B-T magnitude: | 8.175 |
| V-T magnitude: | 7.38 |
Catalogs and designations:
|
INHABITED SKY
