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The Frequency of Low-mass Exoplanets. III. Toward ?? at Short Periods
Determining the occurrence rate of "super-Earth" planets (m sin i <10 M ?) is a critically important step on the pathtoward determining the frequency of Earth-like planets(??), and hence the uniqueness of our solar system.Current radial-velocity surveys, achieving precisions of 1 ms-1, are now able to detect super-Earths and providemeaningful estimates of their occurrence rate. We present an analysis of67 solar-type stars from the Anglo-Australian Planet Search specificallytargeted for very high precision observations. When corrected forincompleteness, we find that the planet occurrence rate increasessharply with decreasing planetary mass. Our results are consistent withthose from other surveys: in periods shorter than 50 days, we find that3.0% of stars host a giant (msin i > 100 M ?)planet, and that 17.4% of stars host a planet with msin i < 10 M?. The preponderance of low-mass planets inshort-period orbits is in conflict with formation simulations in whichthe majority of super-Earths reside at larger orbital distances. Thiswork gives a hint as to the size of ??, but to makemeaningful predictions on the frequency of terrestrial planets inlonger, potentially habitable orbits, low-mass terrestrial planetsearches at periods of 100-200 days must be made an urgent priority forground-based Doppler planet searches in the years ahead.
| Beryllium abundances in stars with planets. Extending the sample
Context. Chemical abundances of light elements such as beryllium inplanet-host stars allow us to study the planet formation scenariosand/or investigate possible surface pollution processes. Aims: Wepresent here an extension of previous beryllium abundance studies. Thecomplete sample consists of 70 stars that host planets and 30 starswithout known planetary companions. The aim of this paper is to furtherassess the trends found in previous studies with fewer objects. Thiswill provide more information on the processes of depletion and mixingof light elements in the interior of late-type stars, and will providepossible explanations for the abundance differences between stars thathost planets and "single" stars. Methods: Using high-resolutionUVES spectra, we measure beryllium abundances of 26 stars that hostplanets and one "single" star mainly using the ? 3131.065 ÅBe ii line, by fitting synthetic spectra to the observational data. Wealso compile beryllium abundance measurements of 44 stars hostingplanets and 29 "single" stars from the literature, resulting in a finalsample of 100 objects. Results: We confirm that the berylliumcontent is roughly the same in stars hosting planets and in "single"stars at temperatures Teff ? 5700 K. The sample is stillsmall for Teff ? 5500 K, but it seems that the scatterin Be abundances of dwarf stars is slightly higher at these coolertemperatures. Conclusions: We search for distinctivecharacteristics of planet hosts through correlations of Be abundanceversus Li abundance, age, metallicity, and oxygen abundance. These couldprovide some insight into the formation and evolution of planetarysystems, but we did not find any clear correlation.Based on observations obtained with UVES at VLT Kueyen 8.2 m telescopein programme 074.C-0134(A).
| The NASA-UC Eta-Earth Program. III. A Super-Earth Orbiting HD 97658 and a Neptune-mass Planet Orbiting Gl 785
We report the discovery of planets orbiting two bright, nearby early Kdwarf stars, HD 97658 and Gl 785. These planets were detected byKeplerian modeling of radial velocities measured with Keck-HIRES for theNASA-UC Eta-Earth Survey. HD 97658 b is a close-in super-Earth withminimum mass Msin i = 8.2 ± 1.2 M ?, orbitalperiod P = 9.494 ± 0.005 days, and an orbit that is consistentwith circular. Gl 785 b is a Neptune-mass planet with Msin i = 21.6± 2.0 M ?, P = 74.39 ± 0.12 days, andorbital eccentricity e = 0.30 ± 0.09. Photometric observationswith the T12 0.8 m automatic photometric telescope at FairbornObservatory show that HD 97658 is photometrically constant at the radialvelocity period to 0.09 mmag, supporting the existence of the planet.Based on observations obtained at the W. M. Keck Observatory, which isoperated jointly by the University of California and the CaliforniaInstitute of Technology. Keck time has been granted by both NASA and theUniversity of California.
| Measuring Be Depletion in Cool Stars with Exoplanets
We present new UVES spectra of a sample of 14 mostly cool unevolvedstars with planetary companions with the aim of studying possibledifferences in Be abundance with respect to stars without detectedplanets. We determine Be abundances for these stars that show anincrease in Be depletion as we move to lower temperatures. We carry outa differential analysis of spectra of analog stars with and withoutplanets to establish a possible difference in Be content. While for hotstars no measurable difference is found in Be, for the only cool (Teff~ 5000 K) planet-host star with several analogs in thesample we find enhanced Be depletion by 0.25 dex. This is a firstindication that the extra-depletion of Li in solar-type stars withplanets may also happen for Be, but shifted toward lower temperatures (Teff < 5500 K) due to the depth of the convectiveenvelopes. The processes that take place in the formation of planetarysystems may affect the mixing of material inside their host stars andhence the abundances of light elements.Based on observations made with UVES at VLT Kueyen 8.2 m telescope atthe European Southern Observatory (Cerro Paranal, Chile) in program75.D-0453A.
| On the Frequency of Jupiter Analogs
The Anglo-Australian Planet Search has now accumulated 12 years ofradial-velocity data with long-term instrumental precision better than 3m s-1. In this paper, we expand on earlier simulation work,to probe the frequency of near-circular, long-period gas-giant planetsresiding at orbital distances of 3-6 AU—the so-called Jupiteranalogs. We present the first comprehensive analysis of the frequency ofthese objects based on radial-velocity data. We find that 3.3% of starsin our sample host Jupiter analogs; detailed, star-by-star simulationsshow that no more than 37% of stars host a giant planet between 3 and 6AU.
| The Spitzer Atlas of Stellar Spectra (SASS)
We present the Spitzer Atlas of Stellar Spectra, which includes 159stellar spectra (5-32 ?m R ~ 100) taken with the InfraredSpectrograph on the Spitzer Space Telescope. This Atlas gathersrepresentative spectra of a broad section of the Hertzsprung-Russelldiagram, intended to serve as a general stellar spectral reference inthe mid-infrared. It includes stars from all luminosity classes, as wellas Wolf-Rayet (WR) objects. Furthermore, it includes some objects ofintrinsic interest, such as blue stragglers and certain pulsatingvariables. All of the spectra have been uniformly reduced, and all areavailable online. For dwarfs and giants, the spectra of early-typeobjects are relatively featureless, characterized by the presence ofhydrogen lines in A spectral types. Besides these, the most noticeablephotospheric features correspond to water vapor and silicon monoxide inlate-type objects and methane and ammonia features at the latestspectral types. Most supergiant spectra in the Atlas present evidence ofcircumstellar gas and/or dust. The sample includes five M supergiantspectra, which show strong dust excesses and in some cases polycyclicaromatic hydrocarbon features. Sequences of WR stars present thewell-known pattern of lines of He I and He II, as well as forbiddenlines of ionized metals. The characteristic flat-top shape of the [NeIII] line is evident even at these low spectral resolutions. SeveralLuminous Blue Variables and other transition stars are present in theAtlas and show very diverse spectra, dominated by circumstellar gas anddust features. We show that the [8]-[24] Spitzer colors (IRAC and MIPS)are poor predictors of spectral type for most luminosity classes.
| The Occurrence and Mass Distribution of Close-in Super-Earths, Neptunes, and Jupiters
The questions of how planets form and how common Earth-like planets arecan be addressed by measuring the distribution of exoplanet masses andorbital periods. We report the occurrence rate of close-in planets (withorbital periods less than 50 days), based on precise Dopplermeasurements of 166 Sun-like stars. We measured increasing planetoccurrence with decreasing planet mass (M). Extrapolation of a power-lawmass distribution fitted to our measurements, df/dlogM = 0.39M-0.48, predicts that 23% of stars harbor a close-inEarth-mass planet (ranging from 0.5 to 2.0 Earth masses). Theoreticalmodels of planet formation predict a deficit of planets in the domainfrom 5 to 30 Earth masses and with orbital periods less than 50 days.This region of parameter space is in fact well populated, implying thatsuch models need substantial revision.
| A High-Contrast Imaging Survey of SIM Lite Planet Search Targets
With the development of extreme high contrast ground-based adaptiveoptics instruments and space missions aimed at detecting andcharacterizing Jupiter- and terrestrial-mass planets, it is criticalthat each target star be thoroughly vetted to determine whether it is aviable target, given both the instrumental design and scientific goalsof the program. With this in mind, we have conducted a high-contrastimaging survey of mature AFGKM stars with the PALAO/PHARO instrument onthe Palomar 200 inch telescope. The survey reached sensitivitiessufficient to detect brown dwarf companions at separations of >50 AU.The results of this survey will be utilized both by future directimaging projects such as GPI, SPHERE, and P1640 and indirect detectionmissions such as SIM Lite. Out of 84 targets, all but one have noclose-in (0.45-1") companions and 64 (76%) have no stars at all withinthe 25" field of view. The sensitivity contrasts in the Kspassband ranged from 4.5 to 10 for this set of observations. These starswere selected as the best nearby targets for habitable planet searchesbecause of their long-lived habitable zones (>1 billion years). Wereport two stars, GJ 454 and GJ 1020, with previously unpublished propermotion companions. In both cases, the companions are stellar in natureand are most likely M dwarfs based on their absolute magnitudes andcolors. Based on our mass sensitivities and level of completeness, wecan place an upper limit of ˜17% on the presence of brown dwarfcompanions with masses >40 MJ at separations of >1". Wealso discuss the importance of including statistics on those stars withno detected companions in their field of view for the sake of futurecompanion searches and an overall understanding of the population oflow-mass objects around nearby stars.
| A Survey of Stellar Families: Multiplicity of Solar-type Stars
We present the results of a comprehensive assessment of companions tosolar-type stars. A sample of 454 stars, including the Sun, was selectedfrom the Hipparcos catalog with ?>40 mas,??/? < 0.05, 0.5 <= B - V <= 1.0(~F6-K3), and constrained by absolute magnitude and color to excludeevolved stars. These criteria are equivalent to selecting all dwarf andsubdwarf stars within 25 pc with V-band flux between 0.1 and 10 timesthat of the Sun, giving us a physical basis for the term "solar-type."New observational aspects of this work include surveys for (1) veryclose companions with long-baseline interferometry at the Center forHigh Angular Resolution Astronomy Array, (2) close companions withspeckle interferometry, and (3) wide proper-motion companions identifiedby blinking multi-epoch archival images. In addition, we include theresults from extensive radial-velocity monitoring programs and evaluatecompanion information from various catalogs covering many differenttechniques. The results presented here include four new commonproper-motion companions discovered by blinking archival images.Additionally, the spectroscopic data searched reveal five new stellarcompanions. Our synthesis of results from many methods and sourcesresults in a thorough evaluation of stellar and brown dwarf companionsto nearby Sun-like stars. The overall observed fractions of single,double, triple, and higher-order systems are 56% ± 2%, 33%± 2%, 8% ± 1%, and 3% ± 1%, respectively, countingall confirmed stellar and brown dwarf companions. If all candidate,i.e., unconfirmed, companions identified are found to be real, thepercentages would change to 54% ± 2%, 34% ± 2%, 9%± 2%, and 3% ± 1%, respectively. Our completeness analysisindicates that only a few undiscovered companions remain in thiswell-studied sample, implying that the majority (54% ± 2%) ofsolar-type stars are single, in contrast to the results of priormultiplicity studies. Our sample is large enough to enable a check ofthe multiplicity dependence on various physical parameters by analyzingappropriate subsamples. Bluer, more massive stars are seen as morelikely to have companions than redder, less massive ones, consistentwith the trend seen over the entire spectral range. Systems with largerinteraction cross sections, i.e., those with more than two components orlong orbital periods, are preferentially younger, suggesting thatcompanions may be stripped over time by dynamical interactions. Weconfirm the planet-metallicity correlation (i.e., higher metallicitystars are more likely to host planets), but are unable to check it forbrown dwarfs due to the paucity of such companions, implying that thebrown dwarf desert extends over all separation regimes. We find nocorrelation between stellar companions and metallicity for B - V< 0.625, but among the redder subset, metal-poor stars ([Fe/H]<-0.3) are more likely to have companions with a 2.4?significance. The orbital-period distribution of companions is unimodaland roughly log normal with a peak and median of about 300 years. Theperiod-eccentricity relation shows the expected circularization forperiods below 12 days, caused by tidal forces over the age of theGalaxy, followed by a roughly flat distribution. The mass-ratiodistribution shows a preference for like-mass pairs, which occur morefrequently in relatively close pairs. The fraction of planet hosts amongsingle, binary, and multiple systems are statisticallyindistinguishable, suggesting that planets are as likely to form aroundsingle stars as they are around components of binary or multiple systemswith sufficiently wide separations. This, along with the preference oflong orbital periods among stellar systems, increases the space aroundstars conducive for planet formation, and perhaps life.
| Chromospheric activity and rotation of FGK stars in the solar vicinity. An estimation of the radial velocity jitter
Context. Chromospheric activity produces both photometric andspectroscopic variations that can be mistaken as planets. Large spotscrossing the stellar disc can produce planet-like periodic variations inthe light curve of a star. These spots clearly affect the spectral lineprofiles, and their perturbations alter the line centroids creating aradial velocity jitter that might “contaminate” thevariations induced by a planet. Precise chromospheric activitymeasurements are needed to estimate the activity-induced noise thatshould be expected for a given star. Aims: We obtain precisechromospheric activity measurements and projected rotational velocitiesfor nearby (d ? 25 pc) cool (spectral types F to K) stars, toestimate their expected activity-related jitter. As a complementaryobjective, we attempt to obtain relationships between fluxes indifferent activity indicator lines, that permit a transformation oftraditional activity indicators, i.e., Ca ii H & K lines, to othersthat hold noteworthy advantages. Methods: We used high resolution(~50 000) echelle optical spectra. Standard data reduction was performedusing the IRAF echelle package. To determine the chromospheric emissionof the stars in the sample, we used the spectral subtraction technique.We measured the equivalent widths of the chromospheric emission lines inthe subtracted spectrum and transformed them into fluxes by applyingempirical equivalent width and flux relationships. Rotational velocitieswere determined using the cross-correlation technique. To inferactivity-related radial velocity (RV) jitter, we used empiricalrelationships between this jitter and the R'_HK index. Results:We measured chromospheric activity, as given by different indicatorsthroughout the optical spectra, and projected rotational velocities for371 nearby cool stars. We have built empirical relationships among themost important chromospheric emission lines. Finally, we used themeasured chromospheric activity to estimate the expected RV jitter forthe active stars in the sample.Based on observations made with the 2.2 m telescope at the CentroAstronómico Hispano Alemán (CAHA) at Calar Alto (Spain)and the Telescopio Nazionale Galileo (TNG) operated on the island of LaPalma by the Istituto Nazionale de Astrofisica Italiano (INAF), in theSpanish Observatorio del Roque de los Muchachos. This research has beensupported by the Programa de Acceso a InfraestructurasCientíficas y Tecnológicas Singulares (ICTS).Tables A1 toA4 are only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/520/A79
| Explorations Beyond the Snow Line: Spitzer/IRS Spectra of Debris Disks Around Solar-type Stars
We have observed 152 nearby solar-type stars with the InfraredSpectrometer (IRS) on the Spitzer Space Telescope. Including stars thatmet our criteria but were observed in other surveys, we get an overallsuccess rate for finding excesses in the long-wavelength IRS band (30-34μm) of 11.8% ± 2.4%. The success rate for excesses in theshort-wavelength band (8.5-12 μm) is ~1% including sources from othersurveys. For stars with no excess at 8.5-12 μm, the IRS data set3σ limits of around 1000 times the level of zodiacal emissionpresent in our solar system, while at 30-34 μm data set limits ofaround 100 times the level of our solar system. Two stars (HD 40136 andHD 10647) show weak evidence for spectral features; the excess emissionin the other systems is featureless. If the emitting material consistsof large (10 μm) grains as implied by the lack of spectral features,we find that these grains are typically located at or beyond the snowline, ~1-35 AU from the host stars, with an average distance of 14± 6 AU; however, smaller grains could be located at significantlygreater distances from the host stars. These distances correspond todust temperatures in the range ~50-450 K. Several of the disks are wellmodeled by a single dust temperature, possibly indicative of a ring-likestructure. However, a single dust temperature does not match the datafor other disks in the sample, implying a distribution of temperatureswithin these disks. For most stars with excesses, we detect an excess atboth IRS and Multiband Imaging Photometer for Spitzer (MIPS)wavelengths. Only three stars in this sample show a MIPS 70 μm excesswith no IRS excess, implying that very cold dust is rare aroundsolar-type stars.
| On the Relationship Between Debris Disks and Planets
Dust in debris disks is generated by collisions among planetesimals. Theexistence of these planetesimals is a consequence of the planetformation process, but the relationship between debris disks and planetshas not been clearly established. Here we analyze Spitzer/MIPS 24 and 70μm data for 150 planet-bearing stars, and compare the incidence ofdebris disks around these stars with a sample of 118 stars around whichplanets have been searched for, but not found. Together they comprisethe largest sample ever assembled to deal with this question. The use ofsurvival analysis techniques allows us to account for the large numberof nondetections at 70 μm. We discovered 10 new debris disks aroundstars with planets and one around a star without known planets. We foundthat the incidence of debris disks is marginally higher among stars withplanets, than among those without, and that the brightness of theaverage debris disk is not significantly different in the two samples.We conclude that the presence of a planet that has been detected viacurrent radial velocity techniques is not a good predictor of thepresence of a debris disk detected at infrared wavelengths.
| The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/941
| The main sequence from F to K stars of the solar neighbourhood in SDSS colours
For an understanding of Galactic stellar populations in the SDSS filtersystem well defined stellar samples are needed. The nearby stars providea complete stellar sample representative for the thin disc population.We compare the filter transformations of different authors applied tothe main sequence stars from F to K dwarfs to SDSS filter system anddiscuss the properties of the main sequence. The location of the meanmain sequence in colour-magnitude diagrams is very sensitive tosystematic differences in the filter transformation. A comparison withfiducial sequences of star clusters observed in g', r', and i' show goodagreement. Theoretical isochrones from Padua and from Dartmouth havestill some problems, especially in the (r-i) colours.
| A catalogue of multiplicity among bright stellar systems
We consider the multiplicity of stellar systems with (combined)magnitude brighter than 6.00 in Hipparcos magnitudes. We identify 4559such bright systems (including the Sun), and the frequencies ofmultiplicities 1, 2,..., 7 are found to be 2718, 1437, 285, 86, 20, 11and 2. We discuss the uncertainties, which are substantial. We alsoconsider the distributions of periods of orbits and suborbits. We notethat for even more restricted set of 478 systems with VH<= 4.00, the proportions of higher multiples up to sextuple areprogressively larger (213, 179, 54, 19, 8, 5), suggesting substantialincompleteness in even the reasonably well studied larger sample.This sample can be seen as relatively thoroughly studied formultiplicity, and reasonably representative of stars more massive thanthe Sun. But the restriction to VH <= 6 means that oursample contains hardly any systems where all components are low-massmain-sequence stars (K or M).Data on multiplicity are important as a constraint on (i) the starformation problem, (ii) the problem of the evolution of the Galacticstellar population and (iii) the interaction of dynamics and evolutionthrough the effect of Kozai cycles. We discuss these topics briefly.
| Spectroscopic parameters for 451 stars in the HARPS GTO planet search program. Stellar [Fe/H] and the frequency of exo-Neptunes
To understand the formation and evolution of solar-type stars in thesolar neighborhood, we need to measure their stellar parameters to highaccuracy. We present a catalogue of accurate stellar parameters for 451stars that represent the HARPS Guaranteed Time Observations (GTO)“high precision” sample. Spectroscopic stellar parameterswere measured using high signal-to-noise (S/N) spectra acquired with theHARPS spectrograph. The spectroscopic analysis was completed assumingLTE with a grid of Kurucz atmosphere models and the recent ARES code formeasuring line equivalent widths. We show that our results agree wellwith those ones presented in the literature (for stars in common). Wepresent a useful calibration for the effective temperature as a functionof the index color B-V and [Fe/H]. We use our results to study themetallicity-planet correlation, namely for very low mass planets. Theresults presented here suggest that in contrast to their joviancouterparts, neptune-like planets do not form preferentially aroundmetal-rich stars. The ratio of jupiter-to-neptunes is also an increasingfunction of stellar metallicity. These results are discussed in thecontext of the core-accretion model for planet formation.Based on observations collected at La Silla Observatory, ESO, Chile,with the HARPS spectrograph at the 3.6-m telescope (072.C-0488(E)). FullTables 1 and 3 are only available in electronic form at the CDS vianonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/487/373
| Oxygen abundances in nearby stars. Clues to the formation and evolution of the Galactic disk
The abundances of iron and oxygen are homogeneously determined in asample of 523 nearby (d<150 pc) FGK disk and halo stars withmetallicities in the range -1.5<[Fe/H]<0.5. Iron abundances wereobtained from an LTE analysis of a large set of Fe I and Fe II lineswith reliable atomic data. Oxygen abundances were inferred from arestricted non-LTE analysis of the 777 nm O I triplet. We adopted theinfrared flux method temperature scale and surface gravities based onHipparcos trigonometric parallaxes. Within this framework, theionization balance of iron lines is not satisfied: the mean abundancesfrom the Fe I lines are systematically lower by 0.06 dex than those fromthe Fe II lines for dwarf stars of Teff>5500 K and[Fe/H]<0.0, and giant stars of all temperatures and metallicitiescovered by our sample. The discrepancy worsens for cooler and metal-richmain-sequence stars. We use the stellar kinematics to compute theprobabilities of our sample stars to be members of the thin disk, thickdisk, or halo of the Galaxy. We find that the majority of thekinematically-selected thick-disk stars show larger [O/Fe] ratioscompared to thin-disk stars while the rest show thin-disk abundances,which suggests that the latter are thin-disk members with unusual(hotter) kinematics. A close examination of this pattern for disk starswith ambiguous probabilities shows that an intermediate population withproperties between those of the thin and thick disks does not exist, atleast in the solar neighborhood. Excluding the stars with unusualkinematics, we find that thick-disk stars show slowly decreasing [O/Fe]ratios from about 0.5 to 0.4 in the -0.8<[Fe/H]<-0.3 range. Usinga simple model for the chemical evolution of the thick disk we show thatthis trend results directly from the metallicity dependence of the TypeII supernova yields. At [Fe/H]>-0.3, we find no obvious indication ofa sudden decrease (i.e., a "knee") in the [O/Fe] vs. [Fe/H] pattern ofthick-disk stars that would connect the thick and thin disk trends at ahigh metallicity. We conclude that Type Ia supernovae (SN Ia) did notcontribute significantly to the chemical enrichment of the thick disk.In the -0.8<[Fe/H]<+0.3 range, thin-disk stars show decreasing[O/Fe] ratios from about 0.4 to 0.0 that require a SN Ia contribution.The implications of these results for studies of the formation andevolution of the Galactic disk are discussed.Tables 4-6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/465/271 Partially based onobservations obtained with the Hobby-Eberly Telescope, which is a jointproject of the University of Texas at Austin, the Pennsylvania StateUniversity, Stanford University, Ludwig-Maximilians-UniversitätMünchen, and Georg-August-Universität Göttingen; and datafrom the UVES Paranal Observatory Project (ESO DDT Program ID266.D-5655).
| Structure and Evolution of Nearby Stars with Planets. II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog
We derive detailed theoretical models for 1074 nearby stars from theSPOCS (Spectroscopic Properties of Cool Stars) Catalog. The Californiaand Carnegie Planet Search has obtained high-quality (R~=70,000-90,000,S/N~=300-500) echelle spectra of over 1000 nearby stars taken with theHamilton spectrograph at Lick Observatory, the HIRES spectrograph atKeck, and UCLES at the Anglo Australian Observatory. A uniform analysisof the high-resolution spectra has yielded precise stellar parameters(Teff, logg, vsini, [M/H], and individual elementalabundances for Fe, Ni, Si, Na, and Ti), enabling systematic erroranalyses and accurate theoretical stellar modeling. We have created alarge database of theoretical stellar evolution tracks using the YaleStellar Evolution Code (YREC) to match the observed parameters of theSPOCS stars. Our very dense grids of evolutionary tracks eliminate theneed for interpolation between stellar evolutionary tracks and allowprecise determinations of physical stellar parameters (mass, age,radius, size and mass of the convective zone, surface gravity, etc.).Combining our stellar models with the observed stellar atmosphericparameters and uncertainties, we compute the likelihood for each set ofstellar model parameters separated by uniform time steps along thestellar evolutionary tracks. The computed likelihoods are used for aBayesian analysis to derive posterior probability distribution functionsfor the physical stellar parameters of interest. We provide a catalog ofphysical parameters for 1074 stars that are based on a uniform set ofhigh-quality spectral observations, a uniform spectral reductionprocedure, and a uniform set of stellar evolutionary models. We explorethis catalog for various possible correlations between stellar andplanetary properties, which may help constrain the formation anddynamical histories of other planetary systems.
| New Debris Disks around Nearby Main-Sequence Stars: Impact on the Direct Detection of Planets
Using the MIPS instrument on Spitzer, we have searched for infraredexcesses around a sample of 82 stars, mostly F, G, and K main-sequencefield stars, along with a small number of nearby M stars. These starswere selected for their suitability for future observations by a varietyof planet-finding techniques. These observations provide information onthe asteroidal and cometary material orbiting these stars, data that canbe correlated with any planets that may eventually be found. We havefound significant excess 70 μm emission toward 12 stars. Combinedwith an earlier study, we find an overall 70 μm excess detection rateof 13%+/-3% for mature cool stars. Unlike the trend for planets to befound preferentially toward stars with high metallicity, the incidenceof debris disks is uncorrelated with metallicity. By newly identifyingfour of these stars as having weak 24 μm excesses (fluxes ~10% abovethe stellar photosphere), we confirm a trend found in earlier studieswherein a weak 24 μm excess is associated with a strong 70 μmexcess. Interestingly, we find no evidence for debris disks around 23stars cooler than K1, a result that is bolstered by a lack of excessaround any of the 38 K1-M6 stars in two companion surveys. Onemotivation for this study is the fact that strong zodiacal emission canmake it hard or impossible to detect planets directly with futureobservatories such as the Terrestrial Planet Finder (TPF). Theobservations reported here exclude a few stars with very high levels ofemission, >1000 times the emission of our zodiacal cloud, from directplanet searches. For the remainder of the sample, we set relatively highlimits on dust emission from asteroid belt counterparts.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| An activity catalogue of southern stars
We have acquired high-resolution echelle spectra of 225 F6-M5 type starsin the Southern hemisphere. The stars are targets or candidates to betargets for the Anglo-Australian Planet Search. CaII H& K line coreswere used to derive activity indices for all of these objects. Theindices were converted to the Mt. Wilson system of measurements andlogR'HK values determined. A number of these stars had nopreviously derived activity indices. In addition, we have also includedthe stars from Tinney et al. using our Mt. Wilson calibration. Theradial-velocity instability (also known as jitter) level was determinedfor all 21 planet-host stars in our data set. We find the jitter to beat a level considerably below the radial-velocity signatures in all butone of these systems. 19 stars from our sample were found to be active(logR'HK > -4.5) and thus have high levels of jitter.Radial-velocity analysis for planetary companions to these stars shouldproceed with caution.
| Metallicity and absolute magnitude calibrations for UBV photometry
Calibrations are presented here for metallicity ([Fe/H]) in terms of theultraviolet excess, [δ(U - B) at B - V = 0.6, hereafterδ0.6], and also for the absolute visual magnitude(MV) and its difference with respect to the Hyades(ΔMHV) in terms of δ0.6 and(B - V), making use of high-resolution spectroscopic abundances from theliterature and Hipparcos parallaxes. The relation[Fe/H]-δ0.6 has been derived for dwarf plus turn-offstars, and also for dwarf, turn-off, plus subgiant stars classifiedusing the MV-(B - V)0 plane of Fig. 11, which iscalibrated with isochrones from Bergbusch & VandenBerg (and alsoVandenBerg & Clem). The [Fe/H]-δ0.6 relations inour equations (5) and (6) agree well with those of Carney, as can beseen from Fig. 5(a). Within the uncertainties, the zero-points,+0.13(+/-0.05) of equation (5) and +0.13(+/-0.04) of equation (6), arein good agreement with the photometric ones of Cameron and of Carney,and close to the spectroscopic ones of Cayrel et al. and of Boesgaard& Friel for the Hyades open cluster. Good quantitative agreementbetween our estimated [Fe/H] abundances with those from uvby-βphotometry and spectroscopic [Fe/H]spec values demonstratesthat our equation (6) can be used in deriving quality photometric metalabundances for field stars and clusters using UBV data from variousphotometric surveys.For dwarf and turn-off stars, a new hybrid MV calibration ispresented, based on Hipparcos parallaxes withσπ/π <= 0.1 and with a dispersion of +/-0.24in MV. This hybrid MV calibration containsδ0.6 and (B - V) terms, plus higher order cross-termsof these, and is valid for the ranges of +0.37 <= (B - V)0<= +0.88,- 0.10 <= δ0.6 <= +0.29 and 3.44<= MV <= 7.23. For dwarf and turn-off stars, therelation for ΔMHV is revised and updated interms of (B - V) and δ0.6, for the ranges of -0.10<= δ0.6 <= +0.29, and +0.49 <= (B -V)0 <= +0.89, again making use of Hipparcos parallaxeswith σπ/π <= 0.1. These parallaxes formetal-poor dwarf and turn-off stars in our sample reveal that thedifference of ΔMHV(B - V) relative to Hyadesat (B - V) = +0.70 should be 1.37mag, instead of the 1.58mag given byLaird et al. In general, Hipparcos parallaxes are larger thanground-based ones, causing a divergence of ourΔMHV(B - V,δ0.6) relation(the solid line in Fig. 15b), from the one of Laird et al. (the dashedline) for the range +0.10 <= δ0.6 <= +0.29 ourabsolute magnitudes are fainter, as has been confirmed for localsubdwarfs by Reid. Our final calibrations forΔMHV(B - V, δ0.6),equations (16) and (17), are third-order polynomials inδ0.6, pass through the origin, and provide photometricdistances in reasonable agreement with those obtained directly fromHipparcos parallaxes (Fig. 18).
| Revisiting two local constraints of the Galactic chemical evolution
I review the uncertainties in two observational local constraints of theGalactic disc chemical evolution: the metallicity distribution oflong-lived dwarfs and the age-metallicity relation. Analysing mostrecent data, it is shown first that the observed metallicitydistribution at solar galactocentric radius, designed with standardmethods, is more fit to a closed-box model than to the infallmetallicity distribution. We argue that this is due to the specificcontribution of the thick-disc population, which has been overlookedboth in the derivation of the observed metallicity distribution and inthe standard chemical evolution models. Although this agreementdisqualifies the metallicity distribution as the best supportive(indirect) evidence for infall, we argue that the evolution must be morecomplex than described by either the closed-box or the standard infallmodels.It is then shown that recent determinations of the age-metallicitydistribution (AMD) from large Strömgren photometric surveys aredominated by noise resulting from systematic biases in metallicities andeffective temperatures. These biases are evaluated and a new AMD isobtained, where particularities of the previous determinations arephased out. The new age-metallicity relation shows a mean increaselimited to about a factor of 2 in Z over the disc age. It is shown thatbelow 3 Gyr, the dispersion in metallicity is about 0.1 dex, which,given the observational uncertainties in the derived metallicities, iscompatible with the small cosmic dispersion measured on the interstellarmedium and meteoritic pre-solar dust grains. A population that isprogressively older and more metal rich arises at a metallicity greaterthan that of the Hyades, to reach [Fe/H] ~ +0.5 dex at ages greater than5 Gyr. We suggest that this is best explained by radial migration. Asymmetrical widening of the metallicity interval towards lower values isseen at about the same age, which is attributed to a similar cause.Finally, the new derived ages are sufficiently consistent that anage-metallicity relation within the thick disc is confirmed. These newfeatures altogether draw a picture of the chemical evolution in thesolar neighbourhood where dynamical effects and complexity in the AMDdominate, rather than a generalized high dispersion at all ages.
| Indium abundance trends among sun-like stars
Results are presented from the first abundance analysis of indium (In)among sun-like stars. The abundance analysis is based on the weak InIline at 4511 Å. Spectrum synthesis of 42 stars cooler than the sunreveals a trend between [In/Fe] and [Fe/H] with a slope of -0.76 +/-0.06, when corrected for a trend with Teff. This is the samesense as the correlation found among sun-like stars for the r-processelement, Eu, but In exhibits a much steeper slope. The sample includesfive stars hosting giant planets, but they exhibit the same trend as theother stars in the sample. Additional research on all astrophysicalprocesses affecting the In abundance in stars is encouraged.
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample
We are obtaining spectra, spectral types, and basic physical parametersfor the nearly 3600 dwarf and giant stars earlier than M0 in theHipparcos catalog within 40 pc of the Sun. Here we report on resultsfor 1676 stars in the southern hemisphere observed at Cerro TololoInter-American Observatory and Steward Observatory. These resultsinclude new, precise, homogeneous spectral types, basic physicalparameters (including the effective temperature, surface gravity, andmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. We include notes on astrophysically interesting stars inthis sample, the metallicity distribution of the solar neighborhood, anda table of solar analogs. We also demonstrate that the bimodal nature ofthe distribution of the chromospheric activity parameterlogR'HK depends strongly on the metallicity, andwe explore the nature of the ``low-metallicity'' chromosphericallyactive K-type dwarfs.
| 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.
| How Dry is the Brown Dwarf Desert? Quantifying the Relative Number of Planets, Brown Dwarfs, and Stellar Companions around Nearby Sun-like Stars
Sun-like stars have stellar, brown dwarf, and planetary companions. Tohelp constrain their formation and migration scenarios, we analyze theclose companions (orbital period <5 yr) of nearby Sun-like stars. Byusing the same sample to extract the relative numbers of stellar, browndwarf, and planetary companions, we verify the existence of a very drybrown dwarf desert and describe it quantitatively. With decreasing mass,the companion mass function drops by almost 2 orders of magnitude from 1Msolar stellar companions to the brown dwarf desert and thenrises by more than an order of magnitude from brown dwarfs toJupiter-mass planets. The slopes of the planetary and stellar companionmass functions are of opposite sign and are incompatible at the 3σ level, thus yielding a brown dwarf desert. The minimum number ofcompanions per unit interval in log mass (the driest part of the desert)is at M=31+25-18MJ. Approximately 16%of Sun-like stars have close (P<5 yr) companions more massive thanJupiter: 11%+/-3% are stellar, <1% are brown dwarf, and 5%+/-2% aregiant planets. The steep decline in the number of companions in thebrown dwarf regime, compared to the initial mass function of individualstars and free-floating brown dwarfs, suggests either a differentspectrum of gravitational fragmentation in the formation environment orpost-formation migratory processes disinclined to leave brown dwarfs inclose orbits.
| 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.
| 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.
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Observation and Astrometry data
| Constellation: | Capricornus |
| Right ascension: | 20h15m17.39s |
| Declination: | -27°01'58.7" |
| Apparent magnitude: | 5.73 |
| Proper motion RA: | 1241.9 |
| Proper motion Dec: | -180.8 |
| B-T magnitude: | 6.86 |
| V-T magnitude: | 5.824 |
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INHABITED SKY
