Contents
Images
Upload your image
DSS Images Other Images
Related articles
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.
| 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.
| Single-Visit Photometric and Obscurational Completeness
We report a method that uses ``completeness'' to estimate the number ofextrasolar planets discovered by an observing program with adirect-imaging instrument. We develop a completeness function forEarth-like planets on ``habitable'' orbits for an instrument with acentral field obscuration, uniform sensitivity in an annular detectionzone, and limiting sensitivity that is expressed as a ``deltamagnitude'' with respect to the star, determined by systematic effects(given adequate exposure time). We demonstrate our method of estimationby applying it to our understanding of the coronagraphic version of theTerrestrial Planet Finder (TPF-C) mission as of 2004 October. Weestablish an initial relationship between the size, quality, andstability of the instrument's optics and its ability to meet missionscience requirements. We provide options for increasing the fidelity andversatility of the models on which our method is based, and we discusshow the method could be extended to model the TPF-C mission as a wholeto verify that its design can meet the science requirements.
| 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.
| 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.
| 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.
| C, S, Zn and Cu abundances in planet-harbouring stars
We present a detailed and uniform study of C, S, Zn and Cu abundances ina large set of planet host stars, as well as in a homogeneous comparisonsample of solar-type dwarfs with no known planetary-mass companions.Carbon abundances were derived by EW measurement of two C I opticallines, while spectral syntheses were performed for S, Zn and Cu. Weinvestigated possible differences in the behaviours of the volatiles C,S and Zn and in the refractory Cu in targets with and without knownplanets in order to check possible anomalies due to the presence ofplanets. We found that the abundance distributions in stars withexoplanets are the high [Fe/H] extensions of the trends traced by thecomparison sample. All volatile elements we studied show [X/Fe] trendsdecreasing with [Fe/H] in the metallicity range -0.8< [Fe/H] <0.5, with significantly negative slopes of -0.39±0.04 and-0.35±0.04 for C and S, respectively. A comparison of ourabundances with those available in the literature shows good agreementin most cases.Based on observations collected at the La Silla Observatory, ESO(Chile), with the CORALIE spectrograph at the 1.2-m Euler Swisstelescope and with the FEROS spectrograph at the 1.52-m and 2.2-m ESOtelescopes, at the Paranal Observatory, ESO (Chile), using the UVESspectrograph at the VLT/UT2 Kueyen telescope, and with the UES and SARGspectrographs at the 4-m William Hershel Telescope (WHT) and at the3.5-m TNG telescope, respectively, both at La Palma (Canary Islands).Tables 4-16 are only available in electronic form athttp://www.edpsciences.org
| Chemical enrichment and star formation in the Milky Way disk. III. Chemodynamical constraints
In this paper, we investigate some chemokinematical properties of theMilky Way disk, by using a sample composed by 424 late-type dwarfs. Weshow that the velocity dispersion of a stellar group correlates with theage of this group, according to a law proportional to t0.26,where t is the age of the stellar group. The temporal evolution of thevertex deviation is considered in detail. It is shown that the vertexdeviation does not seem to depend strongly on the age of the stellargroup. Previous studies in the literature seem to not have found it dueto the use of statistical ages for stellar groups, rather thanindividual ages. The possibility to use the orbital parameters of a starto derive information about its birthplace is investigated, and we showthat the mean galactocentric radius is likely to be the most reliablestellar birthplace indicator. However, this information cannot bepresently used to derive radial evolutionary constraints, due to anintrinsic bias present in all samples constructed from nearby stars. Anextensive discussion of the secular and stochastic heating mechanismscommonly invoked to explain the age-velocity dispersion relation ispresented. We suggest that the age-velocity dispersion relation couldreflect the gradual decrease in the turbulent velocity dispersion fromwhich disk stars form, a suggestion originally made by Tinsley &Larson (\cite{tinsley}, ApJ, 221, 554) and supported by several morerecent disk evolution calculations. A test to distinguish between thetwo types of models using high-redshift galaxies is proposed.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/423/517
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| Spectroscopic [Fe/H] for 98 extra-solar planet-host stars. Exploring the probability of planet formation
We present stellar parameters and metallicities, obtained from adetailed spectroscopic analysis, for a large sample of 98 stars known tobe orbited by planetary mass companions (almost all known targets), aswell as for a volume-limited sample of 41 stars not known to host anyplanet. For most of the stars the stellar parameters are revisedversions of the ones presented in our previous work. However, we alsopresent parameters for 18 stars with planets not previously published,and a compilation of stellar parameters for the remaining 4 planet-hostsfor which we could not obtain a spectrum. A comparison of our stellarparameters with values of Teff, log g, and [Fe/H] availablein the literature shows a remarkable agreement. In particular, ourspectroscopic log g values are now very close to trigonometric log gestimates based on Hipparcos parallaxes. The derived [Fe/H] values arethen used to confirm the previously known result that planets are moreprevalent around metal-rich stars. Furthermore, we confirm that thefrequency of planets is a strongly rising function of the stellarmetallicity, at least for stars with [Fe/H] > 0. While only about 3%of the solar metallicity stars in the CORALIE planet search sample werefound to be orbited by a planet, this number increases to more than 25%for stars with [Fe/H] above +0.3. Curiously, our results also suggestthat these percentages might remain relatively constant for values of[Fe/H] lower than about solar, increasing then linearly with the massfraction of heavy elements. These results are discussed in the contextof the theories of planetary formation.Based on observations collected at the La Silla Observatory, ESO(Chile), with the CORALIE spectrograph at the 1.2-m Euler Swisstelescope and the FEROS spectrograph at the 1.52-m and 2.2-m ESOtelescopes, with the VLT/UT2 Kueyen telescope (Paranal Observatory, ESO,Chile) using the UVES spectrograph (Observing run 67.C-0206, in servicemode), with the TNG and William Herschel Telescopes, both operated atthe island of La Palma, and with the ELODIE spectrograph at the 1.93-mtelescope at the Observatoire de Haute Provence.
| Lithium in stars with exoplanets
We present a comparison of the lithium abundances of stars with andwithout planetary-mass companions. New lithium abundances are reportedin 79 planet hosts and 38 stars from a comparison sample. When the Liabundances of planet host stars are compared with the 157 stars in thesample of field stars of Chen et al. (\cite{Chen2001}) we find that theLi abundance distribution is significantly different, and that there isa possible excess of Li depletion in planet host stars with effectivetemperatures in the range 5600-5850 K, whereas we find no significantdifferences in the temperature range 5850-6350 K. We have searched forstatistically significant correlations between the Li abundance ofparent stars and various parameters of the planetary companions. We donot find any strong correlation, although there are may be a hint of apossible gap in the Li distribution of massive planet host stars.Based on observations collected at the La Silla Observatory, ESO(Chile), with the CORALIE spectrograph at the 1.2 m Euler Swisstelescope, and with the FEROS spectrograph at the 1.52 m ESO telescope,and using the UES spectrograph at the 4.2 m William Herschel Telescope(WHT) and SARG spectrograph at the 3.5 m Telescopio Nazional Galileo onLa Palma (Canary Islands).
| New Metallicity Calibration Down to [Fe/H] = -2.75 dex
We have taken 88 dwarfs, covering the colour-index interval 0.37 <=(B-V)0 <= 1.07mag, with metallicities -2.70 <= [Fe/H]<= +0.26dex, from three different sources for new metallicitycalibration. The catalogue of Cayrel de Stroble et al. (2001), whichincludes 65% of the stars in our sample, supplies detailed informationon abundances for stars with determination based on high-resolutionspectroscopy. In constructing the new calibration we have used as`corner stones' 77 stars which supply at least one of the followingconditions: (i) the parallax is larger than 10mas (distance relative tothe Sun less than 100pc) and the galactic latitude is absolutely higherthan 30° (ii) the parallax is rather large, if the galactic latitudeis absolutely low and vice versa. Contrary to previous investigations, athird-degree polynomial is fitted for the new calibration: [Fe/H]=0.10 -2.76δ - 24.04δ2 + 30.00δ3. Thecoefficients were evaluated by the least-squares method, without regardto the metallicity of Hyades. However, the constant term is in the rangeof metallicity determined for this cluster, i.e.0.08<=[Fe/H]<=0.11dex. The mean deviation and the mean error inour work are equal to those of Carney (1979), for [Fe/H] >= -1.75dexwhere Carney's calibration is valid
| Some anomalies in the occurrence of debris discs around main-sequence A and G stars
Debris discs consist of large dust grains that are generated bycollisions of comets or asteroids around main-sequence stars, and thequantity and distribution of debris may be used to detect the presenceof perturbing planets akin to Neptune. We use stellar and disc surveysto compare the material seen around A- and G-type main-sequence stars.Debris is detected much more commonly towards A stars, even when acomparison is made only with G stars of comparable age. Detection ratesare consistent with disc durations of ~0.5 Gyr, which may occur at anytime during the main sequence. The higher detection rate for A stars canresult from this duration being a larger fraction of the main-sequencelifetime, possibly boosted by a globally slightly larger disc mass thanfor the G-type counterparts. The disc mass range at any given age is afactor of at least ~100 and any systematic decline with time is slow,with a power law estimated to not be steeper than t-1/2.Comparison with models shows that dust can be expected as late as a fewGyr when perturbing planetesimals form slowly at large orbital radii.Currently, the Solar system has little dust because the radius of theKuiper Belt is small and hence the time-scale to produce planetesimalswas less than 1 Gyr. However, the apparently constant duration of ~0.5Gyr when dust is visible is not predicted by the models.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Chemical abundances of planet-host stars. Results for alpha and Fe-group elements
In this paper, we present a study of the abundances of Si, Ca, Sc, Ti,V, Cr, Mn, Co, and Ni in a large set of stars known to harbor giantplanets, as well as in a comparison sample of stars not known to haveany planetary-mass companions. We have checked for possible chemicaldifferences between planet hosts and field stars without known planets.Our results show that overall, and for a given value of [Fe/H], theabundance trends for the planet hosts are nearly indistinguishable fromthose of the field stars. In general, the trends show nodiscontinuities, and the abundance distributions of stars with giantplanets are high [Fe/H] extensions to the curves traced by the fielddwarfs without planets. The only elements that might present slightdifferences between the two groups of stars are V, Mn, and to a lesserextent Ti and Co. We also use the available data to describe galacticchemical evolution trends for the elements studied. When comparing theresults with former studies, a few differences emerge for the high[Fe/H] tail of the distribution, a region that is sampled withunprecedented detail in our analysis.Based on observations collected at the La Silla Observatory, ESO(Chile), with the CORALIE spectrograph at the 1.2-m Euler Swisstelescope and the FEROS spectrograph at the 1.52-m ESO telescope, withthe VLT/UT2 Kueyen telescope (Paranal Observatory, ESO, Chile) using theUVES spectrograph (Observing run 67.C-0206, in service mode), with theTNG and William Herschel Telescopes, both operated at the island of LaPalma, and with the ELODIE spectrograph at the 1.93-m telescope at theObservatoire de Haute Provence.
| The Wilson-Bappu effect: A tool to determine stellar distances
Wilson & Bappu (\cite{orig}) have shown the existence of aremarkable correlation between the width of the emission in the core ofthe K line of Ca II and the absolute visual magnitude of late-typestars.Here we present a new calibration of the Wilson-Bappu effect based on asample of 119 nearby stars. We use, for the first time, widthmeasurements based on high resolution and high signal to noise ratio CCDspectra and absolute visual magnitudes from the Hipparcos database.Our primary goal is to investigate the possibility of using theWilson-Bappu effect to determine accurate distances to single stars andgroups.The result of our calibration fitting of the Wilson-Bappu relationshipis MV=33.2-18.0 log W0, and the determinationseems free of systematic effects. The root mean square error of thefitting is 0.6 mag. This error is mostly accounted for by measurementerrors and intrinsic variability of W0, but in addition apossible dependence on the metallicity is found, which becomes clearlynoticeable for metallicities below [Fe/H] ~ -0.4. This detection ispossible because in our sample [Fe/H] ranges from -1.5 to 0.4.The Wilson-Bappu effect can be used confidently for all metallicitiesnot lower than ~ -0.4, including the LMC. While it does not provideaccurate distances to single stars, it is a useful tool to determineaccurate distances to clusters and aggregates, where a sufficient numberof stars can be observed.We apply the Wilson-Bappu effect to published data of the open cluster M67; the retrieved distance modulus is of 9.65 mag, in very goodagreement with the best distance estimations for this cluster, based onmain sequence fitting.Observations collected at ESO, La Silla.
| Statistical cataloging of archival data for luminosity class IV-V stars. II. The epoch 2001 [Fe/H] catalog
This paper describes the derivation of an updated statistical catalog ofmetallicities. The stars for which those metallicities apply are ofspectral types F, G, and K, and are on or near the main sequence. Theinput data for the catalog are values of [Fe/H] published before 2002February and derived from lines of weak and moderate strength. Theanalyses used to derive the data have been based on one-dimensional LTEmodel atmospheres. Initial adjustments which are applied to the datainclude corrections to a uniform temperature scale which is given in acompanion paper (see Taylor \cite{t02}). After correction, the data aresubjected to a statistical analysis. For each of 941 stars considered,the results of that analysis include a mean value of [Fe/H], an rmserror, an associated number of degrees of freedom, and one or moreidentification numbers for source papers. The catalog of these resultssupersedes an earlier version given by Taylor (\cite{t94b}).Catalog is only available in electronic form at the CDS via anonymousftp cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/731
| Statistical cataloging of archival data for luminosity class IV-V stars. I. The epoch 2001 temperature catalog
This paper is one of a pair in which temperatures and metallicitycatalogs for class IV-V stars are considered. The temperature catalogdescribed here is derived from a calibration based on stellar angulardiameters. If published calibrations of this kind are compared by usingcolor-index transformations, temperature-dependent differences among thecalibrations are commonly found. However, such differences are minimizedif attention is restricted to calibrations based on Johnson V-K. Acalibration of this sort from Di Benedetto (\cite{dib98}) is thereforetested and adopted. That calibration is then applied to spectroscopicand photometric data, with the latter predominating. Cousins R-Iphotometry receives special attention because of its high precision andlow metallicity sensitivity. Testing of temperatures derived from thecalibration suggests that their accuracy and precision are satisfactory,though further testing will be warranted as new results appear. Thesetemperatures appear in the catalog as values of theta equiv5040/T(effective). Most of these entries are accompanied by measured orderived values of Cousins R-I. Entries are given for 951 stars.Catalog is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/721
| Rotation and differential rotation in field F- and G-type stars
We present a detailed study of rotation and differential rotationanalyzing high resolution high S/N spectra of 142 F-, G- and earlyK-type field stars. Using Least Squares Deconvolution we obtainbroadening profiles for our sample stars and use the Fourier transformmethod to determine projected rotational velocities v sin i.Distributions of rotational velocities and periods are studied in theHR-diagram. For a subsample of 32 stars of spectral type F0-G0 we derivethe amount of differential rotation in terms of alpha = (Omega_Equator- Omega_Pole )/Omega_Equator . We find evidence for differentialrotation in ten of the 32 stars. Differential rotation seems to be morecommon in slower rotators, but deviations from rigid rotation are alsofound in some fast rotators. We search for correlations betweendifferential rotation and parameters relevant for stellar activity andshow indications against strong differential rotation in very activestars. We derive values of Delta P and Delta Omega , which support aperiod dependence of differential rotation. Derived lap times 2pi /DeltaOmega are of the order of 20 d and contradict the assumption thatconstant lap times of the order of the solar one ( ~ 130 d) are therule in stars that are thought to harbour magnetic dynamos.Based on observations collected at the European Southern Observatory, LaSilla.Tables 3 and A1 are only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/647
| Extrasolar planets around HD 196050, HD 216437 and HD 160691
We report precise Doppler measurements of the stars HD 216437, HD 196050and HD 160691 obtained with the Anglo-Australian Telescope using theUCLES spectrometer together with an iodine cell as part of theAnglo-Australian Planet Search. Our measurements reveal periodicKeplerian velocity variations that we interpret as evidence for planetsin orbit around these solar type stars. HD 216437 has a period of 1294+/- 250 d, a semi-amplitude of 38 +/- 3 m s-1 and aneccentricity of 0.33 +/- 0.09. The minimum (M sin i) mass of thecompanion is 2.1 +/- 0.3 MJUP and the semi-major axis is 2.4+/- 0.5 au. HD 196050 has a period of 1300 +/- 230 d, a semi-amplitudeof 49 +/- 8 m s-1 and an eccentricity of 0.19 +/- 0.09. Theminimum mass of the companion is 2.8 +/- 0.5 MJUP and thesemi-major axis is 2.4 +/- 0.5 au. We also report further observationsof the metal-rich planet bearing star HD 160691. Our new solutionconfirms the previously reported planet and shows a trend indicating asecond, longer-period companion. These discoveries add to the growingnumbers of mildly eccentric, long-period extrasolar planets aroundmetal-rich Sun-like stars.
| Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalog
We present refined coordinates and proper-motion data for the highproper-motion (HPM) stars in the Luyten Half-Second (LHS) catalog. Thepositional uncertainty in the original Luyten catalog is typicallygreater than 10" and is often greater than 30". We have used the digitalscans of the POSS I and POSS II plates to derive more accurate positionsand proper motions of the objects. Out of the 4470 candidates in the LHScatalog, 4323 objects were manually reidentified in the POSS I and POSSII scans. A small fraction of the stars were not found because of thelack of finder charts and digitized POSS II scans. The uncertainties inthe revised positions are typically ~2" but can be as high as ~8" in afew cases, which is a large improvement over the original data.Cross-correlation with the Tycho-2 and Hipparcos catalogs yielded 819candidates (with mR<~12). For these brighter sources, theposition and proper-motion data were replaced with the more accurateTycho-2/Hipparcos data. In total, we have revised proper-motionmeasurements and coordinates for 4040 stars and revised coordinates for4330 stars. The electronic version of the paper5 contains the updated information on all 4470stars in the LHS catalog.
| A revision of the solar neighbourhood metallicity distribution
We present a revised metallicity distribution of dwarfs in the solarneighbourhood. This distribution is centred on solar metallicity. Weshow that previous metallicity distributions, selected on the basis ofspectral type, are biased against stars with solar metallicity orhigher. A selection of G-dwarf stars is inherently biased againstmetal-rich stars and is not representative of the solar neighbourhoodmetallicity distribution. Using a sample selected on colour, we obtain adistribution where approximately half the stars in the solarneighbourhood have metallicities higher than [Fe/H]=0. The percentage ofmid-metal-poor stars ([Fe/H]<-0.5) is approximately 4 per cent, inagreement with present estimates of the thick disc. In order to have ametallicity distribution comparable to chemical evolution modelpredictions, we convert the star fraction to mass fraction, and showthat another bias against metal-rich stars affects dwarf metallicitydistributions, due to the colour (or spectral type) limits of thesamples. Reconsidering the corrections resulting from the increasingthickness of the stellar disc with age, we show that the simpleclosed-box model with no instantaneous recycling approximation gives areasonable fit to the observed distribution. Comparisons with theage-metallicity relation and abundance ratios suggest that the simpleclosed-box model may be a viable model of the chemical evolution of theGalaxy at solar radius.
| The metal-rich nature of stars with planets
With the goal of confirming the metallicity ``excess'' present in starswith planetary-mass companions, we present in this paper ahigh-precision spectroscopic study of a sample of dwarfs included in theCORALIE extrasolar planet survey. The targets were chosen according tothe basic criteria that 1) they formed part of a limited volume and 2)they did not present the signature of a planetary host companion. A fewstars with planets were also observed and analysed; namely, HD6434, HD 13445 (Gl 86), HD16141, HD 17051 (iota Hor), HD19994, HD 22049 (epsilon Eri), HD28185, HD 38529, HD52265, HD 190228, HD210277 and HD 217107. For some of theseobjects there had been no previous spectroscopic studies. Thespectroscopic analysis was done using the same technique as in previouswork on the metallicity of stars with planets, thereby permitting adirect comparison of the results. The work described in this paper thusrepresents the first uniform and unbiased comparison between stars withand without planetary-mass companions in a volume-limited sample. Theresults show that 1) stars with planets are significantly metal-rich,and 2) that the source of the metallicity is most probably``primordial''. The results presented here may impose seriousconstraints on planetary system formation and evolution models. Based onobservations collected at the La Silla Observatory, ESO (Chile), withthe spectrograph at the Euler Swiss telescope, with the spectrograph atthe 1.52-m ESO telescope (Observing run 66.C-0116 B), and using the UESspectrograph at the 4-m William Hershel Telescope (WHT), at La Palma(Canary Islands).
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Radial Velocities, Binarity, and Kinematic Membership in the Open Cluster NGC 2516
We present echelle spectroscopic observations for 36 bright (V<9.6)stars in the open cluster NGC 2516, including several blue stragglercandidates and four red giants. Radial velocities are derived bycross-correlations using high signal-to-noise ratio standard spectra astemplates. From 22 cluster members a mean cluster velocity of+22.0+/-0.2 km s-1 was derived. Membership probabilities ofthe observed stars are computed on the basis of their distance to thecluster center and kinematic criteria. We report the discovery of threedouble-lined spectroscopic binaries and several probable binaries amongmain-sequence stars. A binary frequency of more than 26% is found amongthe high-mass main-sequence stars. The blue straggler HD 66341 is aslowly rotating cluster member with constant velocity, while HD 66194 isa fast-rotating Be star with probable variations in radial velocity.Other blue straggler candidates, such as HD 65663, 65950, 66066, and65987, must be considered turnoff stars. The observations presented herewere obtained at the Complejo Astronómico El Leoncito (CASLEO),which is operated under agreement between the Consejo Nacional deInvestigaciones Científicas y Técnicas de laRepública Argentina (CONICET) and the national universities of LaPlata, Córdoba, and San Juan.
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A systematic analysis of X-ray variability of dM stars
We have systematically analyzed X-ray variability of dM stars. Our database is the sample of all dM stars listed in the CNS3 (Gliese &Jahreiss 1991) catalog which have been observed with the ROSAT PSPC. Ourdata sample includes 86 pointed observations of 55 distinct stars ormultiple systems. A large fraction of stars shows significantvariations, regardless of their quiescent flux. Variability is detectedon all observable time scales. The amplitudes of these variations areindependent of both stellar X-ray and visual luminosity. Compared tosolar X-ray variability properties our results suggest that theamplitude distribution of X-ray variability in dM stars is consistentwith the analogous distribution for solar flares. We discuss the effectof variability on the spread observed in the X-ray luminosity functionof M stars. The comparison of our data with those obtained with EinsteinIPC shows that variations on time scales shorter than a few month aremore common than long term variations comparable to, e.g., the 11 yearssolar cycle.
| The galactic lithium evolution revisited
The evolution of the 7Li abundance in the Galaxy has beencomputed by means of the two-infall model of Galactic chemicalevolution. We took into account several stellar 7Li sources:novae, massive AGB stars, C-stars and Type II SNe. In particular, weadopted new theoretical yields for novae. We also took into account the7Li production from GCRs. In particular, the absolute yieldsof 7Li, as suggested by a recent reevaluation of thecontribution of GCR spallation to the 7Li abundance, havebeen adopted. We compared our theoretical predictions for the evolutionof 7Li abundance in the solar neighborhood with a newcompilation of data, where we identified the population membership ofthe stars on a kinematical basis. A critical analysis of extantobservations revealed a possible extension of the Li plateau towardshigher metallicities (up to [Fe/H] ~ -0.5 or even -0.3) with a steeprise afterwards. We conclude that 1) the 7Li contributionfrom novae is required in order to reproduce the shape of the growth ofA(Li) versus [Fe/H], 2) the contribution from Type II SNe should belowered by at least a factor of two, and 3) the 7Liproduction from GCRs is probably more important than previouslyestimated, in particular at high metallicities: by taking into accountGCR nucleosynthesis we noticeably improved the predictions on the7Li abundance in the presolar nebula and at the present timeas inferred from measures in meteorites and T Tauri stars, respectively.We also predicted a lower limit for the present time 7Liabundance expected in the bulge, a prediction which might be tested byfuture observations. Tables~3 and 4 are only available in electronicform at the CDS via anonymous ftp to: cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/Abstract.html
| Metallicity effects on the chromospheric activity-age relation for late-type dwarfs
We show that there is a relationship between the age excess, defined asthe difference between the stellar isochrone and chromospheric ages, andthe metallicity as measured by the index [Fe/H] for late-type dwarfs.The chromospheric age tends to be lower than the isochrone age formetal-poor stars, and the opposite occurs for metal-rich objects. Wesuggest that this could be an effect of neglecting the metallicitydependence of the calibrated chromospheric emission-age relation. Wepropose a correction to account for this dependence. We also investigatethe metallicity distributions of these stars, and show that there aredistinct trends according to the chromospheric activity level. Inactivestars have a metallicity distribution which resembles the metallicitydistribution of solar neighbourhood stars, while active stars appear tobe concentrated in an activity strip on the logR'_HKx[Fe/H] diagram. Weprovide some explanations for these trends, and show that thechromospheric emission-age relation probably has different slopes on thetwo sides of the Vaughan-Preston gap.
| A Multiplicity Survey of Chromospherically Active and Inactive Stars
Surveys of three samples of solar-type stars, segregated bychromospheric emission level, were made to determine their multiplicityfractions and to investigate the evolution of multiplicity with age. Intotal, 245 stars were searched for companions with DeltaV <= 3.0 andseparations of 0.035" to 1.08" using optical speckle interferometry. Byincorporating the visual micrometer survey for duplicity of theLamontHussey Observatory, the angular coverage was extended to 5.0" withno change in the DeltaV limit. This magnitude difference allows massratios of 0.63 and larger to be detected throughout a search region of2-127 AU for the stars observed. The 84 primaries observed in thechromospherically active sample are presumably part of a youngpopulation and are found to have a multiplicity fraction of 17.9% +/-4.6%. The sample of 118 inactive, presumably older, primaries wereselected and observed using identical methods and are found to have amultiplicity fraction of only 8.5% +/- 2.7%. Given the known linkbetween chromospheric activity and age, these results tentatively implya decreasing stellar multiplicity fraction from 1 to 4 Gyr, theapproximate ages of the two samples. Finally, only two of the 14 veryactive primaries observed were found to have a companion meeting thesurvey detection parameters. In this case, many of the systems areeither very young, or close, RS CVn type multiples that are unresolvableusing the techniques employed here.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Carina |
| Right ascension: | 07h57m46.90s |
| Declination: | -60°18'12.0" |
| Apparent magnitude: | 5.6 |
| Distance: | 16.192 parsecs |
| Proper motion RA: | 518 |
| Proper motion Dec: | 119.6 |
| B-T magnitude: | 6.252 |
| V-T magnitude: | 5.643 |
Catalogs and designations:
|
INHABITED SKY
