Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
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.
| Abundance ratios of volatile vs. refractory elements in planet-harbouring stars: hints of pollution?
We present the [ X/H] trends as a function of the elemental condensationtemperature TC in 88 planet host stars and in avolume-limited comparison sample of 33 dwarfs without detected planetarycompanions. We gathered homogeneous abundance results for many volatileand refractory elements spanning a wide range of T_C, from a few dozento several hundred kelvin. We investigate possible anomalous trends ofplanet hosts with respect to comparison sample stars to detect evidenceof possible pollution events. No significant differences are found inthe behaviour of stars with and without planets. This is consistent witha "primordial" origin of the metal excess in planet host stars. However,a subgroup of 5 planet host and 1 comparison sample stars stands out ashaving particularly high [ X/H] vs. TC slopes.
| 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.
| 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.
| New Hipparcos-based Parallaxes for 424 Faint Stars
We present a catalog of 424 common proper-motion companions to Hipparcosstars with good (>3 σ) parallaxes, thereby effectively providingnew parallaxes for these companions. Compared with typical stars in theHipparcos catalog, these stars are substantially dimmer. The catalogincludes 20 white dwarfs and an additional 29 stars withMV>14, the great majority of the latter being M dwarfs.
| Multiple Companions to HD 154857 and HD 160691
Precise Doppler measurements from the Anglo-Australian Telescope (AAT)UCLES spectrometer reveal two companions to both HD 154857 and HD160691. The inner companion to HD 154857 has a period of 398 days, aneccentricity of 0.51, and a minimum mass of 1.8MJ. An outercompanion has a period much longer than 2 yr and is currently detectedonly as a linear trend of 14 m s-1 yr-1. The innercompanion to HD 160691, previously announced from AAT data, has a periodof 645 days, an eccentricity of 0.20, and a minimum mass of1.7MJ. For the outer planet, whose orbit is less wellconstrained, a two-Keplerian fit yields a period of 8.2 yr, aneccentricity of 0.57, and a minimum mass of 3.1MJ. With theseorbital parameters, its maximum separation from the star of 0.4" makesit a viable target for direct imaging.Based on observations obtained at the Anglo-Australian Telescope, SidingSpring, Australia.
| Orbital Parameters for the Black Hole Binary XTE J1650-500
We present R-band photometry of the X-ray transient and candidate blackhole binary XTE J1650-500 obtained between 2003 May and August with the6.5 m Clay telescope. A timing analysis of these data reveals aphotometric period of 0.3205+/-0.0007 days (i.e., 7.63 hr) with apossible alias at 0.3785 days (9.12 hr). Our photometry completely rulesout the previously published spectroscopic period of 0.212 days (5.09hr). Consequently, we reanalyzed the 15 archival ESO VLT spectra(obtained 2002 June by Sanchez-Fernandez et al.) that were the basis ofthe previously published spectroscopic period. We used a ``rest-framesearch'' technique that is well suited for cases in which thesignal-to-noise ratio of individual spectra is low. For each of roughly1.1 million binary ephemerides, we summed all of the spectra in a trialrest frame of the secondary star, and each rest-frame spectrum wascross-correlated against a template spectrum. We then searched for theset of orbital parameters that produced the strongest cross-correlationvalue. The results confirmed the photometric period of 0.3205 days andruled out the alias period near 0.38 days. The best value for thevelocity semiamplitude of the companion star is K2=435+/-30km s-1, and the corresponding optical mass function isf(M)=2.73+/-0.56 Msolar. The spectral type of the companionstar is not well constrained because we only have six template spectraavailable to us. The K4 V template provides the best match; next-bestmatches are provided by the G5 V and K2 III templates. We also find thatthe accretion disk dominates the light in the R band where the diskfraction is 80% or higher, although this value should be treated withcaution owing to the poor signal-to-noise ratio and the limited numberof templates. The amplitude of the phased R-band light curve is 0.2 mag,which gives a lower limit to the inclination of50deg+/-3deg in the limiting case of nocontribution to the R-band light curve from the accretion disk. If themass ratio of XTE J1650-500 is similar to the mass ratios of other blackhole binaries, such as A0620-00 or GRS 1124-683 (e.g., Q>~10), thenour lower limit to the inclination gives an upper limit to the mass ofthe black hole in XTE J1650-500 of M1<~7.3Msolar. However, the mass can be considerably lower if theR-band flux is dominated by the accretion disk. For example, if theaccretion disk does contribute 80% of the flux, as our preliminaryresults suggest, then the black hole mass would be only about 4Msolar.Based on observations made with the Magellan 6.5 m Clay telescope at LasCampanas Observatory of the Carnegie Institution and with EuropeanSouthern Observatory (ESO) telescopes at the Paranal Observatory underprogram ID 69.D-0644(A).
| 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).
| 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.
| 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
| 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.
| 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
| The infrared triplet lines of ionized calcium as a diagnostic tool for F, G, K-type stellar atmospheres
LTE calculations of the profiles of the infrared triplet lines ofionized calcium in the spectrum of F, G and K stars are described indetail with explicit quantitative consideration of their perturbation byhydrogen Paschen lines. The results of such calculations obtained withfive different solar model atmospheres are discussed. The sensitivity ofthe profiles to changes in basic stellar atmospheric parameters isillustrated. The flux in the center of the lambda 8542 Ä line isrelated empirically to the Mount-Wilson chromospheric activity indicatorR'HK. The predictive power of observations of the infraredtriplet lines is then summed up.
| 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.
| Kinematics and Metallicity of Stars in the Solar Region
Several samples of nearby stars with the most accurate astrometric andphotometric parameters are searched for clues to their evolutionaryhistory. The main samples are (1) the main-sequence stars with b - ybetween 0.29 and 0.59 mag (F3 to K1) in the Yale parallax catalog, (2) agroup of high-velocity subgiants studied spectroscopically by Ryan &Lambert, and (3) high-velocity main-sequence stars in the extensiveinvestigation by Norris, Bessel, & Pickles. The major conclusionsare as follows: (1) The oldest stars (halo), t >= 10-12 Gyr, haveV-velocities (in the direction of Galactic rotation and referred to theSun) in the range from about -50 to -800 km s^-1 and have aheavy-element abundance [Fe/H] of less than about -0.8 dex. The agerange of these objects depends on our knowledge of globular clusterages, but if age is correlated with V-velocity, the youngest may be M22and M28 (V ~ -50 km s^-1) and the oldest NGC 3201 (V ~ -500 km s^-1) andassorted field stars. (2) The old disk population covers the large agerange from about 2 Gyr (Hyades, NGC 752) to 10 or 12 Gyr (Arcturusgroup, 47 Tuc), but the lag (V) velocity is restricted to less thanabout 120 km s^-1 and [Fe/H] >= -0.8 or -0.9 dex. The [Fe/H] ~ -0.8dex division between halo and old disk, near t ~ 10-12 Gyr, is marked bya change in the character of the CN index (C_m) and of the blanketingparameter K of the DDO photometry. (3) The young disk population, t <2 Gyr, is confined exclusively to a well-defined area of the (U, V)velocity plane. The age separating young and old disk stars is also thatseparating giant evolution of the Hyades (near main-sequence luminosity)and M67 (degenerate helium cores and a large luminosity rise) kinds. Thetwo disk populations are also separated by such indexes as the g-indexof Geveva photometry. There appears to be no obvious need to invokeexogeneous influences to understand the motion and heavy-elementabundance distributions of the best-observed stars near the Sun.Individual stars of special interest include the parallax star HD 55575,which may be an equal-component binary, and the high-velocity star HD220127, with a well-determined space velocity near 1000 km s^-1.
| Determination of the temperatures of selected ISO flux calibration stars using the Infrared Flux Method
Effective temperatures for 420 stars with spectral types between A0 andK3, and luminosity classes between II and V, selected for a fluxcalibration of the Infrared Space Observatory, ISO, have been determinedusing the Infrared Flux Method (IRFM). The determinations are based onnarrow and wide band photometric data obtained for this purpose, andtake into account previously published narrow-band measures oftemperature. Regression coefficients are given for relations between thedetermined temperatures and the photometric parameters (B2-V1), (b-y)and (B-V), corrected for interstellar extinction through use ofHipparcos parallaxes. A correction for the effect of metallicity on thedetermination of integrated flux is proposed. The importance of aknowledge of metallicity in the representation of derived temperaturesfor Class V, IV and III stars by empirical functions is discussed andformulae given. An estimate is given for the probable error of eachtemperature determination. Based on data from the ESA HipparcosAstrometry Satellite.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The [Fe/H] distribution of a volume limited sample of solar-type stars and its implications for galactic chemical evolution.
We present [Fe/H] determinations for a volume-limited sample of G and Kdwarfs from the Gliese catalog of nearby stars. The [Fe/H] values weredetermined from the FeI lines present in =~40Å wide highresolution (R >=50000) spectra taken around the LiI 6707.8Åline, through an equivalent width analysis based on the latest Kuruczmodel atmospheres. The resulting abundance distribution, corrected fordisk heating effects, is compared to recent models of galactic chemicalevolution. The surprising result is that, while the abundancedistribution of solar-type dwarfs hotter than =~5100K and the derivedchemical evolution parameters (in particular the rate of Fe enrichmentand the abundance spread at a given age) are compatible with previousdeterminations of the same quantities, dwarfs cooler than 5100K show alack of metal-poor ([Fe/H]<~-0.4) objects, implying chemicalevolution parameters (using the same model) not compatible with the onesderived for the hotter stars. Possible explanations for this fact arediscussed, critically considering possible biases present in the parentsample, as well as each of the assumptions made in the chemicalevolution model and in particular the assumption that the birth ratewill be constant with time and independent of stellar mass.
| The catalogue of nearby stars metallicities.
Not Available
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
Katalógusok és elnevezések:
|
INHABITED SKY
