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Resim Yükleyin
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Ýlgili Makaleler
A Uniform Analysis of 118 Stars with High-contrast Imaging: Long-period Extrasolar Giant Planets are Rare Around Sun-like Stars
We expand on the results of Nielsen et al., using the null result forgiant extrasolar planets around the 118 target stars from the Very LargeTelescope (VLT) NACO H- and Ks-band planet search (conducted byMasciadri and collaborators in 2003 and 2004), the VLT and MMTSimultaneous Differential Imager survey, and the Gemini Deep PlanetSurvey to set constraints on the population of giant extrasolar planets.Our analysis is extended to include the planet luminosity models ofFortney et al., as well as the correlation between stellar mass andfrequency of giant planets found by Johnson et al. Doubling the samplesize of FGKM stars strengthens our conclusions: a model for extrasolargiant planets with power laws for mass and semimajor axis as given byCumming et al. cannot, with 95% confidence, have planets beyond 65 AU,compared to the value of 94 AU reported by Nielsen et al., using themodels of Baraffe et al. When the Johnson et al. correction for stellarmass (which gives fewer Jupiter-mass companions to M stars with respectto solar-type stars) is applied, however, this limit moves out to 82 AU.For the relatively new Fortney et al. models, which predict fainterplanets across most of parameter space, these upper limits, with andwithout a correction for stellar mass, are 182 and 234 AU, respectively.
| 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.
| 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
| 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
| Constraints on Extrasolar Planet Populations from VLT NACO/SDI and MMT SDI and Direct Adaptive Optics Imaging Surveys: Giant Planets are Rare at Large Separations
We examine the implications for the distribution of extrasolar planetsbased on the null results from two of the largest direct imaging surveyspublished to date. Combining the measured contrast curves from 22 of thestars observed with the VLT NACO adaptive optics system by Masciadri andcoworkers and 48 of the stars observed with the VLT NACO SDI and MMT SDIdevices by Biller and coworkers (for a total of 60 unique stars), weconsider what distributions of planet masses and semimajor axes can beruled out by these data, based on Monte Carlo simulations of planetpopulations. We can set the following upper limit with 95% confidence:the fraction of stars with planets with semimajor axis between 20 and100 AU, and mass above 4 MJup, is 20% or less. Also, with adistribution of planet mass of dN/dM~M-1.16 in the range of0.5-13 MJup, we can rule out a power-law distribution forsemimajor axis (dN/da~aα) with index 0 and upper cutoffof 18 AU, and index -0.5 with an upper cutoff of 48 AU. For thedistribution suggested by Cumming et al., a power-law of index -0.61, wecan place an upper limit of 75 AU on the semimajor axis distribution. Ingeneral, we find that even null results from direct imaging surveys arevery powerful in constraining the distributions of giant planets (0.5-13MJup) at large separations, but more work needs to be done toclose the gap between planets that can be detected by direct imaging,and those to which the radial velocity method is sensitive.
| 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.
| An Imaging Survey for Extrasolar Planets around 45 Close, Young Stars with the Simultaneous Differential Imager at the Very Large Telescope and MMT
We present the results of a survey of 45 young (<~250 Myr), close(<~50 pc) stars with the Simultaneous Differential Imager (SDI)implemented at the VLT and the MMT for the direct detection ofextrasolar planets. As part of the survey, we observed 54 objects,consisting of 45 close, young stars; two more distant (<150 pc),extremely young (<=10 Myr) stars; three stars with known radialvelocity planets; and four older, very nearby (<=20 pc) solaranalogs. Our SDI devices use a double Wollaston prism and a quad filterto take images simultaneously at three wavelengths surrounding the 1.62μm methane absorption bandhead found in the spectrum of cool browndwarfs and gas giant planets. By differencing adaptive optics-correctedimages in these filters, speckle noise from the primary star issignificantly attenuated, resulting in photon (andflat-field)-noise-limited data. In our VLT data, we achieved H-bandcontrasts>~10 mag (5 σ) at a separation of 0.5" from theprimary star on 45% of our targets and H-band contrasts>~9 mag at aseparation of 0.5" on 80% of our targets. With these contrasts, we canimage (5 σ detection) a 7 MJ planet 15 AU from a 70 MyrK1 star at 15 pc or a 7.8 MJ planet at 2 AU from a 12 Myr Mstar at 10 pc. We detected no candidates with S/N>2 σ whichbehaved consistently like a real object. From our survey null result, wecan rule out (with 93% confidence) a model planet population whereN(a)~constant out to a distance of 45 AU.Steward Observatory, University of Arizona, Tucson, AZ 85721.
| Chemically Tagging the HR 1614 Moving Group
We present abundances for a sample of F, G, and K dwarfs of the HR 1614moving group based on high-resolution, high signal-to-noise ratiospectra from the Anglo-Australian Telescope UCLES instrument. Our sampleincludes stars from Feltzing and Holmberg, as well as from Eggen.Abundances were derived for Na, Mg, Al, Si, Ca, Mn, Fe, Ni, Zr, Ba, Ce,Nd, and Eu. The α, Fe, and Fe-peak element abundances show abimodal distribution, with four stars having solar metallicities, whilethe remaining 14 stars are metal-rich, [Fe/H]>=0.25 dex. However, theabundances of these two groups converge for the heavier n-captureelements. Based on their photometry and kinematics, three of the fourdeviating stars are likely nonmembers or binaries. Although one starcannot be excluded on these grounds, we do expect low-levelcontamination from field stars within the HR 1614 moving group's rangeof magnitude, color, and space velocities. Disregarding these fourstars, the abundance scatter across the group members for all elementsis low. We find that there is an 80% probability that the intrinsicscatter does not exceed the following values: Fe, 0.01 dex; Na, 0.08dex; Mg, 0.02 dex; Al, 0.06 dex; Si, 0.02 dex; Ca, 0.02 dex; Mn, 0.01dex; Ni, 0.01 dex; Zr, 0.03 dex; Ba, 0.03 dex; Ce, 0.04 dex; Nd, 0.01dex; and Eu, 0.02 dex. The homogeneity of the HR 1614 group in age andabundance suggests that it is the remnant of a dispersed star-formingevent. Its kinematical coherence shows that such a dispersing systemneed not be significantly perturbed by external dynamical influencessuch as Galactic spiral structure or giant molecular clouds, at leastover a period of 2 Gyr.
| Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters
We present a homogeneous set of stellar atmospheric parameters(Teff, logg, [Fe/H]) for MILES, a new spectral stellarlibrary covering the range λλ 3525-7500Å at2.3Å (FWHM) spectral resolution. The library consists of 985 starsspanning a large range in atmospheric parameters, from super-metal-rich,cool stars to hot, metal-poor stars. The spectral resolution, spectraltype coverage and number of stars represent a substantial improvementover previous libraries used in population synthesis models. Theatmospheric parameters that we present here are the result of aprevious, extensive compilation from the literature. In order toconstruct a homogeneous data set of atmospheric parameters we have takenthe sample of stars of Soubiran, Katz & Cayrel, which has very welldetermined fundamental parameters, as the standard reference system forour field stars, and have calibrated and bootstrapped the data fromother papers against it. The atmospheric parameters for our clusterstars have also been revised and updated according to recent metallicityscales, colour-temperature relations and improved set of isochrones.
| Accurate fundamental parameters for lower main-sequence stars
We derive an empirical effective temperature and bolometric luminositycalibration for G and K dwarfs, by applying our own implementation ofthe Infrared Flux Method to multiband photometry. Our study is based on104 stars for which we have excellent BV(RI)C JHKSphotometry, excellent parallaxes and good metallicities.Colours computed from the most recent synthetic libraries (ATLAS9 andMARCS) are found to be in good agreement with the empirical colours inthe optical bands, but some discrepancies still remain in the infrared.Synthetic and empirical bolometric corrections also show fair agreement.A careful comparison to temperatures, luminosities and angular diametersobtained with other methods in the literature shows that systematiceffects still exist in the calibrations at the level of a few per cent.Our Infrared Flux Method temperature scale is 100-K hotter than recentanalogous determinations in the literature, but is in agreement withspectroscopically calibrated temperature scales and fits well thecolours of the Sun. Our angular diameters are typically 3 per centsmaller when compared to other (indirect) determinations of angulardiameter for such stars, but are consistent with the limb-darkeningcorrected predictions of the latest 3D model atmospheres and also withthe results of asteroseismology.Very tight empirical relations are derived for bolometric luminosity,effective temperature and angular diameter from photometric indices.We find that much of the discrepancy with other temperature scales andthe uncertainties in the infrared synthetic colours arise from theuncertainties in the use of Vega as the flux calibrator. Angulardiameter measurements for a well-chosen set of G and K dwarfs would go along way to addressing this problem.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| Medium-resolution Isaac Newton Telescope library of empirical spectra
A new stellar library developed for stellar population synthesismodelling is presented. The library consists of 985 stars spanning alarge range in atmospheric parameters. The spectra were obtained at the2.5-m Isaac Newton Telescope and cover the range λλ3525-7500 Å at 2.3 Å (full width at half-maximum) spectralresolution. The spectral resolution, spectral-type coverage,flux-calibration accuracy and number of stars represent a substantialimprovement over previous libraries used in population-synthesis models.
| 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.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| Chromospheric Ca II Emission in Nearby F, G, K, and M Stars
We present chromospheric Ca II H and K activity measurements, rotationperiods, and ages for ~1200 F, G, K, and M type main-sequence stars from~18,000 archival spectra taken at Keck and Lick Observatories as a partof the California and Carnegie Planet Search Project. We have calibratedour chromospheric S-values against the Mount Wilson chromosphericactivity data. From these measurements we have calculated medianactivity levels and derived R'HK, stellar ages,and rotation periods from general parameterizations for 1228 stars,~1000 of which have no previously published S-values. We also presentprecise time series of activity measurements for these stars.Based on observations obtained at Lick Observatory, which is operated bythe University of California, and on observations obtained at the W. M.Keck Observatory, which is operated jointly by the University ofCalifornia and the California Institute of Technology. The KeckObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| 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
| 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.
| The Cosmic Production of Helium
We estimate the cosmic production rate of helium relative to metals(ΔY/ΔZ) using K dwarf stars in the Hipparcos catalog withaccurate spectroscopic metallicities. The best fitting value isΔY/ΔZ = 2.1 +/- 0.4 at the 68% confidence level. Our derivedvalue agrees with determinations from H II regions and with theoreticalpredictions from stellar yields with standard assumptions for theinitial mass function. The amount of helium in stars determines how longthey live and therefore how fast they will enrich the interstellarmedium with fresh material.
| 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
| 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.
| 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
| K dwarfs and the chemical evolution of the solar cylinder
K dwarfs have lifetimes older than the present age of the Galactic disc,and are thus ideal stars for investigating the chemical evolution of thedisc. We have developed several photometric metallicity indicators for Kdwarfs, based on a sample of accurate spectroscopic metallicities for 34disc and halo G and K dwarfs. The photometric metallicities lead us todevelop a metallicity index for K dwarfs based only on their position inthe colour-absolute-magnitude diagram. Metallicities have beendetermined for 431 single K dwarfs drawn from the Hipparcos catalogue,selecting the stars by absolute magnitude and removing multiple systems.The sample is essentially a complete reckoning of the metal content innearby K dwarfs. We use stellar isochrones to mark the stars by mass,and select a subset of 220 of the stars, which is complete within anarrow mass interval. We fit the data with a model of the chemicalevolution of the solar cylinder. We find that only a modest cosmicscatter is required to fit our age-metallicity relation. The modelassumes two main infall episodes for the formation of the halo-thickdisc and thin disc, respectively. The new data confirm that the solarneighbourhood formed on a long time-scale of the order of 7 Gyr.
| HIPPARCOS age-metallicity relation of the solar neighbourhood disc stars
We derive age-metallicity relations (AMRs) and orbital parameters forthe 1658 solar neighbourhood stars to which accurate distances aremeasured by the HIPPARCOS satellite. The sample stars comprise 1382 thindisc stars, 229 thick disc stars, and 47 halo stars according to theirorbital parameters. We find a considerable scatter for thin disc AMRalong the one-zone Galactic chemical evolution (GCE) model. Orbits andmetallicities of thin disc stars show now clear relation each other. Thescatter along the AMR exists even if the stars with the same orbits areselected. We examine simple extension of one-zone GCE models whichaccount for inhomogeneity in the effective yield and inhomogeneous starformation rate in the Galaxy. Both extensions of the one-zone GCE modelcannot account for the scatter in age - [Fe/H] - [Ca/Fe] relationsimultaneously. We conclude, therefore, that the scatter along the thindisc AMR is an essential feature in the formation and evolution of theGalaxy. The AMR for thick disc stars shows that the star formationterminated 8 Gyr ago in the thick disc. As already reported by Grattonet al. (\cite{Gratton_et.al.2000}) and Prochaska et al.(\cite{Prochaska_et.al.2000}), thick disc stars are more Ca-rich thanthin disc stars with the same [Fe/H]. We find that thick disc stars showa vertical abundance gradient. These three facts, the AMR, verticalgradient, and [Ca/Fe]-[Fe/H] relation, support monolithic collapseand/or accretion of satellite dwarf galaxies as likely thick discformation scenarios. Tables 2 and 3 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/ cgi-bin/qcat?J/ A+A/394/927
| 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.
| Catalogue of [Fe/H] determinations for FGK stars: 2001 edition
The catalogue presented here is a compilation of published atmosphericparameters (Teff, log g, [Fe/H]) obtained from highresolution, high signal-to-noise spectroscopic observations. This newedition has changed compared to the five previous versions. It is nowrestricted to intermediate and low mass stars (F, G and K stars). Itcontains 6354 determinations of (Teff, log g, [Fe/H]) for3356 stars, including 909 stars in 79 stellar systems. The literature iscomplete between January 1980 and December 2000 and includes 378references. The catalogue is made up of two tables, one for field starsand one for stars in galactic associations, open and globular clustersand external galaxies. The catalogue is distributed through the CDSdatabase. Access to the catalogue with cross-identification to othersets of data is also possible with VizieR (Ochsenbein et al.\cite{och00}). The catalogue (Tables 1 and 2) is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/373/159 and VizieRhttp://vizier.u-strasbg.fr/.
| 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
| Chemical abundances in cool metal rich disk dwarf stars
The present study of spectra of twelve metal-rich cool dwarf stars,carefully selected in order to cover a range of temperatures ( ~ 4400 -6000 K), is a follow up on Feltzing & Gustafsson(1998)\nocite{feltzing} with the aim to understand the apparentover-ionization and anomalous elemental abundances found by them for theK dwarf stars in their sample. Our method of analysis employs syntheticspectra of the full spectrum both to constrain the continuum level andto derive abundances. It is shown that by using this method and imposinga strict excitation equilibrium (possible to do because of the care inselection of observed Fe i lines) we are able to show that metal-rich Kdwarf stars do not show anomalous stellar abundances, as indicated inFeltzing & Gustafsson (1998), and can, with reasonable efforts, beanalyzed in order to increase the number of metal-rich stars with usefulchemical abundances. With abundance analysis by means of spectrumsynthesis and assuming Local Thermodynamic Equilibrium (LTE) theabundances of Na, Si, Ca, Sc, Ti, V, Cr, Fe, Co, Ni, and Nd have beenderived. Also ionization balance is satisfied for Fe and Cr aftercorrecting the stellar effective temperatures such that both ionizationand excitation equilibrium were satisfied. In addition, spectra fromfive cool dwarf stars of the Feltzing & Gustafsson (1998) samplehave been analyzed with the methods used in this work. They showessentially the same abundance patterns as the new stars in this sample.Based on observations made at ESO, La Silla}
| A statistical analysis of the metallicities of nine old superclusters and moving groups
Using both high-dispersion and low-resolution data, the metallicities ofnine old moving groups and superclusters are analyzed. These stellargroupings include the HR 1614 and Hyades superclusters and the Wolf 630,zeta Her, 61 Cyg, HR 1614, sigma Pup, eta Cep, and Arcturus groups.Samples of these stellar groupings are drawn from Eggen's membershiplists. Precautions are taken against problems posed by reddening, visualand spectroscopic binaries, and typographical errors in Eggen's lists.When required, the analyses allow for systematic differences betweenlow-resolution and high-dispersion metallicities. It is found that noneof the stellar groupings have the small metallicity dispersion found fora selection of galactic clusters. Instead, the metallicity dispersionsturn out to be comparable to the dispersion for a random selection offield stars. For most of the stellar groupings, it does not seempossible at present to learn more by analyzing metallicities. However,one can be more definite about three of them: the HR 1614 supercluster,the HR 1614 group, and the Hyades supercluster. Using a membership listfrom Eggen (\cite{e98c}) that is based on Hipparcos astrometry, noevidence is found for the existence of an HR 1614 supercluster. Toisolate an HR 1614 group, results from a kinematic analysis (Dehnen\cite{d98}) are then used to select a tentative list of members fromEggen's group and supercluster lists. From the mean metallicity of theredefined group, it is found that the group is very unlikely to be arandom, magnitude-limited sample of stars. A similar result is obtainedfor a version of the Hyades supercluster derived from 18 of Eggen'smembership lists. About 43% of the stars in this version turn out to bemembers of the supercluster.
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| Takýmyýldýz: | Guney Baligi |
| Sað Açýklýk: | 22h29m15.24s |
| Yükselim: | -30°01'06.2" |
| Görünürdeki Parlaklýk: | 7.658 |
| Uzaklýk: | 15.446 parsek |
| özdevim Sað Açýklýk: | 221.2 |
| özdevim Yükselim: | -808.2 |
| B-T magnitude: | 9.059 |
| V-T magnitude: | 7.774 |
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