Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| IRFM Teff calibrations for cluster and field giants in the Vilnius, Geneva, RI(C) and DDO photometric systems
Based on a large sample of disk and halo giant stars for which accurateeffective temperatures derived through the InfraRed Flux Method (IRFM)exist, a calibration of the temperature scale in the Vilnius, Geneva,RI_(C) and DDO photometric systems is performed. We provide calibrationformulae for the metallicity-dependent Teff vs. colorrelations as well as grids of intrinsic colors and compare them withother calibrations. Photometry, atmospheric parameters and reddeningcorrections for the stars of the sample have been updated with respectto the original sources to reduce the dispersion of the fits.Application of our results to Arcturus leads to an effective temperaturein excellent agreement with the value derived from its angular diameterand integrated flux. The effects of gravity on these Teff vs.color relations are also explored by taking into account our previousresults for dwarf stars.Based on data from the GCPD.
| The effects of age on red giant metallicities derived from the near-infrared CaII triplet
We have obtained spectra with a resolution of ~2.5 Å in the regionof ~7500-9500Å for 116 red giants in five galactic globularclusters and six old open clusters (five with published metallicitiesand one previously unmeasured). The signal-to-noise (S/N) ratio lieswithin the range 20 <= S/N <= 85. We measure the equivalent widthsof the infrared CaII triplet absorption lines in each star and comparethem with cluster metallicities taken from the literature. With globularcluster abundances on the Carretta & Gratton scale, and open clusterabundances taken from the compilation of Friel and collaborators, wefind a linear relation between [Fe/H] and CaII line strength spanningthe range -2 <~[Fe/H]<~-0.2 and 2.5 <~ (age/Gyr) <~ 13. Thereference abundance scales appear to be consistent with each other atthe ~0.1 dex level. Alternate choices for metallicity scales canintroduce curvature into the relation between the [Fe/H] and CaIIequivalent width. No evidence for an age effect on the metallicitycalibration is observed. Using this calibration, we find the metallicityof the massive, old, open cluster Trumpler 5 to be [Fe/H]=-0.56 +/-0.11. This is the first spectroscopic abundance measurement for Trumpler5, and is lower by ~0.3 dex than estimates based on the clustercolour-magnitude diagram. Considering the 10 clusters of knownmetallicity shifted to a common distance and reddening, we find that theadditional error introduced by the variation of horizontal branch/redclump magnitude with metallicity and age is of the order of +/-0.05 dex,which can be neglected in comparison with the intrinsic scatter in themethod. The results are discussed in the context of abundancedeterminations for red giants in Local Group galaxies.
| A high relative precision colour-magnitude diagram of M67
We have calibrated and combined an extensive set of BVI observations ofM67 to produce a colour-magnitude diagram of stars measured with highrelative precision. We have selected stars that are most likely to besingle-star members of the cluster using proper motion, radial velocity,and variability information from the literature, and an examination ofthe most probable colour-magnitude diagram locations of unresolvedstellar blends. We have made detailed comparisons of our photometry ofthe selected stars with theoretical models, and discuss the most notablediscrepancies. Observations of M67 turn-off stars are a severe test ofalgorithms attempting to describe convective cores in the limit of smallextent, and we find strong evidence of a `hook' just fainter than theturn-off gap. The stars in M67 support assertions that the degree ofconvective core overshooting decreases to zero for stars with masses inthe range 1.0 < (M/Msolar) <= 1.5, but that the degreeof overshoot is smaller than currently used in published isochrones. Wealso verify that all current theoretical models for the lower mainsequence (with the exception of Baraffe et al. 1998) are too blue forMV>~ 6, even when the sequences are shifted to match M67near the MV of the Sun, probably due to a combination ofproblems with colour-Teff transformations and realisticsurface boundary conditions for models. Finally, we identify a subset ofcluster members with unusual photometry (candidate red giant binaries,blue straggler stars, and triple systems) deserving of further study.
| CCD Photometry of the M 67 Cluster in the Vilnius System. II. New Photometry of High Accuracy
Seven color CCD photometry in the Vilnius system, supplemented by theCousins I passband, has been obtained for 412 stars down to V = 16 magin the M 67 open cluster area. A special method of flat-fielding, givinghigh accuracy photometry, was used. Photometric spectral types andinterstellar reddenings of all stars were determined. The mean reddeningof the cluster stars is EB-V = 0.04 mag and the distance is770 pc. Considerable systematic errors were found in some otherphotometric investigations of the same cluster.
| 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.
| Metallicities of Old Open Clusters
We present radial velocities and metallicities for a sample of 39 openclusters with ages greater than about 700 million years. For 24 clustersnew moderate-resolution spectroscopic data obtained with multiobjectspectrographs on the Kitt Peak National Observatory and the Cerro TololoInter-American Observatory 4 m telescopes are used to determine radialvelocities and mean cluster metallicities. These new results arecombined with data published previously by Friel & Janes to providea sample of 459 giants in 39 old open clusters, which are used toinvestigate radial abundance gradients in the Galactic disk. Based on anupdated abundance calibration of spectroscopic indices measuring Fe andFe-peak element blends, this larger sample yields an abundance gradientof -0.06+/-0.01 dex kpc-1 over a range in Galactocentricradius of 7 to 16 kpc. There is a slight suggestion of a steepening ofthe abundance gradient with increasing cluster age in this sample, butthe significance of the result is limited by the restricted distancerange for the youngest clusters. The clusters show no correlation ofmetallicity with age in the solar neighborhood. Consistent with theevidence for a steepening of the gradient with age, the clusters in theouter disk beyond 10 kpc show a suggestion at the 1.5 σ level of adependence of metallicity on age.
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is available in electronic form atthe 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/386/492, and from theauthors on CD-Rom.
| CCD photometry of RV-Tau type stars. Part 1. TT Ophiuchi.
Not Available
| Empirical calibration of the near-infrared Ca ii triplet - II. The stellar atmospheric parameters
We present a homogeneous set of stellar atmospheric parameters(Teff, logg, [Fe/H]) for a sample of about 700 field andcluster stars which constitute a new stellar library in the near-IRdeveloped for stellar population synthesis in this spectral region(λ8350-9020). Having compiled the available atmospheric data inthe literature for field stars, we have found systematic deviationsbetween the atmospheric parameters from different bibliographicreferences. The Soubiran, Katz & Cayrel sample of stars with verywell determined fundamental parameters has been taken as our standardreference system, and other papers have been calibrated and bootstrappedagainst it. The obtained transformations are provided in this paper.Once most of the data sets were on the same system, final parameterswere derived by performing error weighted means. Atmospheric parametersfor cluster stars have also been revised and updated according to recentmetallicity scales and colour-temperature relations.
| Accurate Vsin i measurements in M 67: The angular momentum evolution of 1.2 Msun stars
By using FEROS spectrograph commissioning observations, we build acalibration of the FEROS cross-correlation function (CCF) to determineaccurate projected rotational velocities Vsin i for slow rotating F-Kdwarf and giant stars. We apply this calibration to a sample of 28 mainsequence, turnoff and giant stars belonging to the old open cluster M67. We find that the stars behave in a very regular manner, depending ontheir position in the Color-Magnitude (C-M) diagram. Early main sequenceG stars have a rotational velocity two times larger than the Sun, andthey show a possible trend with (B-V) color, in that redder colorscorrespond to lower Vsin i. The stars at the turnoff are the fastestrotators, with Vsin i between 6.3 and 7.6 km s-1, while starsjust above the turn-off are already significantly slower , with valuesbetween 4.6 and 4.9 km s-1. Along the Red Giant Branch (RGB),rotation decreases smoothly and for stars above (B-V)ga1 , only upperlimits can be found, including for 4 clump stars. Analyzing the angularmomentum history of 1.2 Msun stars with the help oftheoretical evolutionary tracks, we see that these stars probably obeydifferent angular momentum evolution laws on the main sequence and alongthe RGB: while on the main sequence some extra braking is required inaddition to angular momentum conservation, along the RGB the data arewell represented by the IOmega =C law. Finally, comparing the Vsin i ofthe M 67 turnoff stars with their main sequence progenitors in theyounger open clusters NGC 3680 and Hyades we find that the youngerclusters show substantially higher rotation rates. This indicates that1.2 Msun stars do experience main sequence braking. Thiscould be relevant also for the interpretation of the nature of the``Lithium gap''. Based on observations collected at ESO, La Silla.
| The Metallicity Distribution Function of Red Giants in the Large Magellanic Cloud
We report new metallicity determinations for 39 red giants in a 220arcmin2 region, 1.8d southwest of the bar of the LargeMagellanic Cloud. These abundance measurements are based on spectroscopyof the Ca II infrared triplet. We have carefully considered the effectsof abundance ratios, the physics of Ca II line formation, the variationof red clump magnitude, and the contamination by foreground stars in ourabundance analyses. The metallicity distribution function (MDF) shows astrong peak at [Fe/H]=-0.57+/-0.04 a tail to abundances at least as lowas [Fe/H]~-1.6 brings the average abundance down to [Fe/H]=-0.64+/-0.02.Half the red giants in our field fall within the range-0.83<=[Fe/H]<=-0.41. The MDF appears to be truncated at[Fe/H]~-0.25 the exact value of the maximum abundance is subject to ~0.1dex uncertainty in the calibration of the Ca II IR triplet for young,metal-rich stars. We find a striking contrast in the shape of the MDFbelow [Fe/H]<=-1 between our inner disk field and the distant outerfield studied by Olszewski: red giants deficient by more than a factorof 10 in heavy elements relative to the Sun are extremely scarce in theinner disk of the LMC. Our field star sample does not reproduce the fullMDF of the LMC star clusters but seems similar to that of theintermediate-age (1-3 Gyr) clusters. We have also obtained abundanceestimates using Strömgren photometry for ~103 red giantsin the same field. Photometry is the only practical way to measureabundances for the large numbers of stars necessary to liftage-metallicity degeneracy from our high-precision color-magnitudediagrams. The Strömgren measurements, which are sensitive to acombination of cyanogen and iron lines, correlate well with the Ca IImeasurements, but a metallicity-dependent offset is found. The offsetmay be due either to variations in the elemental abundance ratios due togalactic chemical evolution or to a metal-dependent mixing mechanism inRGB stars. An empirical relation between photometric and spectroscopicabundance estimates is derived. This will allow photometric abundancemeasurements to be placed on a consistent metallicity scale withspectroscopic metallicities, for very large numbers of stars. Based onobservations obtained at Cerro Tololo Inter-American Observatory, adivision of the National Optical Astronomy Observatories, which areoperated by the Association of Universities for Research in Astronomy,Inc. under cooperative agreement with the National Science Foundation.
| 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
| The effective temperature scale of giant stars (F0-K5). III. Stellar radii and the calibration of convection
We present an analysis of radii of giant stars with 6200 K>= T_eff>= 3800 K based on angular diameters obtained by means of the IRFMand distances computed from Hipparcos parallaxes. In order to asses thereliability of IRFM diameters we have considered a selected sample ofstars whose diameters have been directly measured by interferometrictechniques with internal errors below 5%. The intercomparison shows afairly good consistency and no systematic differences againsttemperature are apparent in the analysis. By averaging the individualvalues obtained for a sample of approximately 300 stars, we present meanvalues of linear radii of giants of solar metallicity; the results aretentatively extended to metal-poor giants. We have also devised a methodto derive distance moduli of globular clusters complementary to thestandard Main Sequence (MS) and Horizontal Branch (HB) fitting. Thismethod is based on the fit of observed linear radii and effectivetemperatures of Red Giant Branch stars of a given globular cluster tothe yields of theoretical isochrones. A careful assessment of theuncertainty on the derived distances is provided. As expected, thedistances are critically dependent on the value of the mixing lengthparameter adopted in the stellar models. We have applied the method toprovide a homogeneous distance scale for a representative sample ofGalactic globular clusters. The comparison of these distances with thedistance scale obtained by means of the MS- or HB-fitting permits aconsistent calibration and/or test of the superadiabatic gradient instellar envelopes, independent of the use of colour-T_efftransformations.
| The effective temperature scale of giant stars (F0-K5). I. The effective temperature determination by means of the IRFM
We have applied the InfraRed Flux Method (IRFM) to a sample ofapproximately 500 giant stars in order to derive their effectivetemperatures with an internal mean accuracy of about 1.5% and a maximumuncertainty in the zero point of the order of 0.9%. For the applicationof the IRFM, we have used a homogeneous grid of theoretical modelatmosphere flux distributions developed by \cite[Kurucz (1993)]{K93}.The atmospheric parameters of the stars roughly cover the ranges: 3500 K<= T_eff <= 8000 K; -3.0 <= [Fe/H] <= +0.5; 0.5 <= log(g) <= 3.5. The monochromatic infrared fluxes at the continuum arebased on recent photometry with errors that satisfy the accuracyrequirements of the work. We have derived the bolometric correction ofgiant stars by using a new calibration which takes the effect ofmetallicity into account. Direct spectroscopic determinations ofmetallicity have been adopted where available, although estimates basedon photometric calibrations have been considered for some stars lackingspectroscopic ones. The adopted infrared absolute flux calibration,based on direct optical measurements of stellar angular diameters, putsthe effective temperatures determined in this work in the same scale asthose obtained by direct methods. We have derived up to fourtemperatures, TJ, TH, TK and T_{L'},for each star using the monochromatic fluxes at different infraredwavelengths in the photometric bands J, H, K and L'. They show goodconsistency over 4000 K, and there is no appreciable trend withwavelength, metallicity and/or temperature. We provide a detaileddescription of the steps followed for the application of the IRFM, aswell as the sources of error and their effect on final temperatures. Wealso provide a comparison of the results with previous work.
| Empirical calibration of the lambda 4000 Å break
Empirical fitting functions, describing the behaviour of the lambda 4000Ä break, D4000, in terms of effective temperature,metallicity and surface gravity, are presented. For this purpose, thebreak has been measured in 392 stars from the Lick/IDS Library. We havefollowed a very detailed error treatment in the reduction and fittingprocedures, allowing for a reliable estimation of the breakuncertainties. This calibration can be easily incorporated into stellarpopulation models to provide accurate predictions of the break amplitudefor, relatively old, composite systems. Table 1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Evolution of Chromospheric Activity: M67 Red Giants
Echelle spectra of the Ca II H- and K-line region (lambda3950) of 15 redgiant stars in the open cluster M67 reveal atmospheric dynamics anddetermine chromospheric radiative losses in order to assesschromospheric heating requirements and to follow the evolution ofchromospheric activity. M67 red giants in conjunction with giants inyounger clusters create a continuous group of red giants in thecolor-magnitude diagram, with 0.1<=(B-V)<=1.65 along the red giantbranch. M67 contains the more evolved clump giants as well. Asymmetricline emission cores, indicative of outflowing material, are found in amajority of the M67 giants on the red giant branch and occur over thecomplete sample, from M_V=-0.8 to M_V=1.9, suggesting that outward massmotions are well established at these luminosities. Radiative losses, asmeasured by emission strengths from Ca II, decrease smoothly withdecreasing stellar effective temperature in M67 and connect well to acombined sample of warmer cluster giants (NGC 2477, IC 4756, and theHyades) with M<=3 M_solar studied by Beasley & Cram. Stellareffective temperature predominantly determines the level ofchromospheric Ca II losses for giants with M<=3 M_solar. No evidenceis found for a sharp decline in the flux of Ca II predicted by theRutten & Pylyser magnetic model for chromospheric heating. However,emission in field giants (which tend to be younger) suggests that sharpdeclines in surface flux with decreasing effective temperaturecharacteristic of pure magnetic activity occur for ion species morehighly excited than Ca II. Although acoustic models for chromosphericheating apparently agree with the measured Ca II flux levels for thecoolest giants, additional heating processes must be present in warmergiants and clump stars. Clump giants exhibit Ca II fluxes consistentwith stars of similar colors on the red giant branch, suggesting arenaissance in chromospheric heating occurs after evolution beyond thered giant branch. Chromospheric heating in the giants of solarmetallicity is likely to be derived from multiple sources, bothhydrodynamic causes as well as magnetically related processes. Therelative contribution of each heating mechanism changes with temperaturein the stellar atmosphere, and these proportions may change during astar's evolution from the main sequence.
| Photometric Separation of Stellar Properties Using SDSS Filters
Using synthetic photometry of Kurucz model spectra, we explore thecolors of stars as a function of temperature, metallicity, and surfacegravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. Thesynthetic colors show qualitative agreement with the few publishedobservations in these filters. We find that the locus of synthetic starsis basically two-dimensional for 4500 < T < 8000 K, whichprecludes simultaneous color separation of the three basic stellarcharacteristics we consider. Colors including u' contain the mostinformation about normal stellar properties; measurements in this filterare also important for selecting white dwarfs. We identify two differentsubsets of the locus in which the loci separate by either metallicity orsurface gravity. For 0.5 < g' - r' < 0.8 (corresponding roughly toG stars), the locus separates by metallicity; for photometric error of afew percent, we estimate metallicity to within ~0.5 dex in this range.In the range -0.15 < g' - r' < 0.00 (corresponding roughly to Astars), the locus shows separation by surface gravity. In both cases, weshow that it is advantageous to use more than two colors whendetermining stellar properties by color. Strategic observations in SDSSfilters are required to resolve the source of a ~5% discrepancy betweensynthetic colors of Gunn-Stryker stars, Kurucz models, and externaldeterminations of the metallicities and surface gravities. The syntheticstar colors can be used to investigate the properties of any normal starand to construct analytic expressions for the photometric prediction ofstellar properties in special cases.
| CCD Photometry of the M 67 Cluster in the Vilnius Photometric System
Seven-color CCD photometry in the Vilnius photometric system of 279stars down to V = 15 mag in the open cluster M 67 area is obtained. 13standard stars in the cluster are measured photoelectrically.Photometric spectral types have been determined for all the stars. Thereddening of the cluster is found to be E_{B-V} = 0.045, the truedistance modulus is 9.38 mag and the age is 4times 10(9) years.
| The Mount Wilson Halo Mapping Project 1975-1985 I: The UBV(RI)_M_W Photometric System Compared with Other Standard Systems: The Adopted Trigonometric HR Diagram in (R-I)_M_W and (V-I)_M_W
Photometry of stars is described that defines a UBV(RI)_M_W photometricsystem, established between 1975 and 1980 using the Mount Wilson 60-inchand 100-inch reflectors. The MW natural system has been reduced to theUBV(RI)_C Cape-Cousins system by linear equations for stars hotter thanM0. Strong non-linear color and magnitude equations exit in R and Ibetween the two systems for stars cooler than M0. The non-linearity isdue to the change of the effective wavelengths of the red passbandscaused by effect of the TiO b ands combines with the substantialdifference between red response of the extended S20 cathodes used hereand the GaAs cells used by Cousins (1976, 1980a,b), Bessell (1979,1990), Landolt (1983, 1992), and others for the Cape system. We report(R-I)_M_W and (V-I)_M_W colors based on a linear extension of the _M_Wnatural system to the red for cool stars with (V-R)_Cape greater than0.8, (V-I)_Cape greater than 1.8 (spectral types later than M0), aszero-pointed to the Cape system for bluer stars. Color equations arederived between the MW, the Cape, the Kron-Eggen, and Johnsonphotometric systems, and also the Hubble Space Telescope (V-I) colors asreduced to the (V-I)_C Cape system by Holtzman et al. (1995). TheKron-Eggen and the Cape-Cousins R and I systems differ in their zeropoints of color and magnitudes, showing that the Kron-Eggen and theCousins systems are not the same. The appellation of a "Kron-Cousins"photometric system used in much of the current literature is incorrect.Preparatory to determining photometric parallaxes of local higher propermotion M dwarfs in Paper IV, trigonometric HR diagrams are determined inV, (V-R)_M_W and (V-I)_M_W on the Mount Wilson system using 160available parallax stars with parallaxes larger than 0.099 arcsec. Afirst appendix illustrates the difference in the effective wavelengthsof the Cape-Cousins, Kron-Eggen, and Johnson systems for cool stars,based on the observed slope coefficients of the color equations thatlink them. A second appendix contains explicit color equations based onstars in common between Bessell's (1990) definition of the Cape systemfor the reddest stars and the Kron-Eggen and the MW photometric systems.(SECTION: Stars)
| H gamma and H delta Absorption Features in Stars and Stellar Populations
The H gamma and H delta absorption features are measured in a sample of455 (out of an original 460) Lick/IDS stars with pseudo--equivalentwidth indices. For each Balmer feature, two definitions, involving anarrow (~20 Angstroms) and a wide (~40 Angstroms) central bandpass, aremeasured. These four new Balmer indices augment 21 indices previouslydetermined by Worthey et al., and polynomial fitting functions that giveindex strengths as a function of stellar temperature, gravity, and[Fe/H] are provided. The new indices are folded into models for theintegrated light of stellar populations, and predictions are given forsingle-burst stellar populations of a variety of ages and metallicities.Contrary to our initial hopes, the indices cannot break a degeneracybetween burst age and burst strength in post-starburst objects, but theyare successful mean-age indicators when used with sensitive metallicityindicators. An appendix gives data, advice, and examples of how totransform new spectra to the 25-index Lick/IDS system.
| 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
| Spectral Classification of "Photometric Subgiants" in Open Clusters
Color-magnitude diagrams of several intermediate-age open clusterscontain apparent post-main-sequence stars which are fainter thanpredicted by standard evolutionary tracks. We have obtainedclassification spectra for such stars in eight clusters. Some of theseare reddened background early-type stars, and several of the late-typestars turn out to have luminosities indicative of being foreground tothe cluster. A few stars appear to be cluster members but do not fit thetheoretical tracks. We find that the Bahcall-Soneira Galaxy model,modified for low galactic latitudes, can give statistically usefulpredictions of the numbers of field stars.
| Deep Wide-Field Spectrophotometry of the Open Cluster M67
We present nine color CCD intermediate-band spectrophotometry of a twosquare degree field centered on the old open cluster M67, from 3890$\rm\AA$ to nearly 1$\mu$. These observations are taken as a part of theBATC (Beijing-Arizona-Taipei-Connecticut) Color Survey of the Sky, forboth scientific and calibration reasons. With these data we show thatthe BATC survey can reach its goal of obtaining spectrophotometry to azero point accuracy of 0.01 mag, and down to V = 21 with 0.3 mag randomerror. We fit the color-magnitude diagrams (CMDs) with Worthey'stheoretical models. The net result is the excellent fit of the 4.0 Gyr,[Fe/H] = $-0.10$ model to our data, including a good fit to the mainsequence (MS) turn-off. Our data are consistent with a toy model with50\% of the stars in M67 being binaries and a random distribution ofbinary mass-ratios, although other models with different mass-ratiodistributions cannot be ruled out. The spatial distribution and massfunction (MF) of stars in M67 show marked effects of dynamical evolutionand evaporation of stars from the cluster. Blue stragglers and binarystars are the most condensed within the cluster, with degree ofcondensation depending on mass.We find M67 to have an elongated shape,oriented at an angle of $15^{\circ}$ relative to the galactic plane.Within its tidal radius, the observed MF of M67 between 1.2 $\rmM_\odot$ and $\rm 0.8 M_\odot$ has a Salpeter slope $\rm \eta = -1.93\pm 0.66$. For stars of mass below 0.8 $\rm M_\odot$, $\rm \eta \sim 0$.It is plausible that the leveling-off of the MF at lower masses is aresult of evaporation of lower mass stars in this mass range at a rateof one every $\sim 10^7$ years. If so, it is plausible that the IMF ofM67 has the canonical field value of $\rm \eta = -2.0$.
| Age and Abundance Effects in Single-Stellar Populations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2408B&db_key=AST
| The Lithium Dip in M67: Comparison with the Hyades, Praesepe, and NGC 752 Clusters
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...446..203B&db_key=AST
| Kinematics of the old open cluster system
Radial velocities accurate to 15 km/s or better were determined for 11open clusters older than approximately 1 GYR and distributed over arange of positions in the galaxy. Moderate resolution spectra of anaverage of 30 stars in each cluster of varying spectral types wereobtained using the 4.0 m telescope at Kitt Peak National Observatory(KPNO) and the Hydra multi-object spectrograph. The radial velocitieswere calculated for the late type giants in each cluster using crosscorrelation techniques; and mean velocity values were obtained for fiveclusters with no previous radial velocity measurements: Be 17, Be 31, Be32, King 5, and King 11. Using these data, along with publishedvelocities for an additional 24 clusters, the mean difference betweenthe velocities of the open clusters and those predicted by a standaredrotation curve is 1 +/- 29 km/s. Also, assuming that the old opencluster system rotates about the Galactic center with a constantrotation velocity, this velocity is found to be 21 +/- 7 km/s with aline-of-sight dispersion of 28 km/s. Both of these results imply thatthe old open clusters are predominantly a thin disk population. Be 17,the oldest cluster in this sample, also exhibits peculiar kinematics,and is discussed in particular.
| Tidal circularization and the eccentricity of binaries containing giant stars.
We show that the predicted amount of tidal circularization in a detachedbinary containing a giant is, according to Zahn's theory, determinedonly by observable properties of its orbit, and a single integral alongthe giant's stellar evolutionary sequence. We perform these integrals,display them graphically, and provide fitting formulae. Spectroscopicbinaries in open clusters are ideal for testing the theory of tidalcircularization, since the stars' mass, luminosity and temperature canall be determined with precision. We apply our calculations to 28binaries in 12 open clusters. We show that the orbital parameters of allcan be understood within the circularization theory, and that the mixinglength parameter in Zahn's theory is well constrained:1<~α<~3. We show that the orbital period alone does notseparate circular and eccentric orbits, and point out that theeccentricity of the orbit can sometimes distinguish between giant starsand core helium burning `clump' stars even in circumstances where thisis difficult spectroscopically. In some special types of binary systems,the circularization is sensitive to aspects of stellar evolution theorythat are not well understood: the maximum depth of penetration of theouter convective zone, the radius at first dredge-up, the maximum radiiof stars at the tips of the giant and asymptotic giant branches. It thusappears that the orbits of binaries containing giants may prove to be auseful tool for studying stellar evolution.
| Old stellar populations. 5: Absorption feature indices for the complete LICK/IDS sample of stars
Twenty-one optical absorption features, 11 of which have been previouslydefined, are automatically measured in a sample of 460 stars. FollowingGorgas et al., the indices are summarized in fitting functions that giveindex strengths as functions of stellar temperature, gravity, and(Fe/H). This project was carried out with the purpose of predictingindex strengths in the integrated light of stellar populations ofdifferent ages and metallicities, but the data should be valuable forstellar studies in the Galaxy as well. Several of the new indices appearto be promising indicators of metallicity for old stellar populations. Acomplete list of index data and atmospheric parameters is available incomputer-readable form.
| Optical identification of two soft ROSAT sources in the old open cluster M67
We have obtained low-resolution spectra of two soft ROSAT sources in thefield of the old (~4 Gyrs) open cluster M67. One of the sources is an AMHer type cataclysmic variable (CV), and the other is a weak-lined DAwhite dwarf (WD). Both sources are located in the central region of M67and they are probable members of the cluster. The AM Her is the firstspectroscopically confirmed AM Her system found associated with an opencluster and the WD is the only degenerate star known in M67.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Рак |
| Прямое восхождение: | 08h51m29.91s |
| Склонение: | +11°47'16.9" |
| Видимая звёздная величина: | 9.762 |
| Собственное движение RA: | -7.2 |
| Собственное движение Dec: | -6.2 |
| B-T magnitude: | 11.584 |
| V-T magnitude: | 9.913 |
Каталоги и обозначения:
|
