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Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| The PASTEL catalogue of stellar parameters
Aims: The PASTEL catalogue is an update of the [Fe/H] catalogue,published in 1997 and 2001. It is a bibliographical compilation ofstellar atmospheric parameters providing (T_eff, log g, [Fe/H])determinations obtained from the analysis of high resolution, highsignal-to-noise spectra, carried out with model atmospheres. PASTEL alsoprovides determinations of the one parameter T_eff based on variousmethods. It is aimed in the future to provide also homogenizedatmospheric parameters and elemental abundances, radial and rotationalvelocities. A web interface has been created to query the catalogue onelaborated criteria. PASTEL is also distributed through the CDS databaseand VizieR. Methods: To make it as complete as possible, the mainjournals have been surveyed, as well as the CDS database, to findrelevant publications. The catalogue is regularly updated with newdeterminations found in the literature. Results: As of Febuary2010, PASTEL includes 30151 determinations of either T_eff or (T_eff,log g, [Fe/H]) for 16 649 different stars corresponding to 865bibliographical references. Nearly 6000 stars have a determination ofthe three parameters (T_eff, log g, [Fe/H]) with a high qualityspectroscopic metallicity.The catalogue can be queried through a dedicated web interface at http://pastel.obs.u-bordeaux1.fr/.It is also available in electronic form at the Centre de DonnéesStellaires in Strasbourg (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/pastel),at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A111
| Mg and TiO spectral features at the near-IR: spectrophotometric index definitions and empirical calibrations
Using the near-infrared spectral stellar library of Cenarro et al., thebehaviour of the MgI line at 8807 Å and nearby TiO bands isanalyzed in terms of the effective temperature, surface gravity andmetallicity of the library stars. New spectroscopic indices for bothspectral features - namely MgI and sTiO - are defined, and theirsensitivities to different signal-to-noise ratios, spectral resolutions,flux calibrations and sky emission-line residuals are characterized. Thetwo new indices exhibit interesting properties. In particular, MgI is agood indicator of the Mg abundance, whereas sTiO is a powerfuldwarf-to-giant discriminator for cold spectral types. Empirical fittingpolynomials that reproduce the strength of the new indices as a functionof the stellar atmospheric parameters are computed, and a FORTRANroutine with the fitting function predictions is made available. Athorough study of several error sources, non-solar [Mg/Fe] ratios andtheir influence on the fitting function residuals is also presented.From this analysis, an [Mg/Fe] underabundance of ~ -0.04 is derived forthe Galactic open cluster M67.
| Membership, binarity, and rotation of red dwarfs in the nearby open cluster Coma Berenices (Melotte 111)
Context: Although several attempts have been made to identify solar-typemembers on the main sequence of the nearby open cluster Coma Berenices(Mel 111), the population of the lower main sequence is still poorlyknown. Aims: We observed 46 new candidates to search for new membersand monitored known spectroscopic-binary members to determine orbitalparameters. Methods: We obtained a total of 903 radial-velocitymeasurements of 69 solar-type stars in the field of Mel 111 with theCORAVEL spectrovelocimeter over 20 years. Results: Among the 35 starsfrom Trumpler's list, 23 are members according to their radialvelocities and photometry. We were able to confirm the membership ofonly 8 stars among the 46 candidates observed. Six double-lined and tensingle-lined spectroscopic binaries were discovered. Six only aremembers and an orbit was determined for them and for 4 double-linednon-members. The binary frequency is 22% (7/32). The cluster mean radialvelocity is +0.01 ± 0.08 km s-1 based on 28 members. Conclusions: The lower main sequence of the Coma Berenices open clusteris still rather poorly populated. The cluster size may be much largerthat usually accepted. Accordingly extensive programmes to determineprecise proper motions, radial velocities and photometry should beundertaken to identify faint cluster members outside the cluster centralarea. If a significant population of faint members cannot be identified,Coma Ber could be a prominent example of dynamical evolution leading tostar evaporation.Based on observations collected at the Haute-Provence Observatory(France). Table 1 is also available, and Full Table 8 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/491/951
| The Stellar Populations of Praesepe and Coma Berenices
We present the results of a stellar membership survey of the nearby openclusters Praesepe and Coma Berenices. We have combined archival surveydata from the SDSS, 2MASS, USNOB1.0, and UCAC-2.0 surveys to compileproper motions and photometry for ~5 million sources over 300deg2. Of these sources, 1010 stars in Praesepe and 98 starsin Coma Ber are identified as candidate members with probability >80%442 and 61 are identified as high-probability candidates for the firsttime. We estimate that this survey is >90% complete across a widerange of spectral types (F0-M5 in Praesepe, F5-M6 in Coma Ber). We havealso investigated the stellar mass dependence of each cluster's mass andradius in order to quantify the role of mass segregation and tidalstripping in shaping the present-day mass function and spatialdistribution of stars. Praesepe shows clear evidence of mass segregationacross the full stellar mass range; Coma Ber does not show any cleartrend, but low number statistics would mask a trend of the samemagnitude as in Praesepe. The mass function for Praesepe (? ~ 600Myr; M ~ 500 Modot) follows a power law consistent with thatof the field present-day mass function, suggesting that anymass-dependent tidal stripping could have removed only the lowest massmembers (<0.15 Modot). Coma Ber, which is younger but muchless massive (? ~ 400 Myr; M ~ 100 Modot), follows asignificantly shallower power law. This suggests that some tidalstripping has occurred, but the low-mass stellar population has not beenstrongly depleted down to the survey completeness limit (~0.12Modot).
| New stellar members of the Coma Berenices open star cluster
We present the results of a survey of the Coma Berenices open starcluster (Melotte 111), undertaken using proper motions from theUSNO-B1.0 (United States Naval Observatory) and photometry from theTwo-Micron All-Sky Survey (2MASS) Point Source catalogues. We haveidentified 60 new candidate members with masses in the range 1.007
| Chemical composition of red horizontal branch stars in the thick disk of the Galaxy
High-resolution spectra of 13 core helium-burning stars in the thickdisk of the Galaxy have been obtained with the SOFIN spectrograph on theNordic Optical Telescope to investigate abundances of up to 22 chemicalelements. Abundances of carbon were studied using the C2 Swan(0, 1) band head at 5635.5 Å. The wavelength interval 7980-8130Å with strong CN features was analysed in order to determinenitrogen abundances and 12C/13C isotope ratios.The oxygen abundances were determined from the [O I] line at 6300Å. Abundances in the investigated stars suggest that carbon isdepleted by about 0.3 dex, nitrogen is enhanced by more than 0.4 dex andoxygen is unaltered. The 12C/13C ratios arelowered and lie between values 3 and 7 which is in agreement with ``coolbottom processing'' predictions (Boothroyd & Sackmann 1999). The C/Nratios in the investigated stars are lowered to values between 0.7 and1.2 which is less than present day theoretical predictions and call forfurther studies of stellar mixing processes. Abundance ratios of O, Mg,Eu and other heavy chemical elements to iron in the investigated starsshow a pattern characteristic of thick disk stars. The results provideevidence that the thick disk population has a distinct chemical historyfrom the thin disk. The onset of the bulk of SN Ia is suggested toappear at [Fe/H] ~ -0.6 dex. Based on observations obtained at theNordic Optical Telescope, La Palma. Table 1 is only available inelectronic 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/380/578
| 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.
| 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
| An astrometric catalogue for the area of Coma Berenices
A catalogue of stellar positions and proper motions down to the 14thphotographic magnitude in the area of the open cluster in Coma Berenicesis compiled from data of 12 different sources. The accuracy of theproper motion data is comparable to that of the Hipparcos Catalogue. Thecatalogue Table 5 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/Abstract.html
| Radial Velocities of Population II Stars. II.
A program for radial velocity measurements of Population II stars wasstarted in 1988 and was carried out during six observing runs. Theprogram includes metal-deficient stars, components of Population IIvisual binaries or common proper motion stars, suspected radial velocityvariables and the Population II stars from the Hipparcos program. Themeasurements were made with the 1 meter reflector at the MaidanakObservatory in Uzbekistan. The average error of a single measurement isabout 0.6 km/s, but for stars at 13 mag or for extremely metal-deficientstars the error is about 2.5 km/s. The catalog contains 621 measurementsfor 164 stars.
| Classification of Population II Stars in the Vilnius Photometric System. II. Results
The results of photometric classification of 848 true and suspectedPopulation II stars, some of which were found to belong to Population I,are presented. The stars were classified using a new calibrationdescribed in Paper I (Bartkevicius & Lazauskaite 1996). We combinethese results with our results from Paper I and discuss in greaterdetail the following groups of stars: UU Herculis-type stars and otherhigh-galactic-latitude supergiants, field red horizontal-branch stars,metal-deficient visual binaries, metal-deficient subgiants, stars fromthe Catalogue of Metal-deficient F--M Stars Classified Photometrically(MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs(Bartkevicius 1994a). It is confirmed that high galactic latitudesupergiants from the Bartaya (1979) catalog are giants or even dwarfs.Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as fieldRHB stars, appear to be ordinary giants according to our classification.Some of the visual binaries studied can be considered as physical pairs.Quite a large fraction of stars from the MDPH catalog are found to havesolar metallicity. A number of new possible UU Herculis-type stars, RHBstars and metal-deficient subgiants are identified.
| Vilnius photometry of the red horizontal branch stars in the galactic thick disk
The photometric observations and three-dimensional classification in theVilnius system have been carried out for 13 of the red horizontal branch(RHB) stars in the Galactic thick disk identified by Rose (1985). Thephotometric spectral types, metallicities [Fe/H], effectivetemperatures, surface gravities and absolute magnitudes are determined.The age of about 10--12 Gyr is evaluated for this group of stars fromcomparison with model isochrones, indicating that the age of the thickdisk is intermediate between the disk globular and the oldest openclusters.
| Radial velocities of Population II stars. I
Radial velocity measurements are presented for 81 Population II stars.The sample comprises components of metal-poor binary stars,spectroscopic binary candidates, high latitude supergiants,metal-deficient stars with spectroscopic determinations of Fe/H,HIPPARCOS program stars, and some other stars of metal-poor population.The radial velocity measurements were made in February 1988 with aphotoelectric stellar velocimeter.
| New carbon stars found in a hemispheric survey
105 new, cool galactic carbon stars are listed, found in 11 years ofobjective-prism surveys covering upwards of 25000 deg2(almost all) north of declination -25°. The stars are mostlybrighter than visual magnitude 13.5.
| Photoelectric Studies. III. Color-Luminosity Arrays for the Coma Berenices and Ursa Major Clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1950ApJ...111..414E&db_key=AST
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Волосы Вероники |
| Прямое восхождение: | 12h24m17.15s |
| Склонение: | +24°19'28.4" |
| Видимая звёздная величина: | 9.922 |
| Собственное движение RA: | -16.1 |
| Собственное движение Dec: | -12.1 |
| B-T magnitude: | 10.865 |
| V-T magnitude: | 10 |
Каталоги и обозначения:
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