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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.
| Photometric membership and metallicities of red giant candidates in selected open clusters
As part of a long-term project to determine abundances andastrophysical properties of evolved red stars in open clusters, wepresent high-precision DDO photoelectric observations for a sample of 33red giant candidates projected in the fields of nine Galactic openclusters. These data are supplemented with U BV photoelectric photometryof 24 of these stars as well as with CORAVEL radial-velocityobservations for 13 red giant candidates in four of the clusters. Wealso present Washington photoelectric photometry of a small sample ofred giant candidates of the open cluster Ruprecht 97. The likelihood ofcluster membership for each star photometrically observed and for 23additional red giant candidates with U BV and DDO data available in theliterature, is evaluated by using two independent photometric criteria.Nearly 82% of the analysed stars are found to have a high probability ofbeing cluster giants. Photometric membership probabilities show verygood agreement with those obtained from CORAVEL radial velocities. WhileE(B-V) colour excesses were determined from combined B-V and DDOcolours, calibrations of the DDO system were used to derive MK spectraltypes, effective temperatures and metallicities.The derived DDOmetallicities range between values typical of moderately metal-poorclusters ([Fe/H] = -0.19) to moderately metal-rich ([Fe/H] = 0.25) ones.Tables 3, 4, 7-9 are available at the CDS viahttp://cdsarc.u-strasbg.fr/cgi-bin/qcat?J/AN/329.609
| Open Clusters as Galactic Disk Tracers. I. Project Motivation, Cluster Membership, and Bulk Three-Dimensional Kinematics
We have begun a survey of the chemical and dynamical properties of theMilky Way disk as traced by open star clusters. In this firstcontribution, the general goals of our survey are outlined and thestrengths and limitations of using star clusters as a Galactic disktracer sample are discussed. We also present medium-resolution (R ~ 15,0000) spectroscopy of open cluster stars obtained with the Hydramulti-object spectrographs on the Cerro Tololo Inter-AmericanObservatory 4 m and WIYN 3.5 m telescopes. Here we use these data todetermine the radial velocities of 3436 stars in the fields of openclusters within about 3 kpc, with specific attention to stars havingproper motions in the Tycho-2 catalog. Additional radial velocitymembers (without Tycho-2 proper motions) that can be used for futurestudies of these clusters were also identified. The radial velocities,proper motions, and the angular distance of the stars from clustercenter are used to derive cluster membership probabilities for stars ineach cluster field using a non-parametric approach, and the clustermembers so identified are used, in turn, to derive the reliable bulkthree-dimensional motion for 66 of 71 targeted open clusters. Thehigh-probability cluster members that we identify help to clarify thecolor-magnitude sequences for many of the clusters, and are primetargets for future echelle resolution spectroscopy as well asastrometric study with the Space Interferometry Mission (SIMPlanetquest).
| Red giants in open clusters. XIV. Mean radial velocities for 1309 stars and 166 open clusters
Context: Radial velocities have proved to be an efficient method formembership determination if there are at least 2 or 3 red giants in acluster. They are necessary for galactic studies, but are still missingfor many open clusters. Aims: We present the final catalogues of along-term observing programme performed with the two coravelspectrovelocimeters for red giants in open clusters. The main aims wereto detect spectroscopic binaries and determine their orbital parameters,determine the membership, and compute mean velocities for the stars andopen clusters. Methods: We computed weighted mean radial velocities for1309 stars from 10 517 individual observations, including the systemicradial velocities from spectroscopic orbits and for cepheids. Results:The final results are contained in three catalogues collecting 10 517individual radial velocities, mean radial velocities for 1309 redgiants, and mean radial velocities for 166 open clusters among whichthere are 57 new determinations. We identified 891 members and 418non-members. We discovered a total of 288 spectroscopic binaries, amongwhich 57 are classified as non-members. In addition 27 stars were judgedto be variable in radial velocities and they are all red supergiants. Conclusions: The present material, combined with recent absolute propermotions, will permit various investigation of the galactic distributionand space motions of a large sample of open clusters. However, thedistance estimates still remain the weakest part of the necessary data.This paper is the last one in this series devoted to the study of redgiants in open clusters based on radial velocities obtained with thecoravel instruments.Based on observations collected at the Haute-Provence Observatory(France) and on observations collected with the Danish 1.54-m telescopesat the European Southern Observatory, La Silla, Chile. Full Tables [seefull textsee full textsee full textsee full textsee full text] to [seefull textsee full textsee full textsee full textsee full text] are onlyavailable and Tables [see full textsee full textsee full textsee fulltextsee full text] and [see full textsee full textsee full textsee fulltextsee full text] are also 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/485/303
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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
| Red giants in open clusters. III - Binarity and stellar evolution in five intermediate-age clusters: NGC 2360, 2423, 5822, 6811, and IC 4756
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990A&A...237...61M&db_key=AST
| Photometric metal abundances of high-luminosity red stars in young and intermediate-age open clusters
UBV, DDO, and Washinton photometry has been obtained for G and K starslocated in or near 22 young and intermediate-age open clusters. Nearly65 percent of the observed stars are found to have a high probability ofbeing cluster members, while the remaining 35 percent are likely to bered field stars. Five clusters (NGC 2383, NGC 3033, Ruprecht 20, NGC5168, and NGC 6249) probably do not contain any red giants. Sixteenclusters are found to be nearly solar in composition; three are slightlymetal-poor or metal-rich; one (Ruprecht 20) is moderately metal-poor(Fe/H = -0.3); and another (NGC 5617) is moderately metal-rich (Fe/H =0.3). None of the clusters with derived Washington abundances appear tobe enriched in elements of the CNO group.
| Yellow evolved stars in open clusters
This paper describes a program in which Galactic cluster post-AGBcandidates were first identified and then analyzed for clustermembership via radial velocities, monitored for possible photometricvariations, examined for evidence of mass loss, and classified ascompletely as possible in terms of their basic stellar parameters. Theintrinsically brightest supergiants are found in the youngest clusters.With increasing cluster age, the absolute luminosities attained by thesupergiants decline. It appears that the evolutionary tracks ofluminosity class II stars are more similar to those of class I than ofclass III. Only two superluminous giant star candidates are found inopen clusters.
| Intermediated-band photometry of late-type stars. IX - Two Hyades-like clusters
Observations of NGC 2423 and 2482 are discussed. NGC 2423 has a dozenearly G-type to late K-type giants. Although the reddest and brightestgiant needs confirmation of cluster membership, the remaining stars showa color-luminosity distribution very similar to that found previouslyfor the Hyades group giants, and a chemical homogeneity with the Hyadesgroup giants. A preliminary (Mv, C1)-calibration is briefly discussed.NGC 2482, which may contain the cataclysmic variable BX Pup, is slightlyyounger than the Hyades and NGC 2323, but the metal abundance issimilar.
| Three-colour photometry of southern galactic clusters I,
Not Available
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Observation and Astrometry data
| Constellation: | とも座 |
| Right ascension: | 07h36m59.00s |
| Declination: | -13°54'56.0" |
| Apparent magnitude: | 9.783 |
| Proper motion RA: | -0.1 |
| Proper motion Dec: | -4.8 |
| B-T magnitude: | 11.251 |
| V-T magnitude: | 9.905 |
Catalogs and designations:
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INHABITED SKY
