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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.
| Proper motions and CCD photometry of stars in the region of the open cluster NGC 6866
We present the results of our comprehensive study of the Galactic openstar cluster NGC 6866. The positions of stars in the investigated regionhave been obtained with the “Fantasy” automatic measuringmachine from 10 plates of the normal astrograph at the PulkovoAstronomical Observatory. The size of the investigated field is 40'× 40', the limiting magnitude is B ˜16{·/ m }6, and the maximum epochdifference is 79 yr. For 1202 field stars, we have determined therelative proper motions with an rms error of 2.5 masyr-1. Out of them, 423 stars may be considered clustermembers with a probability P > 70% according to the astrometriccriterion. Photometric diagrams have been used as an additionalcriterion. We have performed two-color BV CCD photometry of stars withthe Pulkovo ZA-320M mirror astrograph. The U magnitudes from theliterature have also been used to construct the two-color diagrams. Atotal of 267 stars have turned out to be members of NGC 6866 accordingto the two criteria. We present refined physical parameters of thecluster and its age estimate (5.6 × 108 yr). Thecluster membership of red and blue giants, variable, double, andmultiple stars is considered. We have found an almost completecoincidence of the positions of one of the stars in the region (acluster nonmember) and a soft X-ray source in the ROSAT catalog. The“Fantasy” automatic measuring machine is described in theAppendix.
| Photometric Study of Variable Stars in the Open Cluster NGC 6866
We report the discovery of 19 variable stars and two blue stragglers inthe field of the open cluster NGC 6866. Three of the variable stars weclassify as ? Sct, two as ? Dor, four as W UMa, two asellipsoidal variables, and one as an eclipsing binary. Seven stars showirregular variability. Two of the pulsators, ? Sct star NGC6866-29 and ? Dor star NGC 6866-21, are multiperiodic.From an analysis of proper motions, we conclude that the ? Sctstars, one of the ? Dor stars and both blue stragglers are veryprobable members of the cluster. The position on the color-magnitudediagram of seven other variables suggests that they also belong to thecluster. The eclipsing binary, which we discover to be a new highvelocity star, and the seven irregular variables are non-members.We discuss in detail the age and metallicity of open clusters that host? Dor stars and we show that none of these parameters iscorrelated with the number of ? Dor stars in cluster.
| Spectroscopic Study of Candidates for Kepler Asteroseismic Targets - Solar-Like Stars
We report spectroscopic observations of 23 candidates for Keplerasteroseismic targets and 10 other stars in the Kepler field. For allthese stars, we derive the radial velocities, effective temperature,surface gravity, metallicity, the projected rotational velocity, andestimate the MK type. HIP 97513 and HIP 92132 are classified assuspected new single-lined spectroscopic binaries. For 28 stars, theradial velocity is measured for the first time.
| 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
| The Fiber Multi-Object Spectrograph for the Okayama 188cm Telescope - Development and Observation -
A fiber multi-object spectrograph for the Okayama 188cm telescope (OFMS)has been developed. We found two problems at the observation in 1993.The first was that the spectra were low quality without sufficientphoton counts due to smaller efficiency than expected. The second wasthe complicated procedure in operating the OFMS. We have solved theseproblems with the development started in 1993. Currently, the OFMS iscapable of observing 30 celestial objects simultaneously in a field ofview of 1 degree. The resolution of the spectrograph is?/??=100-150. It is possible to observe spectra ofS/N=100 for a mv=10 star at a 1.25 minutes exposure. In April and May1999, we observed four open clusters and determined the metallicity[Fe/H] for each. We recorded four metallicities as; +0.15 dex forNGC6709, +0.09 dex for IC4665, -0.36 dex for NGC6866, and +0.07dex forNGC6633.
| 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
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Member of following groups:
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Observation and Astrometry data
| Constellation: | Cygnus |
| Right ascension: | 20h03m55.15s |
| Declination: | +44°08'24.2" |
| Apparent magnitude: | 11.763 |
| Proper motion RA: | -6.7 |
| Proper motion Dec: | -3.5 |
| B-T magnitude: | 13.513 |
| V-T magnitude: | 11.908 |
Catalogs and designations:
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