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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.
| 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
| The Maximum Age of Trapezium Systems
We sought to determine the maximum age of Trapezium systems by studyingpossible trapezium systems that were selected independently of theiroccurrence in H II regions. We started with the unpublished catalog byAllen, Tapia, & Parrao of all the known visual systems having threeor more stars in which the maximum separation is less than 3.0 times theminimum separation. Their catalog has 968 such systems whose mostfrequent primary type is F, which does not describe young systems. Witha CCD on the Kitt Peak 0.9 m telescope we obtained UBV frames for 265systems accessible with our equipment on Kitt Peak. The frames were usedto obtain UBV photometry for about 1500 stars with an accuracy of+/-0.04 mag between V=7 and 14 mag. Also these frames were used toobtain astrometry with an accuracy of +/-0.015d in position angle and+/-0.01" in separation. For the brightest star in each system weobtained a spectral type to determine the distance and reddening to thesystem. The measures were used to determine physical membership fromstars that (1) fit a single color-magnitude diagram, (2) fit a commoncolor-color diagram, and (3) show no astrometric motion compared tovisual measures made (mostly) a century ago. Combining the results withspectroscopic data for 20 additional Allen et al. systems by Abt, wefound that 126 systems had only optical companions to the primaries, 116systems contained only a single physical pair, 13 were hierarchicalsystems with 3-6 members and having separation ratios of more than afactor of 10, two were small clusters, and only 28 fitted the criteriaof Trapezium systems. However, as shown by Ambartsumian, about 9% of thehierarchical systems should appear to be Trapezium systems inprojection. Those, like other hierarchical systems, have a broaddistribution of primary spectral types. We isolated 14 systems that seemto be true Trapezium systems. They have primary types of B3 or earlier,indicating a maximum age of about 5×107 yr. This upperlimit is consistent with the estimate made by Allen & Poveda for anage of several million years for these dynamically unstable systems.These Trapezia are also large with a median radius of 0.2 pc and amaximum radius of 2.6 pc. We asked why the sample of 285 possibleTrapezium systems yielded only 14 true ones, despite the attempt made byAllen et al. to eliminate optical companions with a ``1% filter,'' i.e.,demanding that each companion have less than a 1% chance of being afield star of that magnitude within a circle of its radius from theprimary. The explanation seems to be that the double star catalogs arebased mostly on BD magnitudes that, fainter than V=12 mag, aresystematically too faint by 1 mag.
| 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. VIII. NGC 752
The results of an 18-year radial-velocity survey of 30 red giants in thefield of the open cluster NGC 752 are presented. The membership of 15stars is confirmed. Four spectroscopic binaries have been discoveredamong the members and three orbits have been determined for H75, 110 and208, with periods of 3321, 127 and 5276 days respectively. The binaryfrequency (27%) is normal. A search for additional members in a widesurrounding area (2degr ) yielded two possible new members: both areclump red giant candidates. The red giant distribution in thecolour-magnitude diagram is somewhat unusual, with a clump containing 8stars and a second, fainter feature extending to the blue, defined by 3or 4 stars, which is not accounted for by theoretical isochrones. Basedon observations collected at the Haute-Provence Observatory (France)
| A photometric and radial-velocity analysis of the intermediate-age open cluster NGC 752
Using all available proper-motion and radial-velocity data, includingnew radial-velocity observations obtained for this investigation,probable members of the open cluster NGC 752 have been identified.Photoelectric data on six systems have been transformed and collated toform an internally consistent sample on the BV system. Binaries havebeen identified using photometric and radial-velocity data, including aphotographic survey for variability and the radial-velocity observationsof this study. Analysis of the data leads to the following clusterparameters and their probable errors: E(B - V) = 0.035 plus or minus0.005 mag, Fe/H = -0.15 plus or minus 0.05 dex, and (m - M) = 8.25 plusor minus 0.10 mag. The spread in color among stars in thecolor-magnitude diagram (cmd) along the main sequence from the turnoffto the unevolved main sequence is the consequence of a rich populationof binaries. Due to its age and the comprehensive data available for thecluster, NGC 752 provides an ideal test of a variety of evolutionaryphenomena. Comparison with theoretical isochrones normalized in aninternally consistent manner leads to the conclusion that the morphologyand distribution of stars in the cmd can best be matched using modelsthat include convective overshoot, particularly those of Schaller et al.(1992, A&AS, 96, 269). Despite their differences, the traditional andthe overshoot isochrones both imply very similar ages, 1.9 plus or minus0.2 Gyr and 1.7 plus or minus 0.1 Gyr, respectively, for the cluster.The Li abundances for the giants confirm that the giant branch isdominated by clump stars and first-ascent giants below the luminosity ofthe clump. The position and size of the Li dip among the main-sequencestars, compared to the Hyades, is readily explained by stellar evolutionwith convective overshoot. It is predicted that among turnoff stars inthe intermediate-age range Li will cease to be a unique function of ageat a given color. Chromospheric flux is shown to be a well-definedfunction of color for single, unevolved stars, identical to that foundfor the Hyades, and the relation for NGC 752 falls within theVaughan-Preston gap. However, the slope of the relation requires thatincreasing color implies increasing age for the bluer portion of theweak-emission boundary. The combined effect of small samples, randomerrors, emission limits, a possible selection bias in favor of turnoffstars, and metallicity corrections is to render highly questionable anyinterpretation of time-variable star formation within the Galaxy basedupon chromospheric ages.
| The studies of proper motions in the regions of open clusters. II - NGC 752
Relative proper motions of 1777 stars in the region of the open clusterNGC 752 have been determined from the PDS measurements of eleven Pulkovonormal astrograph plates. In a 110-arcmin-diameter circle around thecluster, 175 stars have membership probabilities P greater than 0percent. The total number of cluster stars, obtained by weighting themwith membership probabilities, reaches 130. The catalog of propermotions is complete down to m(pg) = 150 mag, the limiting value is 154mag. The average standard error of the catalog proper motions variesfrom + or - 000075 arcsec/yr to + or - 00011 arcsec/yr for the rest. Theluminosity function for cluster stars shows a deficiency of faint stars.
| Lithium in giant stars in NGC 752 and M67
Spectra of giant stars in the intermediate-age galactic cluster NGC 752and in the old cluster M67 were studied for the presence of Li I 6707 A.The lithium feature is not present in any of the M67 giants observed;this may be because these giants evolve from progenitors in the regionof the main-sequence lithium dip. While lithium is not present in mostNGC 752 giants, the feature is strong in Heinemann 77 and 208. Theabundances are log epsilon (Li) = + 1.1 and + 1.4, respectively.
| Vitesses radiales dans la region de l'amas NGC 752.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&A.....4..404R&db_key=AST
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לינקים קשורים
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | אנדרומדה |
| התרוממות ימנית: | 01h54m39.65s |
| סירוב: | +38°11'45.5" |
| גודל גלוי: | 8.887 |
| מרחק: | 173.913 פארסק |
| תנועה נכונה: | 7.3 |
| תנועה נכונה: | -11.7 |
| B-T magnitude: | 10.167 |
| V-T magnitude: | 8.993 |
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