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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.
| Seven-Color Vilnius Photometry of the Open Cluster NGC 752
New photoelectric seven-color observations in the Vilnius system arepresented for 65 stars in the region of the open cluster NGC 752. Basedon individual stars with accurate photometric classifications, wedetermine the apparent distance modulus (m-M)V = 8.38±0.14 and the mean reddening to the cluster EY-V=0.027± 0.010, or EB-V= 0.034± 0.013 (the errorsgiven are the standard deviations for one star). The mean photometricmetallicity for the main-sequence stars, [Fe/H] = -0.14± 0.03, isfound to be slightly lower than that derived for the red clump giants,[Fe/H] = -0.08± 0.09. This difference suggests that red giants inlater evolutionary phases may not have zero-age surface values of[Fe/H]. We made use of the least-squares minimization techniques to fitthe Padova theoretical isochrones to the CMD, when the binary starpopulation is taken into account. By varying the distance modulus,metallicity and age, the best match has been found between the sevenmagnitudes and colors of the observed stars and those of model binaries,which gives the distance modulus by 0.2 mag smaller than that derivedfrom individual stars, i.e., (m-M)V = 8.18, a closely similarmetallicity ([Fe/H] = -0.12), and age of 1.6 Gyr. With these results,the fraction of photometric binaries among the main-sequence stars is≥40%.
| Extended Strömgren Photoelectric Photometry in NGC 752
Photoelectric photometry on the extended Strömgren system (uvbyCa)is presented for 7 giants and 21 main-sequence stars in the old opencluster NGC 752. Analysis of the hk data for the turnoff stars yields anew determination of the cluster mean metallicity. From 10 single-starmembers, [Fe/H]=-0.06+/-0.03, where the error quoted is the standarderror of the mean and the Hyades abundance is set at [Fe/H]=+0.12. Thisresult is unchanged if all 20 stars within the limits of the hkmetallicity calibration are included. The derived [Fe/H] is in excellentagreement with past estimates, using properly zeroed m1 data,transformed moderate-dispersion spectroscopy, and recent high-dispersionspectroscopy.
| 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
| 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.
| Multicolour photoelectric photometry of the open cluster NGC 752
In the open cluster NGC 752, 89 stars are observed in the Vilniusseven-color photometric system, including probable members fainter thanobserved hitherto. Spectral classification of observed stars are madeand individual reddening values are determined. The mean reddening ofthe cluster stars is equivalent E(B - V) = 0.025 m. By fitting on colorindex-magnitude diagrams the cluster Main Sequence with the Hyades onethe distance modulus (m - M)0 = 8.15 +/- 0.15 m is found. For 11 redgiant members of the cluster absolute magnitudes are derived andcompared with ones of the standard calibration. It is obtained that thecluster giants are on average 0.6 m fainter than giants of thecorresponding spectral class in the solar vicinity.
| 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.
| Positions and Magnitudes in the Area of the Open Cluster NGC752
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985RMxAA..11..103S&db_key=AST
| Some Characteristics of the Moderately Old Open Cluster NGC 752
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972ApJ...177..653G&db_key=AST
| Four-color and H-beta photometry of open clusters - V - NGC 752.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75..946C&db_key=AST
| 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
| Photometry of the galactic cluster NGC 752
Not Available
| The Spectrum-Luminosity Diagram for NGC 752.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1955ApJ...121..454R&db_key=AST
| Proper Motions in the Galactic Cluster NGC 752.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1939ApJ....89..431E&db_key=AST
| Photometrische Vermessung der Sternhaufen NGC 752 und IC 4665
Not Available
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