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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.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| Metal Abundances and Kinematics of Bright Metal-poor Giants Selected from the LSE Survey: Implications for the Metal-weak Thick Disk
We report medium-resolution (1-2 Å) spectroscopy and broadband(UBV) photometry for a sample of 39 bright stars (the majority of whichare likely to be giants) selected as metal-deficient candidates from anobjective-prism survey concentrating on Galactic latitudes below|b|=30°, the Luminous Stars Extension (LSE) survey of Drilling &Bergeron. Although the primary purpose of the LSE survey was to selectOB stars (hence the concentration on low latitudes), the small number ofbright metal-deficient giant candidates noted during this survey provideinteresting information on the metal-weak thick disk (MWTD) population.Metal abundance estimates are obtained from several different techniquesand calibrations, including some that make use of the availablephotometry and spectroscopy and others that use only the spectroscopy;these methods produce abundance estimates that are consistent with oneanother and should be secure. All of the targets in our study haveavailable high-quality proper motions from the Hipparcos or Tycho IIcatalogs, or both, that we combine with radial velocities from ourspectroscopy to obtain full space motions for the entire sample. Therotational (Vφ) velocities of the LSE giants indicatethe presence of a rapidly rotating population, even at quite lowmetallicity. We consider the distribution of orbital eccentricity of theLSE giants as a function of [Fe/H] and conclude that the local fraction(i.e., within 1 kpc from the Sun) of metal-poor stars that might beassociated with the MWTD is on the order of 30%-40% at abundances below[Fe/H]=-1.0. Contrary to recent analyses of previous (much larger)samples of nonkinematically selected metal-poor stars (assembledprimarily from prism surveys that concentrated on latitudes above|b|=30°), we find that this relatively high fraction of localmetal-poor stars associated with the MWTD may extend to metallicitiesbelow [Fe/H]=-1.6, much lower than had been considered before. Weidentify a subsample of 11 LSE stars that are very likely to be membersof the MWTD, based on their derived kinematics; the lowest metallicityamong these stars is [Fe/H]=-2.35. Implications of these results for theorigin of the MWTD and for the formation of the Galaxy are considered.
| An Extension of the Case-Hamburg OB Star Surveys
We have extended the Case-Hamburg OB star surveys to b = +- 30 degreesfor l = +- 60 degres using the Curtis Schmidt telescope and 4 degreeobjective prism at the Cerro Tololo Inter-American Observatory. Acatalog of 234 OB stars and other objects with peculiar spectra ispresented along with finding charts for those objects too faint to beincluded on the BD or CD charts. (SECTION: Stars)
| A southern objective prism survey.
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