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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.
| The measurement of mass loss rates of binary systems enveloped in winds or expanding shells.
Not Available
| IUE and stars with composite spectra
The IUE contribution to the study of binary stars is reviewed. The valueof ultraviolet spectra in defining the parameters of hot companions indouble systems is emphasized, as this is important for understanding ofthe masses, luminosities, and evolutionary states of both the componentstars. Cataclysmic variables; precataclysmics; symbiotic stars;atmospheric eclipsing binaries; Algols; cool and hot binaries; heavymetal stars; noninteractors; and Cepheids are discussed.
| Mass loss rates in the Hertzsprung-Russell diagram
Mass loss rates have been collected for 271 stars of spectral type Othrough M, primarily of population I. Good agreement is found forresults obtained according to six different methods, and it is shownthat the mass loss rate data can be well represented by one empiricalinterpolation formula as a function of the effective temperature andluminosity. The chemically evolved stars are shown to have mass lossrates which are larger than those of normal stars occupying the samepositions in the Hertzprung-Russell diagram by factors of 160 forWolf-Rayet stars and 11 for C-type stars.
| Some interesting massive spectroscopic binary systems.
Abstract image available at:http://adsabs.harvard.edu/abs/1968AJ.....73..551B
| A Spectroscopic Study of the Peculiar Binary Boss 1985.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1965ApJ...142..299C&db_key=AST
| Long-Term Variations in the Spectrum of Boss 1985.
Not Available
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Osservazione e dati astrometrici
| Costellazione: | Triangolo |
| Ascensione retta: | 01h39m00.06s |
| Declinazione: | +32°06'34.2" |
| Magnitudine apparente: | 9.4 |
| Moto proprio RA: | 16.1 |
| Moto proprio Dec: | -9.5 |
| B-T magnitude: | 10.782 |
| V-T magnitude: | 9.515 |
Cataloghi e designazioni:
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