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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.
| On the infrared void in the Lupus dark clouds
Strömgren uvbyβ photometry observations obtained for 205 starsin the general direction of a void in the IRAS 100-μm emission fromthe Lupus dark cloud complex are presented and analysed. The colourexcess versus distance diagram confirms the existence of a regiondepleted from interstellar material, which is also seen in the ROSATsoft X-ray background emission map. The distance to the surroundingmaterial is estimated as being within the interval from 60 to 100pc.This result is in disagreement with previous distance estimates to thesupposed supernova that has been suggested as responsible for clearingthe region from dust. As an alternative, the data presented support thesuggestion that the void may have been produced by the detachment ofmaterial from the interface between LoopI and the Local Bubble as aconsequence of hydromagnetic instabilities. Moreover, the distributionof colour excess as a function of distance supports a value of ~150pc asthe most probable distance to the dark cloud known as Lupus1.
| SANTIAGO 91, a right ascension catalogue of 3387 stars (equinox J2000).
The positions in right ascension of 3387 stars belonging to the Santiago67 Catalogue, observed with the Repsold Meridian Circle at Cerro Calan,National Astronomical Observatory, during the period 1989 to 1994, aregiven. The average mean square error of a position, for the wholeCatalogue, is +/-0.009 s. The mean epoch of the catalogue is 1991.84.
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| Сазвежђа: | Вук |
| Ректацензија: | 15h40m11.47s |
| Deклинација: | -30°44'06.9" |
| Apparent магнитуда: | 9.212 |
| Proper motion RA: | -26.7 |
| Proper motion Dec: | -13.2 |
| B-T magnitude: | 9.722 |
| V-T magnitude: | 9.255 |
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