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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.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
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| Interstellar polarization at high galactic latitudes from distant stars. 2: First results for Z less than or equal to 600 PC
We present the first results from our Crimean-Tuorla program forpolarimetry of distant stars at high galactic latitudes. The availableobservations reveal a clear increase in the interstellar linearpolarization of A and F stars, up to Z approximately equals 600 pc whereone reaches PV approximately equals 0.25%. This means anaverage AB greater than or equal to 0.11 mag over thenorthern polar cap for the diffuse component of the interstellarextinction that we are probing. There is no clear indication in the datathat the asymptotic level of PV has been reached, and withfuture observations above Z = 600 pc we shall investigate this question.The trend found is in agreement with the stellar reddening analysis byTeerikorpi (1990). The directions of the plane of vibration are inagreement with Markkanen's (1979) analysis of closer (Z less than 200pc) stars in his 'Area II'. Outside of this area we define two sectors Band C which encompass the Local Spiral Arm and had little stars inprevious investigations. Here the polarization vectors deviate stronglyfrom those in Markkanen's Area II, where one is probably looking at aninterarm region, close to the edge of the Local Spiral Arm. Ourmeasurements indicate for B and C average polarization vectorsconsistent with the direction l approximately equals 110 deg obtained byother authors for the magnetic field in the Local Spiral Arm using therotation measure method.
| UBVRI photometry of G, K, M HIPPARCOS stars
UBVRI data are presented for a set of 229 late-type stars, most of thembeing high proper motion stars. All these data are part of the InputCatalog planned observations for the Hipparcos mission.
| Further Studies of A-Stars and F-Stars in the Region of the North Galactic Pole - Part Four - a Catalogue of Uvbyr Photometry and Derived Quantities
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| Further Studies of A-Stars and F-Stars in the Region of the North Galactic Pole - Part Three - a Catalogue of Star Names and Positions
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| Studies of A and F stars in the region of the North galactic pole-II. uvby β photometry
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| A finding-list of stars of spectral type F2 and earlier in a north galactic pole region.
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Observation and Astrometry data
| Constellation: | Grande Ourse |
| Right ascension: | 11h50m56.86s |
| Declination: | +29°48'47.0" |
| Apparent magnitude: | 10.13 |
| Proper motion RA: | -41.4 |
| Proper motion Dec: | -0.4 |
| B-T magnitude: | 10.625 |
| V-T magnitude: | 10.171 |
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