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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.
| Orbital and physical parameters of eclipsing binaries from the All-Sky Automated Survey catalogue - I. A sample of systems with components' masses between 1 and 2 Msolar
We derive the absolute physical and orbital parameters for a sample of18 detached eclipsing binaries from the All-Sky Automated Survey (ASAS)data base based on the available photometry and our own radial velocity(RV) measurements. The RVs are computed using spectra we collected withthe 3.9-m Anglo-Australian Telescope (AAT) and its University CollegeLondon Echelle Spectrograph (UCLES), and the 1.9-m Radcliffe telescopeand its Grating Instrument for Radiation Analysis with a Fibre-FedEchelle (GIRAFFE) at the South African Astronomical Observatory (SAAO).In order to obtain as precise RVs as possible, most of the systems wereobserved with an iodine cell available at the AAT/UCLES and/or analysedusing the two-dimensional cross-correlation technique (TODCOR). The RVswere measured with TODCOR using synthetic template spectra asreferences. However, for two objects we used our own approach to thetomographic disentangling of the binary spectra to provide observedtemplate spectra for the RV measurements and to improve the RV precisioneven more. For one of these binaries, AI Phe, we were able to the obtainan orbital solution with an RV rms of 62 and 24 m s-1 for theprimary and secondary, respectively. For this system, the precision in Msin3 i is 0.08 per cent.For the analysis, we used the photometry available in the ASAS database. We combined the RV and light curves using PHOEBE and JKTEBOP codesto obtain the absolute physical parameters of the systems. Havingprecise RVs, we were able to reach ~0.2 per cent precision (or better)in masses in several cases but in radii, due to the limited precision ofthe ASAS photometry, we were able to reach a precision of only 1 percent in one case and 3-5 per cent in a few more cases. For the majorityof our objects, the orbital and physical analysis is presented for thefirst time.
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Observation and Astrometry data
| Constellation: | Eridanus |
| Right ascension: | 04h20m40.97s |
| Declination: | -01°44'23.4" |
| Apparent magnitude: | 8.652 |
| Distance: | 116.414 parsecs |
| Proper motion RA: | -21.3 |
| Proper motion Dec: | -45 |
| B-T magnitude: | 9.308 |
| V-T magnitude: | 8.707 |
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