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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.
| Deep near-infrared spectroscopy of submillimetre-selected galaxies
We present the results of deep near-infrared spectroscopy of sevensubmillimetre-selected galaxies from the Submillimetre Common UserBolometer Array (SCUBA) 8-mJy Survey and Canada-UK Deep SubmillimetreSurvey (CUDSS). These galaxies were selected because they are too faintto be accessible to optical spectrographs on large telescopes. We obtaina spectroscopic redshift for one object, and likely redshifts for twomore, based on a combination of marginal emission-line detections andthe shape of the continuum. All three redshifts broadly agree withestimates from their radio/submm spectral energy distributions. From theemission-line strengths of these objects, we infer star formation ratesof 10-25 Msolar yr-1, while the lack of detectionsin the other objects imply even lower rates. By comparing our resultswith those of other authors, we conclude it is likely that the vastmajority (more than 90 per cent) of the star formation in these objectsis completely extinguished at rest-frame optical wavelengths, and theemission lines originate in a relatively unobscured region. Finally, welook at future prospects for making spectroscopic redshiftdeterminations of submm galaxies.
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