اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدPhotometric constraints on white dwarfs and the identification of extreme objects
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It is possible to reliably identify white dwarfs (WDs) without recourse to spectra, instead using photometric and astrometric measurements to distinguish them from Main Sequence stars and quasars. WDs colours can also be used to infer their intrinsic properties (effective temperature, surface gravity, etc.), but the results obtained must be interpreted with care. The difficulties stem from the existence of a solid angle degeneracy, as revealed by a full exploration of the likelihood, although this can be masked if a simple best-fit approach is used. Conversely, this degeneracy can be broken if a Bayesian approach is adopted, as it is then possible to utilise the prior information on the surface gravities of WDs implied by spectroscopic fitting. The benefits of such an approach are particularly strong when applied to outliers, such as the candidate halo and ultra-cool WDs identified by Vidrih et al. (2007). A reanalysis of these samples confirms their results for the latter sample but suggests that that most of the halo candidates are thick disk WDs in the tails of the photometric noise distribution.
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The white dwarf luminosity function has proven to be an excellent tool to study some properties of the galactic disk such as its age and the past history of the local star formation rate. The existence of an observational luminosity function for halo
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