Theoretical astrophysics and plasma physics at RPC

Abstract:

We apply the method of Burnett & Binney (2010) for the determination of stellar distances and parameters to the internal catalogue of the Radial Velocity Experiment (Steinmetz et al. 2006). Subsamples of stars that either have Hipparcos parallaxes or belong to well-studied clusters, inspire confidence in the formal errors. Distances to dwarfs cooler than ~6000 K appear to be unbiased, but those to hotter dwarfs tend to be too small by ~10% of the formal errors. Distances to giants tend to be too large by about the same amount. The median distance error in the whole sample of 216,000 stars is 28% and the error distribution is similar for both giants and dwarfs. Roughly half the stars in the RAVE survey are giants. The giant fraction is largest at low latitudes and in directions towards the Galactic Centre. Near the plane the metallicity distribution is remarkably narrow and centred on [M/H]-0.04 dex; with increasing |z| it broadens out and its median moves to [M/H] ~ -0.5. Mean age as a function of distance from the Galactic centre and distance |z| from the Galactic plane shows the anticipated increase in mean age with |z|.

Abstract:

Our knowledge of the Galaxy is being revolutionized by a series of photometric, spectroscopic and astrometric surveys. Already an enormous body of data is available from completed surveys, and data of ever-increasing quality and richness will accrue at least until the end of this decade. To extract science from these surveys, we need a class of models that can give probability density functions in the space of the observables of a survey - we should not attempt to 'invert' the data from the space of observables into the physical space of the Galaxy. Currently just one class of model has the required capability, the so-called 'torus models'. A pilot application of torus models to understand the structure of the Galaxy's thin and thick discs has already produced two significant results: a major revision of our best estimate of the Sun's velocity with respect to the local standard of rest, and a successful prediction of the way in which the vertical velocity dispersion in the disc varies with distance from the Galactic plane. © Indian Academy of Sciences.