Distribution and Space Density of Soft X-ray Emitting Polars in the Solar Neighbourhood
Abstract
AM Herculis binaries or polars belong to the softest X-ray sources. The majority of the presently known ~55 members of the class was unknown before the ROSAT All-Sky-Survey. X-ray observations combined with optical spectroscopy have yielded information on the hydrogen column densities along the lines of sight and on the distances. Few polars are observed in regions of high interstellar absorption, i.e. the galactic plane and also the North-Polar Spur; the observed polars trace out lines of sight of low interstellar column density out to beyond 500 pc. We report results on the space distribution of polars and on the mean number densities of atomic hydrogen along the lines of sight. Within 45^\circ of the South Galactic pole the count of polars is thought to be largely complete which yields a local space density of n_o ~= 6 x 10^{-7} pc^{-3} and a Gaussian scale height of sigma_g ~= 240 pc.
- Publication:
-
IAU Colloq. 166: The Local Bubble and Beyond
- Pub Date:
- 1998
- DOI:
- 10.1007/BFb0104728
- Bibcode:
- 1998LNP...506..247T