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Distribution and Space Density of Soft X-ray Emitting Polars in the Solar Neighbourhood

Published online by Cambridge University Press:  12 April 2016

H.-C. Thomas  and
K. Beuermann
H.-C. Thomas
Affiliation:
Max–Planck–Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85740 Garching, Germany
K. Beuermann
Affiliation:
Universitäts-Sternwarte, Geismarlandstr. 11, D-37083 Göttingen, Germany Max–Planck–Institut für extraterrestrische Physik, Giessenbachstrasse, D-85740 Garching, Germany

Extract

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The ROSAT All Sky Survey (RASS) was the first one performed with an imaging telescope in the soft X-ray regime and has led to the discovery of numerous new objects whose emission is dominated by soft X-rays. Among these are white dwarfs and a subclass of the cataclysmic variables (CVs), the Polars or AM Herculis binaries. From a pre-ROSAT census of only 17, the number of known sources of this class has increased to some 55 (Beuermann and Thomas 1993, Beuermann 1997). Distances or lower limits to the distance are available for some 35 of these, based on the detection or non-detection of the TiO-Features in their optical red spectra. The derived distances range from below 100 pc up to ~ 600 pc, implying that many of these objects are located within the “Local Bubble” of low gas density in interstellar space. As the soft X-ray emission can be reasonably well represented by blackbody emission with a typical temperature of kT bb ≃ 25 eV, spectral fits to the ROSAT PSPC spectra from either the All-Sky-Survey (RASS) or from subsequent pointed ROSAT observations allow to determine the foreground absorption column density in the direction of the polars.

Type
Part V Magnetic Fields, Molecular Clouds, and Interstellar Bubbles
Information
International Astronomical Union Colloquium , Volume 166: The Local Bubble and Beyond , 1997 , pp. 247 - 250
Copyright
Copyright © Springer-Verlag 1998

References

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