Polars
Multisite emission - multiwavelength observation

Invited Review given at the 13th North American Workshop on CVs, Jackson Lake Lodge, Wyoming, June 15-19, 1997
ASP. Conf. Ser. in press (submitted Aug 21, 1997)

Contact: aschwope@aip.de

Preprint of paper (460 kb gzip'ed postscript)

Axel D. Schwope [1], K. Beuermann [2], D.A.H. Buckley [3], D. Ciardi [4], M. Cropper [5], K. Horne [6], S. Howell [4], K.-H. Mantel [7], A. Metzner [1], K. O'Brien [6] R. Schwarz [1], M. Sirk [8], D. Steeghs [6], M. Still [6], H.-C. Thomas [9] (added Aug 21, 1997)

  1. Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
  2. Universitäts-Sternwarte Göttingen, Geismarlandstr. 11, 37083 Göttingen, Germany
  3. South African Astronomical Observatory, PO Box 9, Observatory 7935, Cape Town, RSA
  4. Department of Physics and Astronomy, University of Wyoming, P.O. Box 3905, University Station, Laramie, WY, 82071, USA
  5. MSSL, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
  6. Univ. of St. Andrews, School of Physics and Astronomy, North Haugh, St. Andrews, Fife KY16 9SS, Scotland, UK
  7. Universitätssternwarte München, Scheinerstrasse 1, 81679 München, Germany
  8. Center for EUV Astrophysics, University of California, Berkeley CA 94720, USA
  9. MPI für Astrophysik, Karl-Schwarzschild-Str. 1, 85740 Garching, Germany

Abstract

We review the main observational characteristics of AM Herculis stars (polars) at X-ray, EUV, UV, IR and optical wavelengths. Particular emphasis is given to multi-epoch, multi-wavelength observations of the eclipsing polar HU Aqr (RX J2107.9-0518).
In AM Herculis stars the broad-band spectral energy distribution from X-rays to the IR is governed by only very small structures: the hot accretion regions on the footpoints af accreting field lines. The most extended structures in the binary systems on the other hand, the mass-donating secondary stars and the accretion streams, distinctly appear only as Doppler-shifted emission or absorption lines. They can best be studied by investigating selected narrow spectral features in the optical, ultraviolet or the near infrared.
In this contribution both aspects will be highlighted, the structure of the accretion regions as inferred from multi-wavelength observations with low or no spectral resolution, as well as the structure of the secondary stars and the accretion streams as inferred from high-resolution spectral observations and Doppler mapping.

Key words: Accretion - cataclysmic variables - AM Herculis binaries - X-rays