New low accretion rate magnetic binary systems and their significance for the evolution of cataclysmic variables

Gary D. Schmidt, Paula Szkody, Karen M. Vanlandingham, Scott F. Anderson, J. C. Barentine, Howard J. Brewington, Patrick B. Hall, Michael Harvanek, S. J. Kleinman, Jurek Krzesinski, Dan Long, Bruce Margon, Eric H. Neilsen, Peter R. Newman, Atsuko Nitta, Donald P. Schneider, Stephanie A. Snedden

Research output: Contribution to journalReview articlepeer-review

78 Scopus citations


Discoveries of two new white dwarf plus M star binaries with striking optical cyclotron emission features from the Sloan Digital Sky Survey (SDSS) brings to six the total number of X-ray-faint, magnetic accretion binaries that accrete at rates Ṁ ≲ 10-13 M yr -1, or < 1% of the values normally encountered in cataclysmic variables. This fact, coupled with donor stars that underfill their Roche lobes and very cool white dwarfs, brand the binaries as post-common-envelope systems whose orbits have not yet decayed to the point of Roche lobe contact. They are premagnetic cataclysmic variables, or pre-Polars. The systems exhibit spin-orbit synchronism and apparently accrete by efficient capture of the stellar wind from the secondary star, a process that has been dubbed a "magnetic siphon." Because of this, period evolution of the binaries will occur solely by gravitational radiation, which is very slow for periods >3 hr. Optical surveys for the cyclotron harmonics appear to be the only means of discovery, so the space density of pre-Polars could rival that of Polars, and the binaries provide an important channel of progenitors (in addition to the asynchronous intermediate Polars). Both physical and SDSS observational selection effects are identified that may help to explain the clumping of all six systems in a narrow range of magnetic field strength around 60 MG.

Original languageEnglish (US)
Pages (from-to)1037-1053
Number of pages17
JournalAstrophysical Journal
Issue number2 I
StatePublished - Sep 10 2005

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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