TY - JOUR
T1 - New low accretion rate magnetic binary systems and their significance for the evolution of cataclysmic variables
AU - Schmidt, Gary D.
AU - Szkody, Paula
AU - Vanlandingham, Karen M.
AU - Anderson, Scott F.
AU - Barentine, J. C.
AU - Brewington, Howard J.
AU - Hall, Patrick B.
AU - Harvanek, Michael
AU - Kleinman, S. J.
AU - Krzesinski, Jurek
AU - Long, Dan
AU - Margon, Bruce
AU - Neilsen, Eric H.
AU - Newman, Peter R.
AU - Nitta, Atsuko
AU - Schneider, Donald P.
AU - Snedden, Stephanie A.
PY - 2005/9/10
Y1 - 2005/9/10
N2 - 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.
AB - 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.
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U2 - 10.1086/431969
DO - 10.1086/431969
M3 - Review article
AN - SCOPUS:26844544300
SN - 0004-637X
VL - 630
SP - 1037
EP - 1053
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2 I
ER -