V405 Aurigae: A High Magnetic Field Intermediate Polar

Our simultaneous multicolor (UBVRI) circular polarimetry has revealed nearly sinusoidal variation over the WD spin cycle, and almost symmetric positive and negative polarization excursions. Maximum amplitudes are observed in the B and V bands (±3%). This is the first time that polarization peaking in the blue has been discovered in an intermediate polar (IP), and suggests that V405 Aur is the highest magnetic field IP found so far. The polarized flux spectrum is similar to those found in polars with magnetic fields in the range B ~ 25-50 MG. Our low-resolution circular spectropolarimetry has given evidence of transient features which can be fitted by cyclotron harmonics n = 6, 7, and 8, at a field of B = 31.5 ± 0.8 MG, consistent with the broadband polarized flux spectrum. Timings of the circular polarization zero crossovers put strict upper limits on WD spin period changes, and indicate that the WD in V405 Aur is currently accreting closely at the spin equilibrium rate, with very long synchronization timescales, Ts > 109 yr. For the observed spin to orbital period ratio, Pspin/Porb = 0.0365, and Porb ~ 4.15 hr, existing numerical accretion models predict spin equilibrium condition with B ~ 30 MG if the mass ratio of the binary components is q1 ~ 0.4. The high magnetic field makes V405 Aur a likely candidate as a progenitor of a polar.

[1]  P. A. EvansCoel Hellier Why does the intermediate polar V405 Aurigae show a double-peaked spin pulse? , 2004 .

[2]  Paul S. Smith,et al.  AR Ursae Majoris: The First High-Field Magnetic Cataclysmic Variable , 1996 .

[3]  B. Warner Cataclysmic Variable Stars by Brian Warner , 1995 .

[4]  Keith O. Mason,et al.  Optical and X-ray observations of AO Piscium and the origin of the spin pulse in intermediate polars , 1991 .

[5]  J. Bailey,et al.  Detection of photospheric Zeeman features and cyclotron emission lines in V834 CEN in a low state , 1992 .

[6]  Keith O. Mason,et al.  EXOSAT X-ray observations of the eclipsing magnetic cataclysmic variable EX Hya. , 1988 .

[7]  G. Berriman,et al.  The discovery of near-infrared polarized cyclotron emission in the intermediate polar BG Canis Minoris , 1987 .

[8]  A. Norton,et al.  Discovery of polarized emission from the long period intermediate polar RX J2133.7+5107 , 2007 .

[9]  Vilppu Piirola,et al.  Polarimetric Study of the Massive Interacting Binary W Serpentis: Discovery of High-Latitude Scattering Spot/Jet , 2005 .

[10]  A. King,et al.  The accretion curtain model for intermediate polars - I. A kinematical model for radial velocity and velocity dispersion. , 1993 .

[11]  Kinwah Wu,et al.  Intermediate polars as low-field magnetic cataclysmic variables , 1991 .

[12]  M. Still,et al.  Spectroscopic evidence for two-pole accretion in the intermediate polar RX J0558+5353 , 1998 .

[13]  R. Schulte-Ladbeck,et al.  Polarized radiation of circumstellar origin , 1988 .

[14]  A. Norton,et al.  Pulsations and orbital modulation of the intermediate polar 1WGA J1958.2+3232 , 2002, astro-ph/0201088.

[15]  V. Piirola,et al.  The discovery of variable polarization over the 13.9 minute spin period of the intermediate polar RE 0751+14 , 1993 .

[16]  R. Hilditch,et al.  The spin period of the intermediate polar RX J0558+53. , 1996 .

[17]  Discovery of circular polarization in the Intermediate Polar 1WGA J1958.2+3232 , 2001, astro-ph/0103519.

[18]  D. Wickramasinghe,et al.  The polarization properties of magnetic accretion columns – III. A grid of uniform temperature and shock front models , 1985 .

[19]  K. O. Mason,et al.  Simultaneous UBVRIJK photometric and polarimetric observations of PQ Gem , 1997 .

[20]  A. Schwarzenberg-Czerny,et al.  ROSAT OBSERVATIONS OF RX J1712.6-2414 : A DISCLESS INTERMEDIATE POLAR ? , 1997 .

[21]  M. Cropper,et al.  The magnetic field in four AM HER systems - Measurements from cyclotron humps , 1989 .

[22]  J. Liebert,et al.  Circular polarization in the DQ Herculis binary 3A 0729+103 , 1986 .

[23]  S. R. Rosen,et al.  RE0751 + 14, the first ‘intermediate’ polar? , 1993 .

[24]  A. J. Norton,et al.  The Accretion Flows and Evolution of Magnetic Cataclysmic Variables , 2007, 0709.4186.

[25]  J. Bailey,et al.  1H 1752+08: the lowest field AM Herculis system? , 1995 .

[26]  T. Belloni,et al.  BeppoSAX observations of soft X-ray intermediate polars , 2004 .

[27]  Keith O. Mason,et al.  Spin-down in PQ Gem , 1997 .

[28]  A. J. Norton,et al.  The Spin Periods and Magnetic Moments of White Dwarfs in Magnetic Cataclysmic Variables , 2004, astro-ph/0406363.

[29]  The emission‐line pulse pattern in the intermediate polar RX J0558+53 , 1999, astro-ph/9903461.