Cyclotron spectroscopy of VV Puppis

Abstract

We present phase-resolved spectrophotometric observations of VV Puppis obtained during two different states of accretion. We confirm the detection of cyclotron lines from emission regions at both poles (Wickramasinghe et al. 1989) having significantly different field strength of B1 ≃ 31 MG and B2 ≃ 54 MG. Our phase-resolved data allowed the detection of phase-dependent wavelength shifts of the cyclotron lines from the main accretion pole which is due to the varying aspect of the observer. A corresponding motion of the cyclotron lines from the secondary pole appears likely. Compared to 1984, the cyclotron lines from the main pole appeared redshifted in 1989, during an episode of higher system brightness. This shift can be explained assuming either different locations of the accretion spot and, hence, variations of the magnetic field, or variations of the plasma temperature both triggered by variations of the mass accretion rate. The cyclotron lines from the second pole do not show such changes suggesting that the coupling region for the weakly accreting pole is more or less stationary whereas the coupling region of the main pole varies in space, most likely depending on the mass accretion rate.Key words: cataclysmic variables -AM Herculis binaries -stars: individual (VV Pup) -cyclotron radiation -stars: magnetic field AAA subject classification: 119; 120; 122 IntroductionVV Puppis was recognized as third AM Herculis binary by the detection of strong and periodic variable linear and circular polarization by Tapia (1977). A high orbital inclination of i ∼ 75• and a high "southern" colatitude of the main accretion region of δ ∼ 150• lead to a long selfeclipse of this main spot by the white dwarf itself as the system rotates. Visvanathan and Wickramasinghe (1979) and Stockman et al. (1979, hereafter SLB) detected intense low-frequency modulations of the continuum spectra during the bright phase, with the minima originally explained as cyclotron absorption troughs in a field of ∼ 30 MG. Later, when detailed cyclotron models became available, the maxima in intensity were interpreted as cyclotron line emission and the field strength was redetermined to 31.5 -32.0 MG (Wickramasinghe & Meggitt 1982;Barrett & Chanmugam 1985).Photometric variations and nonvanishing circular polarization during the faint phase, when the main accreting pole is out of view, have been interpreted by Liebert and Stockman (1979) as due to accretion in the vicinity of the second pole. Wickramasinghe et al. (1989, hereafter WFB) confirmed this supposition by the detection of two independent systems of cyclotron lines originating from both accretion regions. The field strength in the secondary region was found to be surprisingly high, B 2 ≃ 56 MG, and the newly determined field strength for the primary pole, B 1 = 30.5 MG, was lower than during the initial observations. These findings have been interpreted assuming that accretion occurs at the footpoint of the same closed field line in a decentered dipole field (d off ≃ 0.1R wd ). The lower value o...

Cyclotron spectroscopy of HU Aquarii

“…Cyclotron harmonic motion was recognized earlier in V834 Cen , UZ For ), MR Ser (Wickramasinghe et al 1991, and in VV Pup (Schwope & Beuermann 1997). In all these cases the motion of cyclotron harmonic humps was explained as being the result of a different aspect angle of the accreting field line in the hot accretion spot while the white dwarf rotates.…”

First detection of Zeeman absorption lines in the polar VV Puppis

“…In the past VV Pup has been observed to accrete through both the magnetic poles (e.g. Visvanathan & Wickramasinghe 1981;Wickramasinghe et al 1989;Schwope & Beuermann 1997), as well as just the main one (e.g. Wickramasinghe & Visvanathan 1980;Canalle & Opher 1988;Wickramasinghe et al 1984), during high states.…”

“…Previous investigators have noted phase shifts between the relative positions of the accretion shocks at different states of activity and have used cyclotron spectroscopy also to argue against the closed field line assumption (e.g. Schwope & Beuermann 1997).…”

Cyclotron Modeling Phase‐Resolved Infrared Spectroscopy of Polars. II. EQ Ceti, AN Ursa Majoris, and VV Puppis

“…(1996) ephemeris, and a flux increment of 5:0 ; 10 À12 ergs s À1 cm À2 is added to each spectrum. Schwope & Beuermann (1997) determined the following system parameters for VV Pup. The primary pole was found to be at high southern colatitude, 1 ¼ 145 Y155 , whereas the secondary pole is near the north pole, 2 ¼ 10 , with a significant separation in azimuth between the two accretion regions, ÁÉ 12 ¼ 165 .…”