Two-pole accretion in the high-field polar RXJ 1938.6-4612. (original) (raw)

NASA/ADS

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Abstract

We report the discovery of two systems of cyclotron emisson lines in phase-resolved low-resolution spectra of the recently discovered AM Herculis binary RXJ 1938.6-4612. The fieldstrengths inferred are B_1_=~47MG and B_2_=~70-80MG, which might be indicative of a non-dipolar field structure. The latter value is the highest found so far for white dwarfs in cataclysmic variables. We present a spectroscopic ephemeris of sufficient accuracy to connect our optical and ROSAT All Sky Survey X-ray observations separated by a few years. Using this, the X-ray bright accretion spot which is visible for less than 40% of the binary cycle may be identified with the low-field accretion region. The high-field spot dominates the optical lightcurve. We find slight evidence for a quadratic term in the ephemeris, ˙(P)=(-3.4+/-2.1)x10^-9^. Low-state spectra reveal M-star features, Zeeman absorption troughs from the white dwarf and cyclotron emission lines originating in the high-field region. Photospheric Zeeman models using a slightly decentered dipole along the axis, z_off_=~0.1R_wd_, B_pole_=~60MG, fit some absorption features in the blue spectral range and confirm the results of high-state cyclotron spectroscopy. The implied distance to RXJ 1938.6-4612 is ~150-190pc.

Publication:

Astronomy and Astrophysics

Pub Date:

January 1995

Bibcode:

1995A&A...293..764S

Keywords: