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Astron. Astrophys. 348, 861-867 (1999)

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Zeeman lines and a single cyclotron line in the low-accretion rate polar 1RXS J012851.9-233931 (RBS0206) *

A.D. Schwope 1, R. Schwarz 1 and J. Greiner 1

Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany

Received 31 March 1999 / Accepted 28 June 1999

Abstract

We present a low-resolution discovery spectrum and CCD-photometry of the bright X-ray source 1RXS J012851.9-233931 found in the ROSAT All-Sky Survey. These first observations suggest that the source is an AM Herculis star (polar) accreting at a low rate. The optical spectrum is dominated by Zeeman absorption features from the white dwarf, indicating a mean photospheric magnetic field of [FORMULA] MG. Only weak Balmer line emission was observed. In the near infra-red, a single intense cyclotron hump was observed. The inferred magnetic field strength in the accretion plama is [FORMULA] MG, the temperature in the plasma is below 2 keV. Likely orbital periods are [FORMULA]90 min or [FORMULA]146 min, the latter inside the cataclysmic variable period gap. The system is an ideal target for further detailed investigations of the field structure on a magnetic white dwarf by phase-resolved spectropolarimetry.

Key words: accretion, accretion disks – stars: novae, cataclysmic variables – stars: individual: 1RXS J012851.9 – 233931 – stars: magnetic fields

* Based on observations at the European Southern Observatory La Silla (Chile)

Send offprint requests to: Axel D. Schwope

Correspondence to: ASchwope@aip.de

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© European Southern Observatory (ESO) 1999

Online publication: August 13, 199
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