1996A&A...313..833T

We report on observations of a new AM Herculis binary identified as the optical counterpart of the X-ray source RX J1957.1-5738, detected during the ROSAT All Sky Survey. It has an orbital period of 99 min and is strongly modulated both in soft X-rays and at optical wavelengths. The source is bright for somewhat less than half the orbital period, suggesting the disappearance of the accretion area behind the horizon of the white dwarf for part of the orbit. During the bright phase the main contribution in the optical appears at red wavelengths which can be explained as cyclotron emission in a relatively low magnetic field. The X-ray spectrum is dominated by a soft quasi-blackbody component, with a smaller contribution from thermal bremsstrahlung. The Hα emission line consists of a broad and a sharp component shifted in phase against each other. The broad component originates in the accretion stream from the low mass companion star, the sharp component on the irradiated surface of the low mass companion. The σ^–, π, and σ⁺ Zeeman absorption components of Hα from a halo around the accretion spot are identified and suggest a magnetic field strength of 16MG. The distance to RX J1957.1-5738 is d∼350 pc.