Pulsations and orbital modulation of the intermediate polar 1WGA J1958.2+3232

¹ Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK e-mail: A.J.Norton@open.ac.uk; H.Quaintrell@open.ac.uk
² Tuorla Observatory, Turku University, Väisäläntie 20, 21500 Piikkiö, Finland e-mail: sekataja@astro.utu.fi; hlehto@astro.utu.fi
³ NASA Goddard Space Flight Center, Laboratory for High Energy Astrophysics, Code 662, Greenbelt, MD 20771, USA Universities Space Research Association e-mail: mukai@milkyway.gsfc.nasa.gov
⁴ Observatoire Astronomique de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France e-mail: ignacio@isaac.u-strasbg.fr

Corresponding author: A. J. Norton, A.J.Norton@open.ac.uk

Received: 20 November 2001
Accepted: 20 December 2001

Abstract

We present optical photometry, spectroscopy and photopolarimetry, as well as ASCA X-ray observations, of the recently discovered intermediate polar 1WGA J1958.2+3232. Through the first detection of an optical beat frequency, we confirm the previously tentative suggestion that the spin period of the white dwarf is twice the X-ray and optical pulsation period, which we also confirm in each case. We detect an orbital modulation in each of the U, B, V, R and I bands for the first time, and suggest that the true orbital period is the -1d alias of that previously suggested. We also confirm the presence of circular polarization in this system, detecting a variable polarization which has opposite signs in each of the B and R bands. The double peaked pulse profile and oppositely signed polarization pulses suggest that 1WGA J1958.2+3232 accretes onto both magnetic poles via a disc which is truncated relatively close to the white dwarf.