RX J2133.7+5107: identification of a new long period Intermediate Polar

¹ Service d'Astrophysique, DSM/DAPNIA/SAp, CE Saclay, 91191 Gif-sur-Yvette Cedex, France e-mail: bonnetbidaud@cea.fr
² LUTH (CNRS-UMR 8102), Observatoire de Paris, Section de Meudon, 92195 Meudon Cedex, France
³ APC (CNRS-UMR 7164), Université Denis Diderot, 2 place Jussieu, 75005 Paris, France e-mail: martine.mouchet@obspm.fr
⁴ INAF - Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy e-mail: demartino@na.astro.it
⁵ Observatoire Astronomique de Strasbourg, 67000 Strasbourg, France e-mail: motch@astro.u-strasbg.fr

Received: 25 April 2005
Accepted: 20 July 2005

Abstract

We report the first time-resolved photometric and spectroscopic optical observations of the X-ray source RX J2133.7+5107, identified in the ROSAT survey. A clear persistent optical light pulsation is discovered with fast photometry at a period of  s which we associate with the spin period of an accreting white dwarf. Radial velocity curves of the strong emission lines show modulation with a period of  h, identified as the orbital period. These observations establish that the source is a member of the intermediate polar class (IPs) of magnetic cataclysmic variables. With only 4 IPs with longer orbital periods, RX J2133.7+5107  is among the widest systems. It is a unique IP with an orbital period in the middle of the so-called (6-10) h IP gap and it shows a significant degree of asynchronism with a ratio / of 0.02. When attributed to the motion of the white dwarf, the emission lines orbital modulation yields a mass function of   which, for a probable inclination  and a white dwarf mass , corresponds to a secondary mass  .