The K-band spectrum of the cataclysmic variable RXJ 0502.8+1624 (Tau 4)

¹ Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK e-mail: S.Littlefair@sheffield.ac.uk
² Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
³ University of Central Florida, Department of Physics, PO Box 162385, Orlando, FL 32816-2385, USA

Received: 28 January 2005
Accepted: 24 March 2005

Abstract

We present the K-band spectrum of the cataclysmic variable RXJ 0502.8+1624 (Tau 4). The spectrum shows a broad, smooth hump, with no absorption lines from the secondary star visible. This result indicates that the infrared light of this system is dominated by cyclotron emission, and, in combination with the optical spectrum and X-ray properties, suggests that Tau 4 is a polar-type cataclysmic variable (CV).
The system was chosen for study because the broadband JHK colours of Tau 4 are consistent with an L-type dwarf, suggesting that this system might harbour an elusive sub-stellar secondary star. The result presented here, along with the recent discovery of cyclotron emission in the cataclysmic variable EF Eri, suggests that care must be taken when using the broadband JHK colours of CVs when targeting searches for sub-stellar secondary stars.