The new cataclysmic variable RX J1554.2+2721 in the period gap

¹ Observatorio Astronómico Nacional (Use for smail PO Box 439027, San Diego, CA, 92143-9027, USA.) , Instituto de Astronomía, UNAM, Ensenada, B.C., México
² Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
³ Instituto de Astronomía, UNAM, Apartado Postal 70-264, 04510 México, D.F., México
⁴ Special Astrophysical Observatory of RAS, Nizhnij Arkhyz, 357147, Russia

Corresponding author: G. H. Tovmassian, gag@astrosen.unam.mx

Received: 12 July 2001
Accepted: 24 September 2001

Abstract

We report on the results of a spectroscopic and photometric study of a new cataclysmic variable, identified as optical counterpart of the X-ray source RX J1554.2+2721 detected by ROSAT. The spectroscopic observations of the relatively bright (~165) object show systematic radial velocity variations with a semi-amplitude of ~140 km s^-1. Besides the clear presence of distinct low and high states there are periodic photometric light variations with an amplitude of about 0.15 mag in the R band. The orbital period is 2753 thus being within the period gap, at its upper border. The flux distribution in the spectrum of the object shows a substantial contribution of a M4 v secondary, and also bears clear signs of cyclotron emission. Thus, we classify the discovered object as a new member of the AM Her class of magnetic cataclysmic variables. This classification is further supported by the soft X-ray spectrum, the characteristic profiles of the emission lines, the tomography map and the shape of the orbital light curve. A simple fitting of the spectrum in the low and high states suggests a reduced mass transfer rate in RX J1554.2+2721 compared to similar objects outside the period gap.