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

We report on the results of a spectroscopic and photometric study of a new cataclysmic variable, identied as optical counterpart of the X-ray source RX J1554.2+2721 detected by ROSAT. The spectroscopic observations of the relatively bright (16: m 5) object show systematic radial velocity variations with a semi- amplitude of140 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 2: h 753 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 classication is further supported by the soft X-ray spectrum, the characteristic proles of the emission lines, the tomography map and the shape of the orbital light curve. A simple tting 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.