By Cam: A Multipole Magnetic Field Model

We explain the complex photo-polarimetry variations seen in BY Cam in terms of a multipole magnetic field model (Wu and Wickramasinghe 1992). Based on 54 nights of photometry and 12 nights of polarimetry a new tentative rotational ephemeris is H J D = 2446586.2559417(±10) + 0.13842380E(±58) + 2.89 x 10-10 E(±25). A photometric beat period of 14.11 ± 0.02 days is observed. From narrow emission-line data we derive an orbital period of P orb = 201.30± 0.03 min (c.f., Silber et al. 1992). We show that there is a satisfying consistency among the five observationally determined quantities P spin = 199.3303 ± 0,0004 min (JD=2446586), P orb , P beat , dP spin /dt = 0.132 ± 0.04 sec/year, and dP beat /dt = 0.0125 ± 0.0008 days/year. We thank L. Staufer, R. Remillard and A. Silber for new orbital period and light curve data. This research was supported by LaSpace and NASA grant NAGW 2447 to LSU.