HOWELL S.B., HARRISON T.E., HUBER M.E., SZKODY P., WALTER F.M. and HARBECK D.
Abstract (from CDS):
We present new optical photometric and spectroscopic observations and K-band spectroscopy of two magnetic interacting binaries: Tau 4 (RXJ0502.8+1624) and SDSS J121209.31+013627.7. Tau 4 shows short-term, highly modulated optical light but no orbital period is firmly detected. K-band spectroscopy shows H and He I emission and reveals a remarkable phase-resolved dataset. We detect clear evidence for cyclotron humps in the K-band implying a magnetic white dwarf with B ∼ 7-11 MG and confirming Tau 4 as a magnetic binary. A short self eclipse by the gas stream is evident as the spectrum changes from emission to absorption and back within a few minutes. None of our K-band spectra of Tau 4 appear similar to the previously reported observation. Optical spectroscopy of SDSS J121209.31+013627.7 in 2007 May and June shows Zeeman-split Balmer absorption lines as previously noted in the literature but only weak, sporadic Hα emission compared to past data. However, stronger Hα emission returned in 2008 February, looking similar to that previously detected in 2006. The variable nature of this emission line makes irradiation from the white dwarf an unlikely cause of the Hα emission in J1212. The nature of J1212 is reminiscent of that observed in its near twin, EF Eri.