RE0751+14, THE 1ST INTERMEDIATE POLAR

We present optical spectroscopy, multicolour photometry and polarimetr y of the new intermediate polar, RE0751 + 14, discovered during the RO SAT WFC survey. The wings of its emission lines exhibit radial velocit y motion with a period approximately 13.9 min, confirming that this is the rotation period of the white dwarf. Intriguingly, the R- and I-ba nd photometric light curves reveal a double-peaked profile at the rota tion period. In contrast, the B-band light curve, at least in our long est (approximately 5 h) time-series in that colour, is apparently domi nated by a 14.5-min, broadly sinusoidal pulsation. There is supporting evidence from a short NOT observation at an earlier epoch that a modu lation with a slightly longer period than the rotation period makes an increasing contribution at blue wavelengths. The 14.5-min variation p robably represents the synodic (beat) period in the system and predict s a binary period of about 5.3 h, consistent with the estimate gleaned from previous spectroscopy. This colour dependence of the period in R E0751 + 14 makes it unique amongst the known intermediate polars. The strongly red colour dependence of the rotational pulsation in RE0751 14 is suggestive of a cyclotron origin, an interpretation supported b y evidence of variable circular polarization in the R-band light from the star. RE0751 + 14 is only the second intermediate polar known to e mit polarized light. As such, the double-peaked nature of the R- and I -band modulations may reflect the effects of cyclotron beaming, rather than the alternative which is that we are witnessing two sites (poles ) of the white dwarf in RE0751 + 14 emitting at red wavelengths. RE075 1 + 14 may well be the first intermediate polar binary with a polar-li ke magnetic field.