Magnetic Fields in X-Ray Binary Systems

Abstract

The case for variable magnetic fields, in the range 1–15 kG, in three of the X-ray binary candidate stars, is discussed. We refer to electronic Zeeman polarimetry by Kemp and Wolstencroft (1973a and b) and by Angel et al. (1973). Our detections in Hβ showed: (1) definite magnetic fields, roughly constant over periods of 2 h, in θ2 Orionis and HD 77581; and (2) complex time behavior in HD 153919, with field reversals over periods of ~ 10 min, but with usually small values (≲ 2 kG) as averaged over times of 1–2 h. (Photographic Zeeman spectroscopy is therefore unlikely to show detectable fields, i.e. > 2 kG, in the latter star.) The essentially null results of Angel et al. (1973) in Hβ, in HD 77581 and HD 153919, indicate that the emission is non-magnetic; only the underlying absorption (which is far weaker than the emission in Hβ) shows Zeeman effects. A plot of the Zeeman measure for HD 77581, against the 8.95-day period, is shown: our points are suggestive of periodicity; and the points of Angel et al. (1973) which unfortunately have larger relative error bars, are consistent with the indicated variation and with the general scale of our results.