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New results are described for the use of the Hanle effect in the photospheres of oblique magnetic rotators and of the Zeeman effect in stellar wind emission lines. [ABSTRACT FROM AUTHOR]

Circular polarization from the Zeeman effect is difficult to detect whenever the ratio of the magnetic field strength to the linewidth is small, as might be expected in the winds of hot stars. However, globally structured fields, such as radially swept fields, do present a characteristically complex Zeeman signature that can be distinguished from noise even when small, because of its telltale features that are antisymmetric about the line. If the emission lines are skewed blueward, a signature of photospheric occultation of the redshifted hemisphere, we find that occultation will also reduce the detectability of the Zeeman effect on the red side of the line, further limiting our ability to detect weak magnetic fields in hypersonic winds. Hence, as instrumental precision improves sufficiently, symmetric emission lines will present advantages over lines skewed blueward by occultation, when seeking a Zeeman signal. [ABSTRACT FROM AUTHOR]

The B0.2 V magnetic star τ Sco stands out from the larger population of massive OB stars due to its high X-ray activity, peculiar wind diagnostics and complex magnetic field. Recently, Petit et al. [1] presented the discovery of the first two τ Sco analogues - HD66665 and HD63425, identified by the striking similarity of their UV spectra to that of τ Sco. ESPaDOnS and Narval spectropolarimetric observations were obtained by the Magnetism in Massive Stars CFHT and TBL Large Programs, in order to characterize the stellar and magnetic properties of these stars. A magnetic field of similar surface strength was found on both stars, reinforcing the connection between the presence of a magnetic field and wind peculiarities. We present additional phaseresolved observations secured by the MiMeS collaboration for HD66665 in order to measure its magnetic geometry, and correlate that geometry with diagnostics of mass-loss. [ABSTRACT FROM AUTHOR]

Wolf-Rayet (WR) stars are understood to have clumpy winds [1]. Robert et al. [2] found a statistical relation between the variations of the polarization and the scattering light intensity, R = σp/σphot ≈ 0.05. To explain this result, we propose a model in which clumps are ejected from the surface of WR stars uniformly in space with a Gaussian time interval distribution. According to the observed R along with the subpeaks on the emission lines of WR stars, we can obtain the parameters of the velocity law index β, and of the clump ejection rate in a flow time N. Also, the fraction η of the total mass loss rate contained in the clumps can be found from the observed polarization. [ABSTRACT FROM AUTHOR]

We calculate the circularly polarized Stokes V(λ) profile for emission lines, formed in hot-star winds threaded with a weak split monopole magnetic field. Invoking the weak-field approximation, we find that the V(λ) profile has a characteristic shape with the ubiquitous sign reversal across line center, but also with a sign reveral in each wing. For the optically thin lines treated here, we also conclude that the V(λ) profile integrates to zero on each side of the line separately. The overall scale of V(λ)/I(λ) is set by the ratio of the field strength to the flow speed, B/v, characteristic of the line-forming region, and is of the order of 0.1% for a wind magnetic field B≅100 G at depths where the windspeed is v≅100 km s-1. [ABSTRACT FROM AUTHOR]