Detecting Magnetic Fields in Rotationally Perturbed, Hot Stellar Winds

Abstract

ABSTRACT. In this paper, we report on an attempt to optically detect localized and/or variable magnetic fields in the single O4 I(n)f star z Puppis and in the WC 8 star in the binary star g 2 Velorum with the spectropolarimeter Cassegrain echelle spectrograph mounted on the ESO 3.6 m telescope. The spectra cover 5700-6800 Å with resolution element 0.2 Å . These stars are sufficiently bright in principle to obtain Stokes V spectra with excellent signal-to-noise ratio and temporal resolution at this telescope. We discuss several procedures adapted to the extraction of the polarized signal from broad lines to put constraints on the global and local magnetic fields. Despite some instrumental difficulties, we report a null longitudinal component of the global magnetic field measurement in z Pup with G. We also find no significant activity in Stokes V above in10 minutes in z Puppis's observable photospheric lines, in a spectral bandpass of 0.2-3 Å . We also report a null detection above for the emission lines of g Vel. Spectral variability in natural light for these stars is 3j ∼ 0.3% V also discussed. Finally, we discuss the potential of such spectropolarimetric techniques in the context of newgeneration spectropolarimeters.

X‐Ray Modeling of Very Young Early‐Type Stars in the Orion Trapezium: Signatures of Magnetically Confined Plasmas and Evolutionary Implications

“…The X-ray emission sooner or later is fully generated by instabilities in the wind only. Here studies that search for magnetic fields in hot stellar winds (see Chesneau & Moffat 2002) are useful. An intriguing aspect on the Orion stars is that there also seems to exist relatively faint X-ray emission consistent with nonmagnetic wind shocks.…”

THE FIRST SPECTROPOLARIMETRIC MONITORING OF THE PECULIAR O4 Ief SUPERGIANT ζ PUPPIS

“…Moffat & Michaud (1981) detected profile variability with a period of 5.075 days in the depth of the nearly central absorption reversal of the P Cygni type Hα profile in spectrophotometric observations of ζ Pup and proposed that the winds of Oef stars might be shaped by a dipolar stellar magnetic field. Searches for the presence of a magnetic field in ζ Pup were reported by Chesneau & Moffat (2002) and David-Uraz et al (2014). Chesneau & Moffat (2002) used CASPEC observations on four consecutive nights, covering time intervals between 30 and 76 minutes.…”

“…Searches for the presence of a magnetic field in ζ Pup were reported by Chesneau & Moffat (2002) and David-Uraz et al (2014). Chesneau & Moffat (2002) used CASPEC observations on four consecutive nights, covering time intervals between 30 and 76 minutes. The measurements were based on four He lines placed well within the CASPEC orders and not sensitive to defects in the normalization procedure.…”

The Zeeman effect in the Sobolev approximation: applications to spherical stellar winds

“…However, this estimate is highly oversimplified, since instrumental polarization can dominate the noise contribution. Chesneau & Moffat (2002) discuss recent spectropolarimetric observations of hot stars using the ESO 3.6 m, and Donati (2001) and Bagnulo et al (2002) discuss the spectropolarimetric capability of the VLT.It is worth commenting that in principle, the technique of co‐adding line spectra to build up signal in Stokes V , as has been applied to photospheric lines (pioneered by Donati et al 1997), can also be used for wind lines. The basic idea is to add the circularly polarized flux from several lines to increase the S/N ratio in the V ‐signal.…”

“…Many attempts to measure the longitudinal Zeeman effect in these stars have yielded only rather high upper limits of several 100s of gauss (e.g. Chesneau & Moffat 2002, is a recent example; see also the review by Mathys 2002). There have been some detections, notably β Cep (Donati et al 2001) and θ 1 Ori C (Donati & Wade 1999; Donati et al 2002) with surface fields of a few hundred gauss.…”