Magnetic field measurements of O stars with FORS 1 at the VLT
Abstract
Context: The presence of magnetic fields in O-type stars has been suspected for a long time. The discovery of these fields would explain a wide range of well documented enigmatic phenomena in massive stars, in particular cyclical wind variability, Hα emission variations, chemical peculiarity, narrow X-ray emission lines, and non-thermal radio/X-ray emission.
Aims: To investigate the incidence of magnetic fields in O stars, we acquired 38 new spectropolarimetric observations with FORS 1 (FOcal Reducer low dispersion Spectrograph) mounted on the 8-m Kueyen telescope of the VLT.
Methods: Spectropolarimetric observations were obtained at different phases for a sample of 13 O stars. Ten stars were observed in the spectral range 348-589 nm, HD 36879 and HD 148937 were observed in the spectral region 325-621 nm, and HD 155806 was observed in both settings. To prove the feasibility of the FORS 1 spectropolarimetric mode for the measurements of magnetic fields in hot stars, we present in addition 12 FORS 1 observations of the mean longitudinal magnetic field in θ1 Ori C and compare them with measurements obtained with the MuSiCoS, ESPaDOnS, and Narval spectropolarimeters.
Results: Most stars in our sample, which were observed on different nights, show a change of the magnetic field polarity, but a field at a significance level of 3σ was detected in only four stars, HD 36879, HD 148937, HD 152408, and HD 164794. The largest longitudinal magnetic field, <B_z> = -276 ± 88 G, was detected in the Of?p star HD 148937. We conclude that large-scale organized magnetic fields with polar field strengths larger than 1 kG are not widespread among O-type stars.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 2008
- DOI:
- 10.1051/0004-6361:200810171
- arXiv:
- arXiv:0808.2039
- Bibcode:
- 2008A&A...490..793H
- Keywords:
-
- polarization;
- stars: early-type;
- stars: atmospheres;
- magnetic fields;
- Astrophysics
- E-Print:
- 8 pages, 4 figures, 3 tables, accepted for publication in A&