The weak magnetic field of the O9.7 supergiant ζ Orionis
We report here the detection of a weak magnetic field of 50–100 G on the O9.7 supergiant ζ Ori A, using spectropolarimetric observations obtained with NARVAL at the 2m Télescope Bernard Lyot atop Pic du Midi (France). ζ Ori A is the third O star known to host a magnetic field (along with θ 1 Ori C a...
| Main Authors: | , , , , , , |
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| Other Authors: | |
| Format: | Text |
| Language: | English |
| Published: |
2008
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| Subjects: | |
| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.311.5964 http://arxiv.org/pdf/0806.2162v1.pdf |
| Summary: | We report here the detection of a weak magnetic field of 50–100 G on the O9.7 supergiant ζ Ori A, using spectropolarimetric observations obtained with NARVAL at the 2m Télescope Bernard Lyot atop Pic du Midi (France). ζ Ori A is the third O star known to host a magnetic field (along with θ 1 Ori C and HD 191612), and the first detection on a ’normal ’ rapidly-rotating O star. The magnetic field of ζ Ori A is the weakest magnetic field ever detected on a massive star. The measured field is lower than the thermal equipartition limit (about 100 G). By fitting NLTE model atmospheres to our spectra, we determined that ζ Ori A is a 40 M ⊙ star with a radius of 25 R⊙and an age of about 5–6 Myr, showing no surface nitrogen enhancement and losing mass at a rate of about 2×10 −6 M ⊙ yr −1. The magnetic topology of ζ Ori A is apparently more complex than a dipole and involves two main magnetic polarities located on both sides of the same hemisphere; our data also suggest that ζ Ori A rotates in about 7.0 d and is about 40 ◦ away from pole-on to an Earth-based observer. Despite its weakness, the detected magnetic field |
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