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arXiv · 0802.4078

Discovery of magnetic fields in the very young, massive stars W601 (NGC 6611) and OI 201 (NGC 2244)

E. Alecian·G. A. Wade·C. Catala·S. Bagnulo·T. Boehm·D. Bohlender·J. -C. Bouret·J. -F. Donati·C. P. Folsom·J. Grunhut·J. D. Landstreet
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Abstract

Context: Recent spectropolarimetric observations of Herbig Ae/Be stars have yielded new arguments in favour of a fossil origin for the magnetic fields of intermediate mass stars. Aims: To study the evolution of these magnetic fields, and their impact on the evolution of the angular momentum of these stars during the pre-main sequence phase, we observed Herbig Ae/Be members of young open clusters of various ages. Methods: We obtained high-resolution spectropolarimetric observations of Herbig Ae/Be stars belonging to the young open clusters NGC 6611 (< 6 Myr), NGC 2244 (~1.9 Myr), and NGC 2264 (~8 Myr), using ESPaDOnS at theCanada-France-Hawaii Telescope. Results: Here we report the discovery of strong magnetic fields in two massive pre-main sequence cluster stars. We detected, for the first time, a magnetic field in a pre-main sequence rapid rotator: the 10.2 Msun Herbig B1.5e star W601 (NGC 6611; v sin i ~ 190 km/s). Our spectropolarimetric observations yield a longitudinal magnetic field larger than 1 kG, and imply a rotational period shorter than 1.7 days. The spectrum of this very young object (age ~ 0.017 Myr) shows strong and variable lines of He and Si. We also detected a magnetic field in the 12.1 Msun B1 star OI 201 (NGC 2244; v sin i = 23.5 km/s). The Stokes V profile of this star does not vary over 5 days, suggesting a long rotational period, a pole-on orientation, or aligned magnetic and rotation axes. OI 201 is situtated near the Zero-Age Main Sequence on the HR diagram, and exhibits normal chemical abundances and no spectrum variability.

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E. Alecian, G. A. Wade, C. Catala, S. Bagnulo, T. Boehm, D. Bohlender, J. -C. Bouret, J. -F. Donati, C. P. Folsom, J. Grunhut, J. D. Landstreet. 2008-02-27. Discovery of magnetic fields in the very young, massive stars W601 (NGC 6611) and OI 201 (NGC 2244). https://doi.org/10.1051/0004-6361:200809444

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