Exploring the origin of magnetic fields in massive stars.
II. New magnetic field measurements in cluster and field stars
Hubrig, S.; Schöller, M.; Ilyin, I.; Kharchenko, N. V.; Oskinova, L. M.; Langer, N.; Gonzalez, J. F.; Kholtygin, A. F.; Briquet, M.; Magori Collaboration
Context. Theories on the origin of magnetic fields in massive stars
remain poorly developed, because the properties of their magnetic field
as function of stellar parameters could not yet be investigated.
Additional observations are of utmost importance to constrain the
conditions that are conducive to magnetic fields and to determine first
trends about their occurrence rate and field strength distribution.
Aims: To investigate whether magnetic fields in massive stars are
ubiquitous or appear only in stars with a specific spectral
classification, certain ages, or in a special environment, we acquired
67 new spectropolarimetric observations for 30 massive stars. Among the
observed sample, roughly one third of the stars are probable members of
clusters at different ages, whereas the remaining stars are field stars
not known to belong to any cluster or association.
Methods: Spectropolarimetric observations were obtained during four
different nights using the low-resolution spectropolarimetric mode of
FOcal Reducer low dispersion Spectrograph (FORS 2) mounted on the 8-m
Antu telescope of the VLT. Furthermore, we present a number of follow-up
observations carried out with the high-resolution spectropolarimeters
SOFIN mounted at the Nordic Optical Telescope (NOT) and HARPS mounted at
the ESO 3.6 m between 2008 and 2011. To assess the membership in open
clusters and associations, we used astrometric catalogues with the
highest quality kinematic and photometric data currently available.
Results: The presence of a magnetic field is confirmed in nine stars
previously observed with FORS 1/2: HD 36879, HD 47839, CPD-28 2561,
CPD-47 2963, HD 93843, HD 148937, HD 149757, HD 328856, and HD 164794.
New magnetic field detections at a significance level of at least 3#
were achieved in five stars: HD 92206c, HD 93521, HD 93632, CPD-46 8221,
and HD 157857. Among the stars with a detected magnetic field, five
stars belong to open clusters with high membership probability.
According to previous kinematic studies, five magnetic O-type stars in
our sample are candidate runaway stars.
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