1,154 research outputs found
Investigating the origin of cyclical wind variability in hot, massive stars - I. On the dipolar magnetic field hypothesis
OB stars exhibit various types of spectral variability associated with wind
structures, including the apparently ubiquitous discrete absorption components
(DACs). These are proposed to be caused by either magnetic fields or non-radial
pulsations (NRPs). In this paper, we evaluate the possible relation between
large-scale, dipolar magnetic fields and the DAC phenomenon by investigating
the magnetic properties of a sample of 13 OB stars exhibiting well-documented
DAC behaviour.
Using high-precision spectropolarimetric data acquired in part in the context
of the Magnetism in Massive Stars (MiMeS) project, we find no evidence for
surface dipolar magnetic fields in any of these stars. Using Bayesian
inference, we compute upper limits on the strengths of the fields and use these
limits to assess two potential mechanisms by which the field may influence wind
outflow: magnetic wind confinement and local photospheric brightness
enhancements. Within the limits we derive, both mechanisms fail to provide a
systematic process capable of producing DACs in all of the stars of our sample.
Therefore, this implies that dipolar fields are highly unlikely to be
responsible for these structures in all massive stars, meaning that some other
mechanism must come into play.Comment: 17 pages, 6 figures, accepted for publication in MNRA
The magnetic characteristics of Galactic OB stars from the MiMeS survey of magnetism in massive stars
The Magnetism in Massive Stars (MiMeS) project represents the largest
systematic survey of stellar magnetism ever undertaken. Based on a sample of
over 550 Galactic B and O-type stars, the MiMeS project has derived the basic
characteristics of magnetism in hot, massive stars. Herein we report
preliminary results.Comment: Proceedings of IAUS 302: Magnetic fields throughout stellar evolutio
Confirmation of Ο1 CMa's ultra-slow rotation:magnetic polarity reversal and a dramatic change in magnetospheric UV emission lines
The magnetic beta Cep pulsator xi^1 CMa has the longest rotational period of
any known magnetic B-type star. It is also the only magnetic B-type star with
magnetospheric emission that is known to be modulated by both rotation and
pulsation. We report here the first unambiguous detection of a negative
longitudinal magnetic field in xi^1 CMa (=-87 +/- 2 G in 2019 and =-207
+/- 3 G in 2020), as well as the results of ongoing monitoring of the star's
Halpha variability. We examine evidence for deviation from a purely dipolar
topology. We also report a new HST UV spectrum of xi^1 CMa obtained near
magnetic null that is consistent with an equatorial view of the magnetosphere,
as evidenced by its similarity to the UV spectrum of beta Cep obtained near
maximum emission. The new UV spectrum of xi^1 CMa provides additional evidence
for the extremely long rotation period of this star via comparison to archival
data.Comment: 13 pages, Accepted 2021 May 14 to Monthly Notices of the Royal
Astronomical Society 202
Identification of an ABCB/P-glycoprotein-specific inhibitor of auxin transport by chemical genomics.
The MiMeS Project: Overview and Current Status
The Magnetism in Massive Stars (MiMeS) Project is a consensus collaboration
among many of the foremost international researchers of the physics of hot,
massive stars, with the basic aim of understanding the origin, evolution and
impact of magnetic fields in these objects. At the time of writing, MiMeS Large
Programs have acquired over 950 high-resolution polarised spectra of about 150
individual stars with spectral types from B5-O4, discovering new magnetic
fields in a dozen hot, massive stars. The quality of this spectral and magnetic
mat\'eriel is very high, and the Collaboration is keen to connect with
colleagues capable of exploiting the data in new or unforeseen ways. In this
paper we review the structure of the MiMeS observing programs and report the
status of observations, data modeling and development of related theory.Comment: Proceedings of IAUS272: Active OB star
Magnetic field measurements and wind-line variability of OB-type stars
Context. The first magnetic fields in O- and B-type stars that do not belong
to the Bp-star class, have been discovered. The cyclic UV wind-line
variability, which has been observed in a significant fraction of early-type
stars, is likely to be related to such magnetic fields. Aims. We attempt to
improve our understanding of massive-star magnetic fields, and observe
twenty-five carefully-selected, OB-type stars. Methods. Of these stars we
obtain 136 magnetic field strength measurements. We present the UV wind-line
variability of all selected targets and summarise spectropolarimetric
observations acquired using the MUSICOS spectropolarimeter, mounted at the TBL,
Pic du Midi, between December 1998 and November 2004. From the average Stokes I
and V line profiles, derived using the LSD method, we measure the magnetic
field strengths, radial velocities, and first moment of the line profiles.
Results. No significant magnetic field is detected in any OB-type star that we
observed. Typical 1{\sigma} errors are between 15 and 200 G. A possible
magnetic-field detection for the O9V star 10 Lac remains uncertain, because the
field measurements depend critically on the fringe- effect correction in the
Stokes V spectra. We find excess emission in UV-wind lines, centred about the
rest wavelength, to be a new indirect indicator of the presence of a magnetic
field in early B-type stars. The most promising candidates to host magnetic
fields are the B-type stars {\delta} Cet and 6 Cep, and a number of O stars.
Conclusions. Although some O and B stars have strong dipolar field, which cause
periodic variability in the UV wind-lines, such strong fields are not
widespread. If the variability observed in the UV wind-lines of OB stars is
generally caused by surface magnetic fields, these fields are either weak
(<~few hundred G) or localised.Comment: A&A publishe
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