25 research outputs found
The "Binarity and Magnetic Interactions in various classes of Stars" (BinaMIcS) project
The "Binarity and Magnetic Interactions in various classes of stars"
(BinaMIcS) project is based on two large programs of spectropolarimetric
observations with ESPaDOnS at CFHT and Narval at TBL. Three samples of
spectroscopic binaries with two spectra (SB2) are observed: known cool magnetic
binaries, the few known hot magnetic binaries, and a survey sample of hot
binaries to search for additional hot magnetic binaries. The goal of BinaMIcS
is to understand the complex interplay between stellar magnetism and binarity.
To this aim, we will characterise and model the magnetic fields, magnetospheric
structure and coupling of both components of hot and cool close binary systems
over a significant range of evolutionary stages, to confront current theories
and trigger new ones. First results already provided interesting clues, e.g.
about the origin of magnetism in hot stars.Comment: 4 pages, 2 figures, proceedings of the SF2A conferenc
Roadmap on the theoretical work of BinaMIcS
We review the different theoretical challenges concerning magnetism in
interacting binary or multiple stars that will be studied in the BinaMIcS
(Binarity and Magnetic Interactions in various classes of Stars) project during
the corresponding spectropolarimetric Large Programs at CFHT and TBL. We
describe how completely new and innovative topics will be studied with BinaMIcS
such as the complex interactions between tidal flows and stellar magnetic
fields, the MHD star-star interactions, and the role of stellar magnetism in
stellar formation and vice versa. This will strongly modify our vision of the
evolution of interacting binary and multiple stars.Comment: 2 pages, proceeding of IAUS 302 Magnetic fields throughout stellar
evolution, correct list of author
The magnetic field of the double-lined spectroscopic binary system HD 5550
(Abridged) In the framework of the BinaMicS project, we have begun a study of
the magnetic properties of a sample of intermediate-mass and massive
short-period binary systems, as a function of binarity properties. We report in
this paper the characterisation of the magnetic field of HD 5550, a
double-lined spectroscopic binary system of intermediate-mass, using
high-resolution spectropolarimetric Narval observations of HD 5550. We first
fit the intensity spectra using Zeeman/ATLAS9 LTE synthetic spectra to estimate
the effective temperatures, microturbulent velocities, and the abundances of
some elements of both components, as well as the light-ratio of the system. We
then fit the least-square deconvolved profiles to determine the radial and
projected rotational velocities of both stars. We then analysed the shape and
evolution of the LSD profiles using the oblique rotator model to
characterise the magnetic fields of both stars.
We confirm the Ap nature of the primary, previously reported in the
literature, and find that the secondary displays spectral characteristics
typical of an Am star. While a magnetic field is clearly detected in the lines
of the primary, no magnetic field is detected in the secondary, in any of our
observation. If a dipolar field were present at the surface of the Am star, its
polar strength must be below 40 G. The faint variability observed in the Stokes
profiles of the Ap star allowed us to propose a rotation period of
d, close to the orbital period (6.82 d),
suggesting that the star is synchronised with its orbit. By fitting the
variability of the profiles, we propose that the Ap component hosts a
dipolar field inclined with the rotation axis at an angle
and a polar strength G. The field strength is
the weakest known for an Ap star.Comment: 13 pages, 12 figures, accepted for publication in Astronomy &
Astrophysic
How unique is Plaskett's star? A search for organized magnetic fields in short period, interacting or post-interaction massive binary systems
Amongst O-type stars with detected magnetic fields, the fast rotator in the
close binary called Plaskett's star shows a variety of unusual properties.
Since strong binary interactions are believed to have occurred in this system,
one may wonder about their potential role in generating magnetic fields. Stokes
V spectra collected with the low-resolution FORS2 and high-resolution ESPaDOnS
and Narval spectropolarimeters were therefore used to search for magnetic
fields in 15 interacting or post-interaction massive binaries. No magnetic
field was detected in any of them, with 0G always being within 2sigma of the
derived values. For 17 out of 25 stars in the systems observed at
high-resolution, the 90% upper limit on the individual dipolar fields is below
the dipolar field strength of Plaskett's secondary; a similar result is found
for five out of six systems observed at low resolution. If our sample is
considered to form a group of stars sharing similar magnetic properties, a
global statistical analysis results in a stringent upper limit of ~200G on the
dipolar field strength. Moreover, the magnetic incidence rate in the full
sample of interacting or post-interaction systems (our targets + Plaskett's
star) is compatible with that measured from large surveys, showing that they
are not significantly different from the general O-star population. These
results suggest that binary interactions play no systematic role in the
magnetism of such massive systems.Comment: 11 pages, accepted for publication in MNRA
The BinaMIcS project: understanding the origin of magnetic fields in massive stars through close binary systems
It is now well established that a fraction of the massive (M>8 Msun) star
population hosts strong, organised magnetic fields, most likely of fossil
origin. The details of the generation and evolution of these fields are still
poorly understood. The BinaMIcS project takes an important step towards the
understanding of the interplay between binarity and magnetism during the
stellar formation and evolution, and in particular the genesis of fossil
fields, by studying the magnetic properties of close binary systems. The
components of such systems are most likely formed together, at the same time
and in the same environment, and can therefore help us to disentangle the role
of initial conditions on the magnetic properties of the massive stars from
other competing effects such as age or rotation. We present here the main
scientific objectives of the BinaMIcS project, as well as preliminary results
from the first year of observations from the associated ESPaDOnS and Narval
spectropolarimetric surveys.Comment: To appear in New Windows on Massive Stars, proceedings of the IAU
Symposium 30
The large-scale magnetic field of the M dwarf double-line spectroscopic binary FK Aqr
This work is part of the BinaMIcS project, the aim of which is to understand
the interaction between binarity and magnetism in close binary systems. All the
studied spectroscopic binaries targeted by the BinaMIcS project encompass hot
massive and intermediate-mass stars on the main sequence, as well as cool stars
over a wide range of evolutionary stages. The present paper focuses on the
binary system FK Aqr, which is composed of two early M dwarfs. Both stars are
already known to be magnetically active based on their light curves and
detected flare activity. In addition, the two components have large convective
envelopes with masses just above the fully convective limit, making the system
an ideal target for studying effect of binarity on stellar dynamos. We use
spectropolarimetric observations obtained with ESPaDOnS at CFHT in September
2014. Mean Stokes I and V line profiles are extracted using the least-squares
deconvolution (LSD) method. The radial velocities of the two components are
measured from the LSD Stokes I profiles and are combined with interferometric
measurements in order to constrain the orbital parameters of the system. The
longitudinal magnetic fields Bl and chromospheric activity indicators are
measured from the LSD mean line profiles. The rotational modulation of the
Stokes V profiles is used to reconstruct the surface magnetic field structures
of both stars via the Zeeman Doppler imaging (ZDI) inversion technique. Maps of
the surface magnetic field structures of both components of FK Aqr are
presented for the first time. Our study shows that both components host similar
large-scale magnetic fields of moderate intensity (Bmean ~ 0.25 kG); both are
predominantly poloidal and feature a strong axisymmetric dipolar component.
(abridged)Comment: 19 pages, 6 figures, 6 tables + appendices, accepted for publication
in A&A, in pres
Investigating the origin of the spectral line profiles of the Hot Wolf-Rayet Star WR 2
The hot WN star WR 2 (HD 6327) has been claimed to have many singular characteristics. To explain its unusually rounded and relatively weak emission line profiles, it has been proposed that WR 2 is rotating close to break-up with a magnetically confined wind. Alternatively, the line profiles could be explained by the dilution of WR 2’s spectrum by that of a companion. In this paper, we present a study of WR 2 using near-infrared AO imaging and optical spectroscopy and polarimetry. Our spectra reveal the presence of weak photospheric absorption lines from a ∼B 2.5-4V companion, which however contributes only ∼5–10% to the total light, suggesting that the companion is a background object. Therefore, its flux cannot be causing any significant dilution of the WR star’s emission lines. The absence of intrinsic linear continuum polarization from WR 2 does not support the proposed fast rotation. Our Stokes V spectrum was not of sufficient quality to test the presence of a moderately strong organized magnetic field but our new modelling indicates that to confine the wind the putative magnetic field must be significantly stronger than was previously suggested sufficiently strong as to make its presence implausible