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Bottom (black curves): Examples of two spectra (#1 and #16) of the He i line at 4713 Å obtained at two different phases of the orbital period. The two binary components are indicated (P and S). Top (red curves): disentangled spectra of the He i line at 4713 Å for the primary and secondary components. All spectra are shifted vertically to allow for a better reading.
Source publication
The presence of a magnetic field can have a strong impact on the evolution of
a binary star. However, only a dozen of magnetic OB binaries are known as of
today and available to study this effect, including very few magnetic pulsating
spectroscopic OB binaries. We aim at checking for the presence of a magnetic
field in the B5IV hierarchical triple...
Contexts in source publication
Context 1
... asymmetries are detected in several individual lines of He and Mg in the spectra of HD 1976 (see Fig. 1), sug- gesting a double-lined nature of HD 1976. Similar asymmetries are also seen in the LSD Stokes I profiles (see Sect. 4 ...
Context 2
... obtained consistent results for all considered spectral re- gions and values of the orbital period, i.e. spectral contribution of two stars could be detected in all cases. Fig. 1 spectra of the primary and secondary components. The line pro- file of the secondary component spans about 374 km s −1 and varies significantly in radial velocity, while the profile of the pri- mary spans only about 184 km s −1 and is relatively stable in ra- dial velocity. Therefore, the secondary component is clearly as- sociated to ...
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Context. Oblique magnetic dipole fields have been detected in Bp stars for several decades, and more recently also in normal massive stars. In the past decade, it has been established that stellar magnetospheres form through the channelling and confinement of an outflowing stellar wind by the stellar magnetic field. This explains specific propertie...
Previous studies of the chemically peculiar Bp star 36 Lyn revealed a moderately strong magnetic field, circumstellar material, and inhomogeneous surface abundance distributions of certain elements. We present in this paper an analysis of 33 high-signal-to-noise ratio, high-resolution Stokes IV observations of 36 Lyn obtained with the Narval spectr...
We investigate the magnetic field at the surface of 48 red giants selected as
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Citations
V746 Cas is known to be a triple system composed of a close binary with an alternatively reported period of either 25.4d or 27.8d and a third component in a 62000d orbit. The object was also reported to exhibit multiperiodic light variations with periods from 0.83d to 2.50d, on the basis of which it was classified as a slowly pulsating B star. Interest in further investigation of this system was raised by the detection of a variable magnetic field. Analysing spectra from four instruments, earlier published radial velocities, and several sets of photometric observations, we arrived at the following conclusions: (1) The optical spectrum is dominated by the lines of the B-type primary (Teff1~16500(100) K), contributing 70% of the light in the optical region, and a slightly cooler B tertiary (Teff3~13620(150) K). The lines of the low-mass secondary are below our detection threshold; we estimate that it could be a normal A or F star. (2) We resolved the ambiguity in the value of the inner binary period and arrived at a linear ephemeris of T_super.conj.=HJD 2443838.78(81)+25.41569(42)xE. (3) The intensity of the magnetic field undergoes a~sinusoidal variation in phase with one of the known photometric periods, namely 2.503867(19)d, which we identify with the rotational period of the tertiary. (4) The second photometric 1.0649524(40)d period is identified with the rotational period of the B-type primary, but this interpretation is much less certain and needs further verification. (5) If our interpretation of photometric periods is confirmed, the classification of the object as a slowly pulsating B star should be revised. (6) Applying an N-body model to different types of available observational data, we constrain the orbital inclination of the inner orbit to ~60 deg to 85 deg even in the absence of eclipses, and estimate the probable properties of the triple system and its components.
Until recently almost nothing was known about the evolution of magnetic fields found in upper main sequence Ap/Bp stars during their long main sequence lifetime. We are thus studying magnetic Ap/Bp stars in open clusters in order to obtain observational evidence of how the properties of Ap/Bp magnetic stars, such as field strength and structure, evolve with age during the main sequence. One important aspect of this study is to search for the very rare examples of hot magnetic stars in short-period binary systems among magnetic cluster members. In this paper we characterize the object BD-19~5044L, which is both a member of the open cluster IC 4725 = M~25, and a short-period SB2 system containing a magnetic primary star. We have obtained a series of intensity and circular polarisation spectra distributed through the orbital and rotation cycles of BD-19 5044L with the ESPaDOnS spectropolarimeter at CFHT. We find that the orbit of BD-19 5044L AB is quite eccentric (e = 0.477), with a period of 17.63 d. The primary is a magnetic Bp star with a variable longitudinal magnetic field, a polar field strength of ~1400 G and a low obliquity, while the secondary is probably a hot Am star and does not appear to be magnetic. The rotation period of the primary (5.04 d) is not synchronised with the orbit, but the rotation angular velocity is close to being synchronised with the orbital angular velocity of the secondary at periastron, perhaps as a result of tidal interactions. The periastron separation is small enough (about 12 times the radius of the primary star) that BD-19 5044L may be one of the very rare known cases of a tidally interacting SB2 binary system containing a magnetic Ap/Bp star.
The origin and evolution of magnetism in OB stars is far from being well understood. With approximately 70 magnetic OB stars known, any new object with unusual characteristics may turn out to be a key piece of the puzzle. We report the detection of an exceptionally strong magnetic field in the He-strong B2IV star CPD-62 2124. Spectropolarimetric FORS2 and HARPSpol observations were analysed by two independent teams and procedures, concluding on a strong longitudinal magnetic field of approximately 5.2 kG. The quantitative characterisation of the stellar atmosphere yields an effective temperature of 23650$\pm$250 K, a surface gravity of 3.95$\pm$0.10 dex and a surface helium fraction of 0.35$\pm$0.02 by number. The metal composition is in agreement with the cosmic abundance standard, except for Mg, Si and S, which are slightly non-solar. The strong and broad ($\sim$300 km/s) disc-like emission displayed by the H$\alpha$ line suggests a centrifugal magnetosphere supported by the strong magnetic field. Our results imply that CPD-62 2124 is an early B-type star hosting one of the strongest magnetic fields discovered to date, and one of the most evolved He-strong stars known, with a fractional main-sequence lifetime of approximately 0.6.
A significant fraction of massive main-sequence stars show strong, large-scale magnetic fields. The origin of these fields, their lifetimes, and their role in shaping the characteristics and evolution of massive stars are currently not well understood. We compile a catalogue of 389 massive main-sequence stars, 61 of which are magnetic, and derive their fundamental parameters and ages. The two samples contain stars brighter than magnitude 9 in the V band and range in mass between 5 and 100 Msun. We find that the fractional main-sequence age distribution of all considered stars follows what is expected for a magnitude limited sample, while that of magnetic stars shows a clear decrease towards the end of the main sequence. This dearth of old magnetic stars is independent of the choice of adopted stellar evolution tracks, and appears to become more prominent when considering only the most massive stars. We show that the decreasing trend in the distribution is significantly stronger than expected from magnetic flux conservation. We also find that binary rejuvenation and magnetic suppression of core convection are unlikely to be responsible for the observed lack of older magnetic massive stars, and conclude that its most probable cause is the decay of the magnetic field, over a time span longer than the stellar lifetime for the lowest considered masses, and shorter for the highest masses. We then investigate the spin-down ages of the slowly rotating magnetic massive stars and find them to exceed the stellar ages by far in many cases. The high fraction of very slowly rotating magnetic stars thus provides an independent argument for a decay of the magnetic fields.
Aims. The main-sequence B-type star $\zeta$ Cassiopeiae is known as a N-rich
star with a magnetic field discovered with the Musicos spectropolarimeter. We
model the magnetic field of the star by means of 82 new spectropolarimetric
observations of higher precision to investigate the field strength, topology,
and effect.
Methods. We gathered data with the Narval spectropolarimeter installed at
T\'elescope Bernard Lyot (TBL, Pic du Midi, France) and applied the
least-squares deconvolution technique to measure the circular polarisation of
the light emitted from $\zeta$ Cas. We used a dipole oblique rotator model to
determine the field configuration by fitting the longitudinal field
measurements and by synthesizing the measured Stokes V profiles. We also made
use of the Zeeman-Doppler Imaging technique to map the stellar surface and to
deduce the difference in rotation rate between the pole and equator.
Results. $\zeta$ Cas exhibits a polar field strength $B_{\rm pol}$ of 100-150
G, which is the weakest polar field observed so far in a massive main-sequence
star. Surface differential rotation is ruled out by our observations and the
field of $\zeta$ Cas is strong enough to enforce rigid internal rotation in the
radiative zone according to theory. Thus, the star rotates as a solid body in
the envelope.
Conclusions. We therefore exclude rotationally-induced mixing as the cause of
the surface N-enrichment. We discuss that the transport of chemicals from the
core to the surface by internal gravity waves is the most plausible explanation
for the nitrogen overabundance at the surface of $\zeta$ Cas.
We report the detection of a magnetic field in the helium-strong star CPD-57
3509 (B2 IV), a member of the Galactic open cluster NGC3293, and characterise
the star's atmospheric and fundamental parameters. Spectropolarimetric
observations with FORS2 and HARPSpol are analysed using two independent
approaches to quantify the magnetic field strength. A high-S/N FLAMES/GIRAFFE
spectrum is analysed using a hybrid non-LTE model atmosphere technique.
Comparison with stellar evolution models constrains the fundamental parameters
of the star. We obtain a firm detection of a surface averaged longitudinal
magnetic field with a maximum amplitude of about 1 kG. Assuming a dipolar
configuration of the magnetic field, this implies a dipolar field strength
larger than 3.3 kG. Moreover, the large amplitude and fast variation (within
about 1 day) of the longitudinal magnetic field implies that CPD-57 3509 is
spinning very fast despite its apparently slow projected rotational velocity.
The star should be able to support a centrifugal magnetosphere, yet the
spectrum shows no sign of magnetically confined material; in particular,
emission in H{\alpha} is not observed. Apparently, the wind is either not
strong enough for enough material to accumulate in the magnetosphere to become
observable or, alternatively, some leakage process leads to loss of material
from the magnetosphere. The quantitative spectroscopic analysis of the star
yields an effective temperature and a logarithmic surface gravity of 23750+-250
K and 4.05+-0.10, respectively, and a surface helium fraction of 0.28+-0.02 by
number. The surface abundances of C, N, O, Ne, S, and Ar are compatible with
the cosmic abundance standard, whereas Mg, Al, Si, and Fe are depleted by about
a factor of 2. This abundance pattern can be understood as the consequence of a
fractionated stellar wind. CPD-57 3509 is one of the most evolved He-strong
stars known.
An extremely weak circularly polarized signature was recently discovered in
spectral lines of the chemically peculiar Am star Sirius A. A weak surface
magnetic field was proposed to account for the observed polarized signal, but
the shape of the phase-averaged signature, dominated by a prominent positive
lobe, is not expected in the standard theory of the Zeeman effect. We aim at
verifying the presence of weak circularly polarized signatures in two other
bright Am stars, beta UMa and theta Leo, and investigating the physical origin
of Sirius-like polarized signals further. We present here a set of deep
spectropolarimetric observations of beta UMa and theta Leo, observed with the
NARVAL spectropolarimeter. We analyzed all spectra with the Least Squares
Deconvolution multiline procedure. To improve the signal-to-noise ratio and
detect extremely weak signatures in Stokes V profiles, we co-added all
available spectra of each star (around 150 observations each time). Finally, we
ran several tests to evaluate whether the detected signatures are consistent
with the behavior expected from the Zeeman effect. The line profiles of the two
stars display circularly polarized signatures similar in shape and amplitude to
the observations previously gathered for Sirius A. Our series of tests brings
further evidence of a magnetic origin of the recorded signal. These new
detections suggest that very weak magnetic fields may well be present in the
photospheres of a significant fraction of intermediate-mass stars. The strongly
asymmetric Zeeman signatures measured so far in Am stars (featuring a dominant
single-sign lobe) are not expected in the standard theory of the Zeeman effect
and may be linked to sharp vertical gradients in photospheric velocities and
magnetic field strengths.
The MiMeS (Magnetism in Massive Stars) project is a large-scale, high-resolution, sensitive spectropolarimetric investigation
of the magnetic properties of O- and early B-type stars. Initiated in 2008 and completed in 2013, the project was supported
by three Large Program allocations, as well as various programmes initiated by independent principal investigators, and archival
resources. Ultimately, over 4800 circularly polarized spectra of 560 O and B stars were collected with the instruments ESPaDOnS
(Echelle SpectroPolarimetric Device for the Observation of Stars) at the Canada–France–Hawaii Telescope, Narval at the Télescope
Bernard Lyot and HARPSpol at the European Southern Observatory La Silla 3.6 m telescope, making MiMeS by far the largest systematic
investigation of massive star magnetism ever undertaken. In this paper, the first in a series reporting the general results
of the survey, we introduce the scientific motivation and goals, describe the sample of targets, review the instrumentation
and observational techniques used, explain the exposure time calculation designed to provide sensitivity to surface dipole
fields above approximately 100 G, discuss the polarimetric performance, stability and uncertainty of the instrumentation,
and summarize the previous and forthcoming publications.
About 10$\%$ of the massive main sequence stars have recently been found to
host a strong, large scale magnetic field. Both, the origin and the
evolutionary consequences of these fields are largely unknown. We argue that
these fields may be sufficiently strong in the deep interior of the stars to
suppress convection near the outer edge of their convective core. We performed
parametrised stellar evolution calculations and assumed a reduced size of the
convective core for stars in the mass range 16 M$_{\odot}$ to 28 M$_{\odot}$
from the zero age main sequence until core carbon depletion. We find that such
models avoid the coolest part of the main sequence band, which is usually
filled by evolutionary models that include convective core overshooting.
Furthermore, our `magnetic' models populate the blue supergiant region during
core helium burning, i.e., the post-main sequence gap left by ordinary single
star models, and some of them end their life in a position near that of the
progenitor of Supernova 1987A in the HR diagram. Further effects include a
strongly reduced luminosity during the red supergiant stage, and downward shift
of the limiting initial mass for white dwarf and neutron star formation.
The number of magnetic stars detected among massive stars is small;
nevertheless, the role played by the magnetic field in stellar evolution cannot
be disregarded. Links between line profile variability, enhancements/depletions
of surface chemical abundances, and magnetic fields have been identified for
low-mass B-stars, but for the O-type domain this is almost unexplored. Based on
FORS2 and HARPS spectropolarimetric data, we present the first detection of a
magnetic field in HD54879, a single slowly rotating O9.7 V star. Using two
independent and different techniques we obtained the firm detection of a
surface average longitudinal magnetic field with a maximum amplitude of about
600 G, in modulus. A quantitative spectroscopic analysis of the star with the
stellar atmosphere code FASTWIND results in an effective temperature and a
surface gravity of 33000$\pm1000$ K and 4.0$\pm0.1$ dex. The abundances of
carbon, nitrogen, oxygen, silicon, and magnesium are found to be slightly lower
than solar, but compatible within the errors. We investigate line-profile
variability in HD54879 by complementing our spectra with spectroscopic data
from other recent OB-star surveys. The photospheric lines remain constant in
shape between 2009 and 2014, although H$\alpha$ shows a variable emission. The
H$\alpha$ emission is too strong for a standard O9.7 V and is probably linked
to the magnetic field and the presence of circumstellar material. Its normal
chemical composition and the absence of photospheric line profile variations
make HD54879 the most strongly magnetic, non-variable single O-star detected to
date.
