392 research outputs found
Discovery of new magnetic early-B stars within the MiMeS HARPSpol survey
To understand the origin of the magnetic fields in massive stars as well as
their impact on stellar internal structure, evolution, and circumstellar
environment, within the MiMeS project, we searched for magnetic objects among a
large sample of massive stars, and build a sub-sample for in-depth follow-up
studies required to test the models and theories of fossil field origins,
magnetic wind confinement and magnetospheric properties, and magnetic star
evolution.
We obtained high-resolution spectropolarimetric observations of a large
number of OB stars thanks to three large programs that have been allocated on
the high-resolution spectropolarimeters ESPaDOnS, Narval, and the polarimetric
module HARPSpol of the HARPS spectrograph. We report here on the methods and
first analysis of the HARPSpol magnetic detections. We identified the magnetic
stars using a multi-line analysis technique. Then, when possible, we monitored
the new discoveries to derive their rotation periods, which are critical for
follow-up and magnetic mapping studies. We also performed a first-look analysis
of their spectra and identified obvious spectral anomalies (e.g., abundance
peculiarities, Halpha emission), which are also of interest for future studies.
In this paper, we focus on eight of the 11 stars in which we discovered or
confirmed a magnetic field from the HARPSpol LP sample (the remaining three
were published in a previous paper). Seven of the stars were detected in
early-type Bp stars, while the last star was detected in the Ap companion of a
normal early B-type star. We report obvious spectral and multiplicity
properties, as well as our measurements of their longitudinal field strengths,
and their rotation periods when we are able to derive them. We also discuss the
presence or absence of Halpha emission with respect to the theory of
centrifugally-supported magnetospheres. (Abriged)Comment: 19 pages, 8 figures, accepted for publication in A&
The magnetic field of the planet-hosting star Bootis
We have obtained high resolution spectropolarimetric data for the
planet-hosting star Bootis, using the ESPaDOnS spectropolarimeter at
CFHT. A weak but clear Stokes signature is detected on three of the four
nights of June 2006 during which we have recorded data. This polarimetric
signature indicates with no ambiguity the presence of a magnetic field at the
star's surface, with intensity of just a few Gauss.
The analysis of the photospheric lines of Boo at ultra-high
signal-to-noise reveals the presence of an 18% relative differential rotation.
Tentative Zeeman-Doppler imaging, using our spectropolarimetric observations
covering only a fraction of the star's rotational phase, indicates a magnetic
field with a dominant potential field component. The data are best fitted when
a 3.1d period of modulation and an intermediate inclination are assumed.
Considering the level of differential rotation of Boo, this implies a
rotation period of 3.0d at the equator and of 3.7d at the pole, and a topology
of the magnetic field where its main non-axisymmetric part is located at low
latitudes.
The planet is probably synchronised with the star's rotation at intermediate
latitudes, while the non-axisymmetric part of the magnetic field seems located
at lower latitudes. Our limited data do not provide sufficient constraints on
the magnetic field to study a possible interaction of the planet with the
star's magnetosphere. Investigating this issue will require data with much
better phase coverage. Similar studies should also be performed for other stars
hosting close-in giant planets.Comment: 6 pages, 4 figures, accepted by MNRA
Mixing and Accretion in lambda Bootis Stars
Strong evidence for deep mixing has been uncovered for slowly rotating F, and
A stars of the main sequence. As the accretion/diffusion model for the
formation of lboo stars is heavily dependent on mixing in superficial regions,
such deep mixing may have important repercussions on our understanding of these
stars. It is shown that deep mixing at a level similar to that of FmAm stars
increases the amount of matter that needs to be accreted by the stars with
respect with the standard models by some three orders of magnitude. It is also
shown that significantly larger accretion rates have to be maintained, as high
as ~M_\sun yr^{-1}, to prevent meridional circulation from
canceling the effect of accretion. The existence of old (~Gyr) is
not a likely outcome of the present models for accretion/diffusion with or
without deep mixing. It is argued that lboo stars are potentially very good
diagnostics of mixing mechanisms in moderately fast rotators.Comment: To appear in Astrophysical Journal Letters. 4 pages, 2 fgure
The 9577 and 9632 Ă Diffuse Interstellar Bands: C60+ as Carrier
Galazutdinov et al. (2017) recently claimed that the relative strengths of the 9577 and 9632 Ă
diffuse interstellar bands (DIBs) are too poorly correlated to be caused by a single source, the C60+ ion. Their conclusion is based on theoretical modeling of contaminating stellar Mg ii lines at 9631.9 and 9632.4 Ă
and UVES spectra. This contradicts their earlier result and those of several others that the two DIBs are closely correlated and, within the errors and effects of stellar blends, exhibit an intensity ratio consistent with that found in the 6 K laboratory spectrum of C60+. We consider the use of close spectral standards to be superior to model atmosphere calculations in correcting for contamination by the Mg ii lines. We have examined some of the same UVES spectra and demonstrate that a lack of suitably observed telluric standards makes it impossible to adequately correct for telluric water vapor contamination, leading to unreliable continuum levels. The possible effects of higher temperatures, in the 30â100 K range, on the C60+ electronic absorption band profiles, and their relative intensities, are also considered
Discovery of magnetic fields in the very young, massive stars W601 (NGC 6611) and OI 201 (NGC 2244)
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.Comment: Accepted for publication as a letter in A&
Gas-phase Absorptions of C60+: A New Comparison with Astronomical Measurements
Campbell et al. recently revised, by a few tenths of an Ă
, the wavelengths for their low-temperature laboratory measurements of fullerene C60+ bands. This accounts for the perturbation caused by the He atom to the C60+-He spectrum. Here, we demonstrate that the revised laboratory wavelengths improve coincidence with the 9632, 9577, 9428, 9365, and 9348 diffuse interstellar bands detected towards the stars HD 46711, HD 169454, and HD 183143
Magnetic cycles of the planet-hosting star tauBootis
We have obtained new spectropolarimetric observations of the planet-hosting
star tauBootis, using the ESPaDOnS and NARVAL spectropolarimeters at the
Canada-France-Hawaii Telescope and Telescope Bernard-Lyot. With this data set,
we are able to confirm the presence of a magnetic field at the surface of
tauBoo and map its large-scale structure over the whole star. The overall
polarity of the magnetic field has reversed with respect to our previous
observation (obtained a year before), strongly suggesting that tauBoo is
undergoing magnetic cycles similar to those of the Sun. This is the first time
that a global magnetic polarity switch is observed in a star other than the
Sun; we speculate that the magnetic cycle period of tauBoo is much shorter than
that of the Sun.
Our new data also allow us to confirm the presence of differential rotation
from the latitudinal shearing that the magnetic structure is undergoing. The
differential rotation surface shear that tauBoo experiences is found to be 6 to
10 times larger than that of the Sun. We propose that the short magnetic cycle
period is due to the strong level of differential rotation. With a rotation
period of 3.0 and 3.9 d at the equator and pole respectively, tauBoo appears as
the first planet-hosting star whose rotation (at intermediate latitudes) is
synchronised with the orbital motion of its giant planet (period 3.3 d).
Assuming that this synchronisation is not coincidental, it suggests that the
tidal effects induced by the giant planet can be strong enough to force the
thin convective enveloppe (though not the whole star) into corotation and thus
to play a role in the activity cycle of tauBoo.Comment: MNRAS, in pres
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
Investigating Ca II emission in the RS CVn binary ER Vulpeculae using the Broadening Function Formalism
The synchronously rotating G stars in the detached, short-period (0.7 d),
partially eclipsing binary, ER Vul, are the most chromospherically active
solar-type stars known. We have monitored activity in the Ca II H & K reversals
for almost an entire orbit. Rucinski's Broadening Function Formalism allows the
photospheric contribution to be objectively subtracted from the highly blended
spectra. The power of the BF technique is also demonstrated by the good
agreement of radial velocities with those measured by others from less crowded
spectral regions. In addition to strong Ca II emission from the primary and
secondary, there appears to be a high-velocity stream flowing onto the
secondary where it stimulates a large active region on the surface 30 - 40
degrees in advance of the sub-binary longitude. A model light curve with a spot
centered on the same longitude also gives the best fit to the observed light
curve. A flare with approximately 13% more power than at other phases was
detected in one spectrum. We suggest ER Vul may offer a magnified view of the
more subtle chromospheric effects synchronized to planetary revolution seen in
certain `51 Peg'-type systems.Comment: Accepted to AJ; 17 pages and 16 figure
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
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