458 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 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
The magnetic Bp star 36 Lyncis, II. A spectroscopic analysis of its co-rotating disk
We report on the physical properties of the disk-like structure of B8 IIIp
star 36 Lyncis from line syntheses of phase-resolved, high resolution spectra
obtained from the IUE archives and from newly obtained ground-based H
spectra. This disk is highly inclined to the rotational axis and betrays its
existence every half rotation cycle as one of two opposing sectors pass in
front of the star. Although the disk absorption spectrum is at least ten times
too weak to be visible in optical iron lines during these occultations, its
properties can be readily examined in a large number of UV "iron curtain" lines
because of their higher opacities. The analysis of the variations of the UV
resonance lines brings out some interesting details about the radiative
properties of the disks: (1) they are optically thick in the C IV and Si IV
doublets, (2) the range of excitation of the UV resonance lines is larger at
the primary occultation ( = 0.00) than at the secondary one, and (3) the
{\bf relative strengths of the absorption peaks} for the two occultations
varies substantially from line to line. We have modeled the absorptions of the
UV C IV resonance and H absorptions by means of a simulated disk with
opaque and translucent components. Our simulations suggest that a gap separates
the star and the inner edge of the disk. The disk extends radially out to
10 R. The disk scale height perpendicular to the plane is
1R. However, the sector causing the primary occultation is about
four times thicker than the opposite sector. The C IV scattering region extends
to a larger height than the H region does, probably because it results
from shock heating far from the cooler disk plane.Comment: Accepted by Astronomy and Astrophysic
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
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&
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
Searching for links between magnetic fields and stellar evolution. II. The evolution of magnetic fields as revealed by observations of Ap stars in open clusters and associations
The evolution of magnetic fields in Ap stars during the main sequence phase
is presently mostly unconstrained by observation because of the difficulty of
assigning accurate ages to known field Ap stars.
We are carrying out a large survey of magnetic fields in cluster Ap stars
with the goal of obtaining a sample of these stars with well-determined ages.
In this paper we analyse the information available from the survey as it
currently stands.
We select from the available observational sample the stars that are probably
(1) cluster or association members and (2) magnetic Ap stars. For the stars in
this subsample we determine the fundamental parameters T_eff, log(L/L_o), and
M/M_o. With these data and the cluster ages we assign both absolute age and
fractional age (the fraction of the main sequence lifetime completed). For this
purpose we have derived new bolometric corrections for Ap stars.
Magnetic fields are present at the surfaces of Ap stars from the ZAMS to the
TAMS. Statistically for the stars with M > 3 M_o the fields decline with
advancing age approximately as expected from flux conservation together with
increased stellar radius, or perhaps even faster than this rate, on a time
scale of about 3 10^7 yr. In contrast, lower mass stars show no compelling
evidence for field decrease even on a timescale of several times 10^8 yr.
Study of magnetic cluster stars is now a powerful tool for obtaining
constraints on evolution of Ap stars through the main sequence. Enlarging the
sample of known cluster magnetic stars, and obtaining more precise RMS fields,
will help to clarify the results obtained so far. Further field observations
are in progress.Comment: Accepted by Astronomy & Astrophysic
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