129 research outputs found
Magnetic field detection in the B2Vn star HR 7355
The B2Vn star HR 7355 is found to be a He-rich magnetic star.
Spectropolarimetric data were obtained with FORS1 at UT2 on Paranal observatory
to measure the disk-averaged longitudinal magnetic field at various phases of
the presumed 0.52 d cycle. A variable magnetic field with strengths between B_z
= -2200 and +3200G was found, with confidence limits of 100 to 130G. The field
topology is that of an oblique dipole, while the star itself is seen about
equator-on. In the intensity spectra the HeI-lines show the typical equivalent
width variability of He-strong stars, usually attributed to surface abundance
spots. The amplitudes of the equivalent width variability of the HeI lines are
extraordinarily strong compared to other cases. These results not only put HR
7355 unambiguously among the early-type magnetic stars, but confirm its
outstanding nature: With v sin i = 320 km/s the parameter space in which
He-strong stars are known to exist has doubled in terms of rotational velocity.Comment: 6 pages, 5 figures, 1 Table. Accepted for publication in MNRAS
Letter
The (B0+?)+O6 system FN CMa: A case for tidal-pulsational interaction?
FN CMa is visually double with a separation of about 0.6arcsec. Sixty
high-cadence VLT/UVES spectra permit the A and B components to be disentangled,
as the relative contribution of each star to the total light entering the
spectrograph fluctuates between exposures due to changes in seeing. Component A
exhibits rapid line-profile variations, leading us to attribute the photometric
variability seen by HIPPARCOS (with a derived P=0.08866d) to this component.
From a total of 122 archival and new echelle spectra it is shown that component
A is an SB1 binary with an orbital period of 117.55 days. The eccentricity of
0.6 may result in tidal modulation of the pulsation(s) of component Aa.Comment: 2 pages, 1 figure, IAUS 272 - Active OB Stars: Structure, Evolution,
Mass Loss and Critical Limit
The magnetic field of zeta Orionis A
Zeta Ori A is a hot star claimed to host a weak magnetic field, but no clear
magnetic detection was obtained so far. In addition, it was recently shown to
be a binary system composed of a O9.5I supergiant and a B1IV star. We aim at
verifying the presence of a magnetic field in zeta Ori A, identifying to which
of the two binary components it belongs (or whether both stars are magnetic),
and characterizing the field.Very high signal-to-noise spectropolarimetric data
were obtained with Narval at the Bernard Lyot Telescope (TBL) in France.
Archival HEROS, FEROS and UVES spectroscopic data were also used. The data were
first disentangled to separate the two components. We then analyzed them with
the Least-Squares Deconvolution (LSD) technique to extract the magnetic
information. We confirm that zeta Ori A is magnetic. We find that the
supergiant component zeta Ori Aa is the magnetic component: Zeeman signatures
are observed and rotational modulation of the longitudinal magnetic field is
clearly detected with a period of 6.829 d. This is the only magnetic O
supergiant known as of today. With an oblique dipole field model of the Stokes
V profiles, we show that the polar field strength is ~ 140 G. Because the
magnetic field is weak and the stellar wind is strong, zeta Ori Aa does not
host a centrifugally supported magnetosphere. It may host a dynamical
magnetosphere. Its companion zeta Ori Ab does not show any magnetic signature,
with an upper limit on the undetected field of 300 G
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