11,086 research outputs found
Casimir effect in rugby-ball type flux compactifications
As a continuation of the work in \cite{mns}, we discuss the Casimir effect
for a massless bulk scalar field in a 4D toy model of a 6D warped flux
compactification model,to stabilize the volume modulus. The one-loop effective
potential for the volume modulus has a form similar to the Coleman-Weinberg
potential. The stability of the volume modulus against quantum corrections is
related to an appropriate heat kernel coefficient. However, to make any
physical predictions after volume stabilization, knowledge of the derivative of
the zeta function, (in a conformally related spacetime) is also
required. By adding up the exact mass spectrum using zeta function
regularization, we present a revised analysis of the effective potential.
Finally, we discuss some physical implications, especially concerning the
degree of the hierarchy between the fundamental energy scales on the branes.
For a larger degree of warping our new results are very similar to the previous
ones \cite{mns} and imply a larger hierarchy. In the non-warped (rugby-ball)
limit the ratio tends to converge to the same value, independently of the bulk
dilaton coupling.Comment: 13 pages, 6 figures, accepted for publication in PR
HD66051: the first eclipsing binary hosting an early-type magnetic star
Early-type magnetic stars are rarely found in close binary systems. No such
objects were known in eclipsing binaries prior to this study. Here we
investigated the eclipsing, spectroscopic double-lined binary HD66051, which
exhibits out-of-eclipse photometric variations suggestive of surface brightness
inhomogeneities typical of early-type magnetic stars. Using a new set of
high-resolution spectropolarimetric observations, we discovered a weak magnetic
field on the primary and found intrinsic, element-dependent variability in its
spectral lines. The magnetic field structure of the primary is dominated by a
nearly axisymmetric dipolar component with a polar field strength G and an inclination with respect to the rotation axis of
. A weaker quadrupolar component is also likely to be
present. We combined the radial velocity measurements derived from our spectra
with archival optical photometry to determine fundamental masses (3.16 and 1.75
) and radii (2.78 and 1.39 ) with a 1-3% precision. We also
obtained a refined estimate of the effective temperatures (13000 and 9000 K)
and studied chemical abundances for both components with the help of
disentangled spectra. We demonstrate that the primary component of HD66051 is a
typical late-B magnetic chemically peculiar star with a non-uniform surface
chemical abundance distribution. It is not an HgMn-type star as suggested by
recent studies. The secondary is a metallic-line star showing neither a strong,
global magnetic field nor intrinsic spectral variability. Fundamental
parameters provided by our work for this interesting system open unique
possibilities for probing interior structure, studying atomic diffusion, and
constraining binary star evolution.Comment: 14 pages, 15 figures; accepted for publication in MNRA
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
Magnetic fields, winds and X-rays of the massive stars in the Orion Nebula Cluster
In some massive stars, magnetic fields are thought to confine the outflowing
radiatively-driven wind. Although theoretical models and MHD simulations are
able to illustrate the dynamics of such a magnetized wind, the impact of this
wind-field interaction on the observable properties of a magnetic star - X-ray
emission, photometric and spectral variability - is still unclear. The aim of
this study is to examine the relationship between magnetism, stellar winds and
X-ray emission of OB stars, by providing empirical observations and confronting
theory. In conjunction with the COUP survey of the Orion Nebula Cluster, we
carried out spectropolarimatric ESPaDOnS observations to determine the magnetic
properties of massive OB stars of this cluster.Comment: Proceedings of IAUS272: Active OB star
- …