1,298 research outputs found
Calculation of the average Green's function of electrons in a stochastic medium via higher-dimensional bosonization
The disorder averaged single-particle Green's function of electrons subject
to a time-dependent random potential with long-range spatial correlations is
calculated by means of bosonization in arbitrary dimensions. For static
disorder our method is equivalent with conventional perturbation theory based
on the lowest order Born approximation. For dynamic disorder, however, we
obtain a new non-perturbative expression for the average Green's function.
Bosonization also provides a solid microscopic basis for the description of the
quantum dynamics of an interacting many-body system via an effective stochastic
model with Gaussian probability distribution.Comment: RevTex, no figure
Confirmation of ξ1 CMa's ultra-slow rotation:magnetic polarity reversal and a dramatic change in magnetospheric UV emission lines
Confirmation of ξ1 CMa's ultra-slow rotation:magnetic polarity reversal and a dramatic change in magnetospheric UV emission lines
The magnetic beta Cep pulsator xi^1 CMa has the longest rotational period of
any known magnetic B-type star. It is also the only magnetic B-type star with
magnetospheric emission that is known to be modulated by both rotation and
pulsation. We report here the first unambiguous detection of a negative
longitudinal magnetic field in xi^1 CMa (=-87 +/- 2 G in 2019 and =-207
+/- 3 G in 2020), as well as the results of ongoing monitoring of the star's
Halpha variability. We examine evidence for deviation from a purely dipolar
topology. We also report a new HST UV spectrum of xi^1 CMa obtained near
magnetic null that is consistent with an equatorial view of the magnetosphere,
as evidenced by its similarity to the UV spectrum of beta Cep obtained near
maximum emission. The new UV spectrum of xi^1 CMa provides additional evidence
for the extremely long rotation period of this star via comparison to archival
data.Comment: 13 pages, Accepted 2021 May 14 to Monthly Notices of the Royal
Astronomical Society 202
First evidence of a magnetic field on Vega. Towards a new class of magnetic A-type stars
We report the detection of a magnetic field on Vega through
spectropolarimetric observations. We acquired 257 Stokes V, high
signal-to-noise and high-resolution echelle spectra during four consecutive
nights with the NARVAL spectropolarimeter at the 2-m Telescope Bernard Lyot of
Observatoire du Pic du Midi (France). A circularly polarized signal in line
profiles is unambiguously detected after combining the contribution of about
1200 spectral lines for each spectrum and summing the signal over the 257
spectra. Due to the low amplitude of the polarized signal, various tests have
been performed to discard the possibility of a spurious polarized signal. They
all point towards a stellar origin of the polarized signal. Interpreting this
polarization as a Zeeman signature leads to a value of G for the
disk-averaged line-of-sight component of the surface magnetic field. This is
the first strong evidence of a magnetic field in an A-type star which is not an
Ap chemically peculiar star. Moreover, this longitudinal magnetic field is
smaller by about two orders of magnitude than the longitudinal magnetic field
(taken at its maximum phase) of the most weakly magnetic Ap stars. Magnetic
fields similar to the Vega magnetic field could be present but still undetected
in many other A-type stars.Comment: 4 pages, accepted for publication as a Letter in Astronomy &
Astrophysic
Educational research labs in the Netherlands: a joint venture in connecting the worlds of educational practice and research
The MiMeS Project: Overview and Current Status
The Magnetism in Massive Stars (MiMeS) Project is a consensus collaboration
among many of the foremost international researchers of the physics of hot,
massive stars, with the basic aim of understanding the origin, evolution and
impact of magnetic fields in these objects. At the time of writing, MiMeS Large
Programs have acquired over 950 high-resolution polarised spectra of about 150
individual stars with spectral types from B5-O4, discovering new magnetic
fields in a dozen hot, massive stars. The quality of this spectral and magnetic
mat\'eriel is very high, and the Collaboration is keen to connect with
colleagues capable of exploiting the data in new or unforeseen ways. In this
paper we review the structure of the MiMeS observing programs and report the
status of observations, data modeling and development of related theory.Comment: Proceedings of IAUS272: Active OB star
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