522 research outputs found
Asteroseismology of Massive Stars : Some Words of Caution
Although playing a key role in the understanding of the supernova phenomenon,
the evolution of massive stars still suffers from uncertainties in their
structure, even during their "quiet" main sequence phase and later on during
their subgiant and helium burning phases. What is the extent of the mixed
central region? In the local mixing length theory (LMLT) frame, are there
structural differences using Schwarzschild or Ledoux convection criterion?
Where are located the convective zone boundaries? Are there intermediate
convection zones during MS and post-MS phase, and what is their extent and
location? We discuss these points and show how asteroseismology could bring
some light on these questions.Comment: 10 pages, 5 figures, IAU Symposium 307, New windows on massive stars:
asteroseismology, interferometry, and spectropolarimetry, G. Meynet, C.
Georgy, J.H. Groh & Ph. Stee, ed
Phase diagram of the Kondo necklace: a mean-field renormalization group approach
In this paper we investigate the magnetic properties of heavy fermions in the
antiferromagnetic and dense Kondo phases in the framework of the Kondo necklace
model. We use a mean field renormalization group approach to obtain a
temperature versus Kondo coupling phase diagram for this model in
qualitative agreement with Doniach's diagram, proposed on physical grounds. We
further analyze the magnetically disordered phase using a two-sites approach.
We calculate the correlation functions and the magnetic susceptibility that
allow to identify the crossover between the spin-liquid and the local moment
regimes, which occurs at a {\em coherence} temperature.Comment: 5 figure
Apsidal motion in the massive binary HD152218
Massive binary systems are important laboratories in which to probe the
properties of massive stars and stellar physics in general. In this context, we
analysed optical spectroscopy and photometry of the eccentric short-period
early-type binary HD 152218 in the young open cluster NGC 6231. We
reconstructed the spectra of the individual stars using a separating code. The
individual spectra were then compared with synthetic spectra obtained with the
CMFGEN model atmosphere code. We furthermore analysed the light curve of the
binary and used it to constrain the orbital inclination and to derive absolute
masses of 19.8 +/- 1.5 and 15.0 +/- 1.1 solar masses. Combining radial velocity
measurements from over 60 years, we show that the system displays apsidal
motion at a rate of (2.04^{+.23}_{-.24}) degree/year. Solving the
Clairaut-Radau equation, we used stellar evolution models, obtained with the
CLES code, to compute the internal structure constants and to evaluate the
theoretically predicted rate of apsidal motion as a function of stellar age and
primary mass. In this way, we determine an age of 5.8 +/- 0.6 Myr for HD
152218, which is towards the higher end of, but compatible with, the range of
ages of the massive star population of NGC 6231 as determined from isochrone
fitting.Comment: Accepted for publication in Astronomy & Astrophysic
On the origin of macroturbulence in hot stars
Since the use of high-resolution high signal-to-noise spectroscopy in the
study of massive stars, it became clear that an ad-hoc velocity field at the
stellar surface, termed macroturbulence, is needed to bring the observed shape
of spectral lines into agreement with observations. We seek a physical
explanation of this unknown broadening mechanism. We interprete the missing
line broadening in terms of collective pulsational velocity broadening due to
non-radial gravity-mode oscillations. We also point out that the rotational
velocity can be seriously underestimated whenever the line profiles are fitted
assuming a Gaussian macroturbulent velocity rather than an appropriate
pulsational velocity expression.Comment: To appear in a special volume of the journal Communications in
Asteroseismology dedicated to the Proceedings of the Liege conference; 6
pages, 3 figure
Analysis of tourism settings and management in Caribbean mangroves: case-studies in the French Antilles and in Jamaica
Periodic mass loss episodes due to an oscillation mode with variable amplitude in the hot supergiant HD50064
We aim to interpret the photometric and spectroscopic variability of the
luminous blue variable supergiant HD\,50064 ().CoRoT space photometry
and follow-up high-resolution spectroscopy, with a time base of 137\,d and
169\,d, respectively, was gathered, analysed and interpreted using standard
time series analysis and light curve modelling methods as well as spectral line
diagnostics.The space photometry reveals one period of 37\,d, which undergoes a
sudden amplitude change with a factor 1.6. The pulsation period is confirmed in
the spectroscopy, which additionally reveals metal line radial velocity values
differing by km\,s depending on the spectral line and on the
epoch. We estimate \teff13\,500\,K, \logg1.5 from the equivalent
width of Si lines. The Balmer lines reveal that the star undergoes episodes of
changing mass loss on a time scale similar to the changes in the photometric
and spectroscopic variability, with an average value of (in M\,yr). We tentatively interpret the 37\,d
period as due to a strange mode oscillation.Comment: 4 pages, accepted for publication in Astronomy & Astrophysics Letter
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