124 research outputs found
A new seismic analysis of Alpha Centauri
Models of alpha Cen A & B have been computed using the masses determined by
Pourbaix et al. (2002) and the data derived from the spectroscopic analysis of
Neuforge and Magain (1997). The seismological data obtained by Bouchy and
Carrier (2001, 2002) do help improve our knowledge of the evolutionary status
of the system. All the constraints are satisfied with a model which gives an
age of about 6 Gyr for the binary.Comment: to be published in Astronomy and Astrophysic
Thorough analysis of input physics in CESAM and CLES codes
This contribution is not about the quality of the agreement between stellar
models computed by CESAM and CLES codes, but more interesting, on what
ESTA-Task~1 run has taught us about these codes and about the input physics
they use. We also quantify the effects of different implementations of the same
physics on the seismic properties of the stellar models, that in fact is the
main aim of ESTA experiments.Comment: 11 pages, 12 fig. Accepted for publication in ApSS CoRoT/ESTA Volu
Application of time-dependent convection models to the photometric mode identification in gamma Doradus stars
We apply the Time-Dependent Convection (TDC) treatment of Gabriel \cite{Gabriel1996} and Grigahcène et al. \cite{Grigahcene} to the photometric mode identification in gamma Dor stars. Comparison of our theoretical results with the observed amplitudes and phases of the star gamma Dor is presented. This comparison makes the identification of the degree l of its pulsation modes possible and shows that our TDC models better agree with observations than Frozen Convection (FC) models
Higher metal abundances do not solve the solar problem
Context. The Sun acts as a cornerstone of stellar physics. Thanks to
spectroscopic, helioseismic and neutrino flux observations, we can use the Sun
as a laboratory of fundamental physics in extreme conditions. The conclusions
we draw are then used to inform and calibrate evolutionary models of all other
stars in the Universe. However, solar models are in tension with helioseismic
constraints. The debate on the ``solar problem'' has hitherto led to numerous
publications discussing potential issues with solar models and abundances.
Aims. Using the recently suggested high-metallicity abundances for the Sun, we
investigate whether standard solar models, as well as models with macroscopic
transport reproducing the solar surface lithium abundances and analyze their
properties in terms of helioseismic and neutrino flux observations. Methods. We
compute solar evolutionary models and combine spectroscopic and helioseismic
constraints as well as neutrino fluxes to investigate the impact of macroscopic
transport on these measurements. Results. When high-metallicity solar models
are calibrated to reproduce the measured solar lithium depletion, tensions
arise with respect to helioseismology and neutrino fluxes. This is yet another
demonstration that the solar problem is also linked to the physical
prescriptions of solar evolutionary models and not to chemical composition
alone. Conclusions. A revision of the physical ingredients of solar models is
needed in order to improve our understanding of stellar structure and
evolution. The solar problem is not limited to the photospheric abundances if
the depletion of light elements is considered. In addition, tighter constraints
on the solar beryllium abundance will play a key role in the improvement of
solar models.Comment: Accepted for publication in Astronomy and Astrophysic
Evidence for a sharp structure variation inside a red-giant star
The availability of precisely determined frequencies of radial and non-radial
oscillation modes in red giants is finally paving the way for detailed studies
of the internal structure of these stars. We look for the seismic signature of
regions of sharp structure variation in the internal structure of the CoRoT
target HR7349. We analyse the frequency dependence of the large frequency
separation and second frequency differences, as well as the behaviour of the
large frequency separation obtained with the envelope auto-correlation
function. We find evidence for a periodic component in the oscillation
frequencies, i.e. the seismic signature of a sharp structure variation in
HR7349. In a comparison with stellar models we interpret this feature as caused
by a local depression of the sound speed that occurs in the helium
second-ionization region. Using solely seismic constraints this allows us to
estimate the mass (M=1.2^{+0.6}_{-0.4} Msun) and radius (R=12.2^{+2.1}_{-1.8}
Rsun) of HR7349, which agrees with the location of the star in an HR diagram.Comment: 4 pages, 5 figures, accepted in A&A Letter
The CoRoT Evolution and Seismic Tools Activity: Goals and Tasks
The forthcoming data expected from space missions such as CoRoT require the
capacity of the available tools to provide accurate models whose numerical
precision is well above the expected observational errors. In order to secure
that these tools meet the specifications, a team has been established to test
and, when necessary, to improve the codes available in the community. The CoRoT
evolution and seismic tool activity (ESTA) has been set up with this mission.
Several groups have been involved. The present paper describes the motivation
and the organisation of this activity, providing the context and the basis for
the presentation of the results that have been achieved so far. This is not a
finished task as future even better data will continue to demand more precise
and complete tools for asteroseismology.Comment: 11 pages, 3 figures, accepted for publication in Astrophysics and
Space Science, 'CoRoT ESTA' special volum
Solar-like oscillations in a massive star
Seismology of stars provides insight into the physical mechanisms taking
place in their interior, with modes of oscillation probing different layers.
Low-amplitude acoustic oscillations excited by turbulent convection were
detected four decades ago in the Sun and more recently in low-mass
main-sequence stars. Using data gathered by the Convection Rotation and
Planetary Transits mission, we report here on the detection of solar-like
oscillations in a massive star, V1449 Aql, which is a known large-amplitude (b
Cephei) pulsator.Comment: Published in Sience, 19 June 2009, vol. 324, p. 154
Transit confirmation and improved stellar and planet parameters for the super-Earth HD 97658 b and its host star
Super-Earths transiting nearby bright stars are key objects that
simultaneously allow for accurate measurements of both their mass and radius,
providing essential constraints on their internal composition. We present here
the confirmation, based on Spitzer transit observations, that the super-Earth
HD 97658 b transits its host star. HD 97658 is a low-mass
() K1 dwarf, as determined from the Hipparcos
parallax and stellar evolution modeling. To constrain the planet parameters, we
carry out Bayesian global analyses of Keck-HIRES radial velocities, and MOST
and Spitzer photometry. HD 97658 b is a massive () and large ( at 4.5
m) super-Earth. We investigate the possible internal compositions for HD
97658 b. Our results indicate a large rocky component, by at least 60% by mass,
and very little H-He components, at most 2% by mass. We also discuss how future
asteroseismic observations can improve the knowledge of the HD 97658 system, in
particular by constraining its age. Orbiting a bright host star, HD 97658 b
will be a key target for coming space missions TESS, CHEOPS, PLATO, and also
JWST, to characterize thoroughly its structure and atmosphere.Comment: 8 figures, accepted to Ap
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