1,721,488 research outputs found
The effect of using different EOS in modelling the α Centauri binary system
Full text linkIn this preliminary study we investigate the effects of using different equations of state (CEFF and OPAL) in the calibration of the binary system α Centauri. Constraints coming from the detection of acoustic oscillations in α Centauri A and B are included in the modelling...
Breaking the core-envelope symmetry in p-mode pulsating stars
No full textIt has been shown that there is a potential ambiguity in the asteroseismic determination of the location of internal structures in a pulsating star (Montgomery et al. 2003). We show how, in the case of high-order non-radial acoustic modes, it is possible to remove this ambiguity by considering modes of different degree. To support our conclusions we have investigated the seismic signatures of sharp density variations in the structure of quasi-homogeneous models
Asteroseismology of solar-type and red-giant stars
No full textWe are entering a golden era for stellar physics driven by satellite and telescope observations of unprecedented quality and scope. New insights on stellar evolution and stellar interiors physics are being made possible by asteroseismology, the study of stars by the observation of natural, resonant oscillations. Asteroseismology is proving to be particularly significant for the study of solar-type and red-giant stars. These stars show rich spectra of solar-like oscillations, which are excited and intrinsically damped by turbulence in the outermost layers of the convective envelopes. In this review we discuss the current state of the field, with a particular emphasis on recent advances provided by the Kepler and COROT (Convection, Rotation & Planetary Transits) space missions and the wider significance to astronomy of the results from asteroseismology, such as stellar populations studies and exoplanet studies. Copyright ©2013 by Annual Reviews. All rights reserved
Asteroseismology of red giants: From analysing light curves to estimating ages
No full textAsteroseismology has started to provide constraints on stellar properties that will be essential to accurately reconstruct the history of the Milky Way. Here we look at the information content in data sets representing current and future space missions (CoRoT, Kepler, K2, TESS, and PLATO) for red giant stars. We describe techniques for extracting the information in the frequency power spectrum and apply these techniques to Kepler data sets of different observing length to represent the different space missions. We demonstrate that for KIC 12008916, a low-luminosity red giant branch star, we can extract useful information from all data sets, and for all but the shortest data set we obtain good constraint on the g-mode period spacing and core rotation rates. We discuss how the high precision in these parameters will constrain the stellar properties of stellar radius, distance, mass and age. We show that high precision can be achieved in mass and hence age when values of the g-mode period spacing are available. We caution that tests to establish the accuracy of asteroseismic masses and ages are still “work in progress”
Constraining fundamental stellar parameters using seismology:Application to α Centauri AB
No full textWe apply the Levenberg-Marquardt minimization algorithm to seismic and classical observables of the
αCen binary system in order to derive the fundamental parameters of αCenA+B, and to analyze the
dependence of these parameters on the chosen observables,
on their uncertainty, and on the physics used in stellar modelling.
We show that while the fundamental stellar parameters do not depend on the treatment of convection adopted
(Mixing Length Theory – MLT – or “Full Spectrum of Turbulence” – FST), the age of the system depends
on the inclusion of gravitational settling, and is
deeply biased by the small frequency separation of component B.
We try to answer the question of the universality of the mixing length parameter, and we find a
statistically reliable dependence of the α-parameter on the HR diagram location
(with a trend similar to the predictions based on 2-D simulations).
We propose the frequency separation ratios as better observables to determine the fundamental stellar parameters, and to use the large frequency
separation and
frequencies to extract information about the stellar structure. The effects of diffusion and equation of state
on the oscillation frequencies are also studied, but present seismic data do not allow their determination
Angular momentum transport in stellar interiors constrained by rotational splittings of mixed modes in red giants
No full textContext. Recent asteroseismic observations have led to the determination of rotational frequency splittings for l = 1 mixed modes in red giants. Aims. We investigate how these observed splittings can constrain the modelling of the physical processes transporting angular momentum in stellar interiors. Methods. We first compare models including a comprehensive treatment of shellular rotation only, with the rotational splittings observed for the red giant KIC 8366239. We then study how these asteroseismic constraints can give us information about the efficiency of an additional mechanism for the internal transport of angular momentum. This is done by computing rotating models of KIC 8366239 that include a constant viscosity corresponding to this physical process, in addition to the treatment of shellular rotation. Results. We find that models of red giant stars including shellular rotation only predict steep rotation profiles, which are incompatible with the measurements of rotational splittings in the red giant KIC 8366239. Meridional circulation and shear mixing alone are found to produce an insufficient internal coupling so that an additional mechanism for the internal transport of angular momentum is needed during the post-main sequence evolution. We show that the viscosity ν add corresponding to this mechanism is strongly constrained to be ν add = 3 × 10 4 cm 2 s -1 thanks to the observed ratio of the splittings for modes in the wings to those at the centre of the dipole forests. Such a value of viscosity may suggest that the same unknown physical process is at work during the main sequence and the post-main sequence evolution. © 2012 ESO
Simulazione di correnti in moto vario su alveo a fondo mobile mediante l’utilizzo di un modello diffusivo e formule di trasporto solido fisicamente basate
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