Title: Overshooting and semiconvection: structural changes
Authors: A. Noels-Grötsch
Affiliation: University of Liège
Abstract:
During central hydrogen burning, the layers located just outside of the
convective core develop a gradient of mean molecular weight whose detailed
profile strongly affect the frequency spectrum.
Processes such as overshooting and semiconvection induce an extramixing,
either a full or a partial mixing.
We discuss the resulting structural changes in MS models of massive stars
and their consequences in post MS stars.
Talk or Poster: talk
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Title: Neutrinos from the Geneva Solar Model
Authors: Abu Kassim, Hasan(1) and Yusof, Norhasliza(1,2)
Affiliation: Department of Physics, University of Malaya, 50603 Kuala Lumpur, Malaysia (1)
Astrophysics Group, EPSAM, Lennard-Jonnes Laboratories, Keele University, ST5 5BG Stafforshire, UK
(2)
Abstract:
In this work, we evolve a solar model using the Geneva stellar evolution code with the most recent thermonuclear reaction rates. We run the code with sufficiently small time steps until it reaches the prescribed solar age. The neutrino luminosity and flux are integrated directly over the standard solar model with another code by using the neutrino production rate which is function of the density, temperature and chemical composition. We compare our result with the solar model by Bahcall and Pinnesoult (2004). We found the neutrino fluxes are consistent with the result predicted by Bahcall and Pinnesoult (2004). A comparison is also made with the experimental fluxes by using a global analysis on the experimental pp, 7Be and 8B neutrino fluxes. Our predicted 8B neutrino flux is consistent with the SNO data.
Talk or Poster: poster
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Title: Differential photometry of delta Scuti stars on Maidanak Observatory
Authors: Ayukov Sergey(1), Artamonov Boris (1), Ezhkova Olga (1), Magnitskiy Aleksander (1), Ehgamberdiev Shuhrat (2), Serebryanskiy Aleksander (2)
Affiliation: 1. Sternberg Astronomical Institute, Moscow State University, Moscow, Russia
2. UBAI, Tashkent, Uzbekistan
Abstract:
Several delta Scuti stars (V350 Peg, V2455 Cyg, V459 Cep) were observed on Maidanak observatory in Uzbekistan in frame of Russian-Uzbek scientific collaboration on asteroseismology. Differential photometry data were obtained on two 60 cm telescopes using CCD. These are pilot observation aimed to estimate instrument and site capabilities for astroseismic observations. Our data indicate that photometry precision is about 0.01 magnitude. We also present results on several observed stars.
Talk or Poster: poster
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Title: Smooth Models of Overshooting at the Base of the Solar Convective Zone
Authors: Baturin V.A. & Mironova I.V.
Affiliation: Sternberg Astronomical Institute, Moscow State University. Russia
Abstract:
We discuss the overshoot layer at the base of the solar convective zone (CZ) and consider a set of possible profiles of the temperature gradient. The main feature of this set is the smoothness of the temperature gradient in the transition layer.
In any solar envelope we can find a point where the Schwarzschild criterion is fulfilled. In classical approach this point is a boundary of convective gradient, as well as a boundary of mixing. Transition overshooting functions are constructed in a circumstance of the Schwarzschild point. We assume that a smooth overshooting between the radiative and convective gradients corresponds to positive flow below the Schwarzschild point. In contrast, the classical overshooting model with negative convective flow assumes the steep temperature gradient. In addition, a smooth transition above the Schwarzschild point could be considered, what corresponds to “undershooting†or suppressed convection near the bottom of CZ.
To study the effect of the temperature gradient on the solar oscillations we calculate the squared Brunt-Vaisala frequency. In model without overshooting the Brunt-Vaisala frequency is almost zero inside CZ and becomes positive below, having the first derivative discontinuity at the boundary. All of smooth functions eliminate the break. But in particular case of the smooth overshooting the Brunt-Vaisala frequency is positive above the Schwarzschild point.
Talk or Poster: poster
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Title: Solar-like oscillations in the $eta$ Cephei V1449 Aql
Authors: Belkacem, K.
Affiliation: University of Liège
Abstract:
The unprecedented high-precision photometric data gathered by the CoRoT mission allow us to report on the detection of convectively excited acoustic modes in a massive star already known to be a $eta$ Cephei type star, V1449 Aql (HD 180642). This star therefore constitutes the prototype of a new class of stars we name {it Chimera}, which pulsate on both solar-like oscillations and opacity-driven ones. This provides a unique opportunity to probe the underlying driving mechanisms, emph{i.e.} turbulent convection and $kappa$-mechanism when simultaneously operating in a single star.
Talk or Poster: talk
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