Yazar "Inlek, G." seçeneğine göre listele

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    Öğe
    Absolute parameters of young stars - II. V831 Centauri
    (Oxford Univ Press, 2010) Budding, E.; Erdem, A.; Inlek, G.; Demircan, O.
    Literature photometry and new high-resolution spectroscopy of V831 Cen are presented and analysed. Light and radial velocity curve fittings confirm the central pair of this young multiple system to be close to contact. Absolute parameters are found as follows: M-1 = 4.08 +/- 0.07 M-circle dot, M-2 = 3.35 +/- 0.06 M-circle dot, R-1 = 2.38 +/- 0.03 R-circle dot, R-2 = 2.25 +/- 0.03 R-circle dot, T-1 = 13 000 +/- 300 K, T-2 = 11 800 +/- 300 K; distance of 110 +/- 10 pc and age of similar to 20 +/- 5 Myr. Detailed examination of the spectrograms indicates the third component (V831 Cen B) to be an Ap star. The orbit of the third star about the close binary is analysed using historic astrometric measurements. This allows an estimate of the third star's mass to be about 2.5 M-circle dot, but this is sensitive to the adopted distance and inclination values. It is, however, confirmed by the measured radial velocity of the third star. To some extent, such analysis can also be applied to the fourth star (V831 Cen C). The derived properties can be checked against the system's membership of the Scorpius-Centaurus OB2 association.
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    Öğe
    The role of stellar envelope convection in gravity-darkening and its relation to observational data
    (Elsevier, 2007) Inlek, G.; Boke, A.; Yilmaz, O.; Budding, E.
    We study the role of convection in the surface heat flow of low mass stellar envelopes with the aid of Paczynski's public domain program program GOB. This role is important, for example, for the analysis of light curves of close binary stars. We have considered atrnospheric models for a range of masses similar to the components of contact or near-contact binaries between 0.4 and 1.1 M-circle dot, and examined the effects of changing luminosity, surface temperature and mixing length for stars of given mass. Our presentation includes checks of the modeling against published standard stellar envelopes. A slight program modification allowed gravity darkening coefficients for selected models to be calculated directly. If the procedure proposed by Lucy is followed, similar values of the index beta(similar to 0.06-0.1) are obtained for a fairly wide range of masses, luminosities and effective temperatures of cool stars. There also appears no strong dependence on the mixing-length parameter alpha. There are, however, physical differences between the conditions that apply to this derivation of the index and those of a photosphere distorted by rotation and tides, but having net dynamical stability. Thus, the dependency of T-e on g was argued to come from the ratio of partial derivatives of the adiabatic constant K for the layer where convection starts; but a subconvective equipotential surface, where K would be constant, cannot coincide with such a layer. The adopted procedure is therefore inappropriate, and would involve different heat transfer regimes in different radial directions (say, polar or equatorial). A corresponding evaluation for the layer in which the convective flux becomes maximal shows less sensitivity to T-e The corresponding index is then much closer to, or even greater than, the von Zeipel value. Other arauments are also considered, including those of Anderson and Shu [Anderson, L.. Shu, F.H., 1977. ApJ 214, 798] about the independence of the convective flux to local gravity, as well as the role of superphotospheric circulation effects, which could reduce the gravity darkening index to less than its subphotospheric value. Observational evaluations of gravity darkening for close binary systems, in general, are still inconclusive, due to the strong correlation between beta and other parameters characterizing the light curve shape, particularly in the scale photometric 'ellipticity' effects. It is possible that very precise light curves that may be obtained in the future will allow this situation to be improved. The general surface distribution of emergent flux in the far infra-red of Jupiter may be a pointer in the direction of future studies of the subject. (c) 2006 Elsevier B.V. All rights reserved.