15,450 research outputs found
Mode stability in delta Scuti stars: linear analysis versus observations in open clusters
A comparison between linear stability analysis and observations of pulsation
modes in five delta Scuti stars, belonging to the same cluster, is presented.
The study is based on the work by Michel et al. (1999), in which such a
comparison was performed for a representative set of model solutions obtained
independently for each individual star considered. In this paper we revisit the
work by Michel et al. (1999) following, however, a new approach which consists
in the search for a single, complete, and coherent solution for all the
selected stars, in order to constrain and test the assumed physics describing
these objects. To do so, refined descriptions for the effects of rotation on
the determination of the global stellar parameters and on the adiabatic
oscillation frequency computations are used. In addition, a crude attempt is
made to study the role of rotation on the prediction of mode instabilities.The
present results are found to be comparable with those reported by Michel et al.
(1999). Within the temperature range log T_eff = 3.87-3.88 agreement between
observations and model computations of unstable modes is restricted to values
for the mixing-length parameter alpha_nl less or equal to 1.50. This indicates
that for these stars a smaller value for alpha_nl is required than suggested
from a calibrated solar model. We stress the point that the linear stability
analysis used in this work still assumes stellar models without rotation and
that further developments are required for a proper description of the
interaction between rotation and pulsation dynamics.Comment: 8 pages, 4 figures, 3 tables. (MNRAS, in press
Recent high resolution laboratory determinations of line broadening and intensity parameters: PH3, CH3D, and CO2
Recent unpublished laboratory work on rovibrational line strengths and broadening coefficients which is of interest in the study of planetary atmospheres was reviewed. The molecules discussed are PH3, CH3D and CO2
Kvantno-elektrodinamičke pospravke za polarizirano Møllerovo raspršenje
Principal contributions to QED radiative effects for Moller scattering of polarized particles are investigated. Explicit formulae for the cross section of radiative effects are given in covariant form. A FORTRAN code based on exact expressions for radiative corrections to cross section was used to calculate the results. Detailed numerical analysis for cross sections as well as for polarization asymmetries is given.Istražuju se glavni doprinosi kvantno-elektrodinamičkih popravaka za Møllerovo raspršenje polariziranih čestica. Izlažu se podrobni ishodi računa za udarne presjeke i polarizacijske asimetrije
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