Resumo (PT):
Through the observational study of stellar pulsations, the internal structure of stars can be probed and theoretical models can be tested. The main sequence gamma Doradus (Dor) and delta Scuti (Sct) stars with masses 1.2-2.5 M-circle dot are particularly interesting for asteroseismic study. The gamma Dor stars pulsate in high-order gravity (g) modes, with pulsational periods of order of one day. The delta Sct stars, on the other hand, show low-order g and pressure (p) modes with periods of order of 2 hours. Theory predicts the existence of `hybrid' stars, i.e. stars pulsating in both types of modes, in an overlap region between the instability strips of gamma Dor and delta Sct stars in the Hertzsprung-Russell diagram. Hybrid stars are particularly interesting as the two types of modes probe different regions of the stellar interior and hence provide complementary model constraints. Before the advent of Kepler, only a few hybrid stars had been confirmed. The Kepler satellite is providing a true revolution in the study of and search for hybrid stars. Analysis of the first 50 days of Kepler data of hundreds of gamma Dor and delta Sct candidates reveals extremely rich frequency spectra, with most stars showing frequencies in both the delta Sct and gamma Dor frequency range. As these results show that there are practically no pure delta Sct or gamma Dor pulsators, a new observational classification scheme is proposed by Grigahcene et al. (2010). We present their results and characterize 234 stars in terms of delta Sct, gamma Dor, delta Sct/gamma Dor or gamma Dor/delta Sct hybrids.
Abstract (EN):
Through the observational study of stellar pulsations, the internal structure of stars can be probed and theoretical models can be tested. The main sequence gamma Doradus (Dor) and delta Scuti (Sct) stars with masses 1.2-2.5 M-circle dot are particularly interesting for asteroseismic study. The gamma Dor stars pulsate in high-order gravity (g) modes, with pulsational periods of order of one day. The delta Sct stars, on the other hand, show low-order g and pressure (p) modes with periods of order of 2 hours. Theory predicts the existence of 'hybrid' stars, i.e. stars pulsating in both types of modes, in an overlap region between the instability strips of gamma Dor and delta Sct stars in the Hertzsprung-Russell diagram. Hybrid stars are particularly interesting as the two types of modes probe different regions of the stellar interior and hence provide complementary model constraints. Before the advent of Kepler, only a few hybrid stars had been confirmed. The Kepler satellite is providing a true revolution in the study of and search for hybrid stars. Analysis of the first 50 days of Kepler data of hundreds of gamma Dor and delta Sct candidates reveals extremely rich frequency spectra, with most stars showing frequencies in both the delta Sct and gamma Dor frequency range. As these results show that there are practically no pure delta Sct or gamma Dor pulsators, a new observational classification scheme is proposed by Grigahcene et al. (2010). We present their results and characterize 234 stars in terms of delta Sct, gamma Dor, delta Sct/gamma Dor or gamma Dor/delta Sct hybrids. (C) 2010 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim
Language:
English
Type (Professor's evaluation):
Scientific
No. of pages:
4