Low-mass Star-rotation Structure Evolution And Starquake Diagnosis

Rotation periods of many low-mass stars have been measured. The low-mass stars measured rotation periods include PMS stars, MS stars, and subgiants and so on. These observed rotation periods provide us with information on understanding angular momentum evolution. Solar-like oscillations have also been observed in some low-mass stars. We can extract the information on the stellar internal structure that can be used to test and develop our understanding of stellar evolution from these observed oscillation frequencies.Surface helium abundance of the standard solar model constructed in accord with recently observed abundances disagrees with the seismically inferred value. In the standard solar model, rotational effects are ignored. The equations of stellar structure of a rotation star were developed by Kippenhahn & Thomas and Meynet & Maeder. we use the Yale Rotation Evolution Code to construct solar model with low metal abundances. Rotational mixing is used to reconcile the recently observed abundances with helioseismology. We find that the low-helium problem can be solved to a great extent by rotational mixing. However, the angular velocity distribution and the total angular momentum of the Yale rotation model disagree with helioseismical results. We consider effects of magnetic field. Diffusion coefficient for the magnetic angular momentum transport is deduced from the induction and momentum equations. Using this coefficient, we investigate the angular momentum evolution of a star with 1.0 M_⊙. The total angular momentum and the angular velocity distribution in radiative region of magnetic model agree with helioseismical results. We also find that the total angular momentum and the angular velocity distribution of MS stars depend not only on the rate of angular momentum loss but on the efficiency of angular momentum in stellar interior.We also study the frequency separations of stellar p-modes in this thesis. Frequency separation is a powerful tool for extracting the knowledge on the stellar interior structure. A new separationσ_l-1l+1(n), which is similar to the scaled small separations, is obtained from the asymptotic formula of stellar p-modes. The expressions forσ_l-1l+1(n) and the scaled small separations are similar. Just like the scaled small separations,σ_l-1l+1(n) is mainly sensitive to conditions in the stellar core. From our numerical calculation, however, we find thatσ₀₂(n) is more sensitive to the conditions in the stellar core than the scaled small separations and the scaled small separations are more sensitive to the conditions in stellar core thanσ₁₃(n). Thus with the decrease of the central hydrogen abundance of stars, theσ₀₂ andσ₁₃ more and more deviate from the scaled small separations. This characteristic could be used to extract the information on the central hydrogen abundance of stars.