Long Period Variable Star Evolution And Vibration

In this thesis we have calculated the evolution models and the pulsating property of 15M? 2OM0and 30M畇tars under different metal I icity, in order to understand the dependence of the per iod條uminosity relation on metal I icity. Up梩o梔ate opacities, overshootingfrom the convective core and mass loss through the stellar wind was included in our evolution models. In order to get better agreement with the observed blue梩o梤ed ratio of supergiant numbers, we adopted 1.0 and 1.8 as the ratio of the mixing條ength to local pressure scale height in the convection zone. We find that normal models without overshooting seems to produce too many blue supergiants while overshooting models seems to produce too many red supergiants, but neither of them can correctly predict the tendency of increasing the B/R ratios with increasing the metal abundance observed in many stellar systems. This result seems to indicate that the overshooting from the convective core is strong in extremely metal梡oor stars and fades gradually away with the increase of the metal abundance. With a proper combination of model parameters we have constructed a series of stellar models with a1.0 that give theoretical B/R ratios in better agreement with the observations, and these models have been used to calculate the period條uminosity relation of the RSG long梡eriod variables. We have compared the theoretical P桳 relations with observed long梡eriod variables in the LMC, M33 and our Milky Way. The observed LPVs are in good agreementwith the P桳 relations of the fundamental mode for the LMC and M33, but the LPVs in the M~I seems to have shorter periods and more likely to be the first overtone pulsators. We have found that the period條uminosity relations under different metal I icity show a tendency of decreasing the luminosity and increasing the period with the increase of the metal abundance, 3 and the correction of the luminosity at a given period is ~Mb0I 0.836 lgZ.