Studies of mass loss and outflows from giant stars

Abstract

<p>This thesis aims to provide better understanding of mass loss and outflows from asymptotic giant branch stars using the Bowen code. There are 3 projects involved in this thesis. The main project presented here is on the morphology of the outflow when disturbed by a super Jupiter size companion. There exists resonant modes between the pulsation period and orbital period. At different resonant modes, multiple spiral arms with different spiral arm periods form in the outflows. A simple formula gives the spiral arm period as a function of pulsation and orbital periods. Since the resonant modes appear in close orbits, the decay time scale and spiral arm morphology are also presented. These results may explain asymmetry in the outflows that form planetary nebulae. It also explains the origin of the spiral arm structure around some late AGB stars. A 3-D code will ultimately be need to resolve some questions unanswered by the current 1-D models. The paper on the outflow morphology has been submitted to ApJ.</p> <p>In this thesis, ongoing mass loss studies using the Bowen code are also briefly explained. I generated a large grid of models with varying mass, luminosity, metallicity, mixing length and Bowen model parameters in order to find correlations between the mass loss rate and these parameters. Since dust abundance is an important factor for mass loss, for the third project I tested dust formation in the refrigeration zone which is closer to the photosphere than normal dusty regions. In this test, I assumed that the dust temperature equals to the gas kinetic temperature which is lower than the radiative equilibrium temperature. Since dust temperature is close to the radiative temperature when the dust grain is large, this assumption brings excessive dust into the refrigeration zones. The detailed treatment of dust formation will be refined in future studies.</p>