Speaker: Henry Prager

Title: Updates on the Atmospheric Properties of Pulsating Asymptotic Giant Branch Stars

Abstract:

Asymptotic Giant Branch (AGB) stars are a type of long-period variable star, marking the end-of-life stage for stars on the scale of the Sun. These stars experience opacity driven pulsations, driving the repeated contraction and expansion of the star. In the stellar atmosphere, the pulsations interact with mineral dusts, resulting in the mass-loss phenomenon, where material is shed from the star before becoming a white dwarf.

These stars pulsate in spherical modes, most frequently the fundamental and first-overtone modes. Observations show that stars pulsating in both modes lose mass, yet mass loss in the fundamental mode appears to be far more effective. Using the atmospheric pulsation code written by George Bowen, my collaborators and I have been investigating this phenomenon in stars pulsating in these modes. Results from these models show that the difference is a consequence of the acoustic properties of the stellar atmosphere. In these models, shock waves generated by stars in the fundamental mode are able to efficiently propagate through the stellar atmosphere and maintain structure for tens of stellar radii, while stars pulsating in the first-overtone or higher modes are incapable of the same.