Colloquium on 29 May 2014
Pulsational properties of the B-type supergiants


Title: Pulsational properties of the B-type supergiants
Speaker: Jakub Ostrowski
Date: Thursday, 29 May 2014
Time: 11:00 - 12:00
Venue: SAAO Auditorium


The unexpected discovery of pulsational frequencies in the light variations of the blue supergiant HD 163899 (B2 Ib/II) has prompted a few groups to re-analysis of pulsational stability in models after Terminal Age Main Sequence (TAMS). The star has become a prototype of a new class of pulsating variables coined Slowly Pulsating B-type supergiants (SPBsg). Previously, it was believed that pulsations (especially g-modes) cannot be present beyond Main Sequence (MS) due to a very strong radiative damping in the helium core. The presence of g-mode pulsations in B-type post main sequence stars has been explained by a partial reflection of some modes at an intermediate convective zone related to the hydrogen shell burning or at chemical gradient zone surrounding the radiative core. However, these two interpretations are based on the assumption that HD 163899 is before helium core ignition, i.e., in the phase of hydrogen shell burning. This assumption does not have to be necessarily adequate because the blue loop can reach temperatures of early B spectral types. Using MESA evolution code and a non-adiabatic pulsation code, I investigate and compare SPBsg models before and after He core ignition. The new instability areas and comparison of pulsational properties of models on both evolution phases will be presented. I will also discuss prospects for mode identification in such stars. Analysis of SPBsg stars can be of great value for understanding poorly known details of physics of massive stars on the later stages of evolution, such as parameters of convective zones or influence of various parameters on the emergence and shape of the blue loops.

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