FM17.1.08 — Resolving the evolutionary stage of HD163899 from its oscillation spectrum

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Aug 12th at 12:18 PM until 12:30 PM

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Author(s): Jakub Ostrowski1, Jadwiga Daszynska-Daszkiewicz1, Henryk Cugier1

Institution(s): 1. University of Wroclaw

HD 163899 is the prototype of Slowly Pulsating B-type supergiants (SPBsg), a relatively new class of pulsating variables. Despite the efforts of many groups the physical properties of this object are still poorly known. Due to the lack of good observational data it was impossible to obtain a precise determination of its basic parameters such as effective temperature and gravity. The position of the star on the Hertzsprung-Russel diagram suggested that the star is a supergiant with a mass of about 16 M. It could be in the hydrogen shell-burning phase during the first crossing towards the red giant branch or on the blue loop during core helium burning. The first option seemed to be more plausible due the pulsational properties of the object (Ostrowski & Daszynska-Daszkiewicz 2015).
The analysis of the high-resolution spectra from the HARPS spectrograph changed the situation. Our determination of the effective temperature, mass-luminosity ratio and rotational velocity highly prefers the more massive models than previously considered (M=22-25 M). Now it is also possible that the star could be on the main sequence if convective overshooting and rotation are properly included.
Using the oscillation spectrum as a gauge, we intend to determine which stage of evolution corresponds better to HD 163899. To this end we use MESA evolutionary code and the non-adiabatic code for stellar pulsations.