Good Vibrations Seminars S2E3: Siemen Burssens (KU Leuven, Belgium)

October 20, 2021 | 10:00 am 11:00 am

Exploitation of a TESS OB star asteroseismic sample: instability strips and asteroseismic modelling of HD192575

Siemen Burssens (KU Leuven)

The space mission era turned asteroseismology into a tried and tested method on large scale. While Kepler has allowed us to climb the temperature scale from solar-like pulsators up to Slowly Pulsating B stars, TESS is now boosting us to even higher masses. In particular, the OB star regime (> 8M_sun), where asteroseismic calibration is direly needed. Stars in this high mass regime are born with convective cores which essentially drive their evolution, on and beyond the main sequence. Yet, the size of this convective core remains uncalibrated at different evolutionary stages due to uncertainties in the physical prescriptions of processes such as core overshooting, interior rotation and envelope mixing. In this seminar I present new results on the large OB asteroseismic sample observed with TESS. The sample is characterised by a diverse variability, including pulsations, binarity, and rotational modulation connected to spots induced by magnetic fields. In a first instance I present the diverse photometric and spectroscopic variability of these stars, and discuss their placement in theoretical instability strips computed using the stellar evolution code MESA and the stellar pulsation code GYRE. This exercise shows that many stars that are pulsating in a particular way are not predicted to do so, which points to missing physics. This includes rotation, which is important in the OB star regime, as many stars are rotating at a significant fraction of their critical rotation rate. To investigate this further, I discuss the analysis of high-mass pulsator HD192575. This early-type star (B0.5 V) shows rotation modulation and a number of frequency multiplets induced by rotation. I present a detailed spectroscopic and photometric analysis using HERMES spectroscopy and the 1-year TESS light curve. This analysis allows us to delimit the parameter space in the Hertzsprung-Russell diagram, in which we calculated a dense grid of pulsation models with varying degrees of mixing using the MESA and GYRE codes. We derived constraints on the age and mass of the star, as well as its interior rotation and mixing properties by using an estimator which includes theoretical uncertainties in the equilibrium models. These asteroseismic solutions further provide evidence of non-rigid rotation in HD192575. I conclude by discussing the further application of the method to other high-mass pulsators in our sample.

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