# Summary of K2 Program GO12107

Title: Probing the Internal Mixing Processes and Angular Momentum Transport in Pulsating B-type Stars on the Main Sequence

PI: Papics, Peter I (Instituut voor Sterrenkunde)
CoIs: Buysschaert, Bram D; Moravveji, Ehsan; Aerts, Conny Clara

The lifetime of massive stars is strongly influenced by internal mixing processes such as core overshooting, diffusion, and rotation. Our knowledge of these processes is very limited, and this lack of understanding results in large uncertainties on current stellar structure and evolution models of massive stars. As these models are important cornerstones for several fields of modern astrophysics (e.g., chemical enrichment of galaxies, stellar life cycles and their effects on star and planetary system formation, dynamics of stellar clusers, etc.), these shortcomings need to be resolved.

Asteroseismology is one of the few tools that allow us to study the interiors of stars by the interpretation of their pulsation signal. The last decade brought an immense revolution to the field thanks to the succes of space telescopes such as CoRoT and Kepler, and thanks to vast improvements of asteroseismological techniques. The frequency spectra of the pulsating beta Cep and slowly pulsating B (SPB) stars are strongly influenced by the mentioned mixing processes (e.g., Miglio et al. 2008, MNRAS, 386, 1487), which makes them ideal asteroseismic probes.

Even in the era of space-based telescopes, observations of OB stars are a rarity, not only because of their relatively low number compared to Solar-like and KM dwarves, but also because they are preferably avoided by missions driven by exoplanet detections. While the nominal Kepler mission delivered a revolution in stellar physics for Solar-like stars and red giants, it only added a few stars to the still less than two dozens of OB dwarves where in-depth studies managed to put at least some constraints on the extent of the overshoot region around the core, or on the internal rotation profile (Aerts 2015, IAUS, 307, 154A). Even more striking is that there is only one star where a full actual seismic modelling was carried out based on gravity modes, resulting in stringent constraints on the core overshoot (Papics et al. 2014, A&A, 570, A8) and the diffusive mixing (Moravveji et al. 2015, A&A, 580, A27), culminating in an inversion of the internal rotation profile (Triana et al. 2015, ApJ, 810, 16). The few available observational studies have demonstrated that the richness of variable behaviour among these stars is so large that the details in their internal physics must be different. This means that we need to map the whole extent of the instability strip with in-depth seismic modelling efforts to find the connection between the fundamental parameters and the internal mixing properties of these stars. This is the only way we can calibrate the stellar structure and evolution models of massive stars.

We propose the observation of 35 potential B-type pulsators, that have been selected based on spectral type and brightness. We propose stars where we can conduct simultaneous and follow-up observations with the high-resolution HERMES spectrograph and the 3-channel MAIA CCD camera installed on the 1.2 meter Mercator Telescope on La Palma (operated by the host institute of the PI).

Our methodology is as follows: we do frequency analysis on the detrended K2 data, then we attempt mode identification using period- and frequency-spacing patterns, or  if this is not possible  using multicolour photometry or time-resolved high-resolution high signal-to-noise spectroscopy. This is followed by forward modelling of the zonal modes. We iterate over theoretical frequency sets calculated using different input physics to fine-tune the equilibrium models until we reach the best fit. This will result in a new generation of stellar structure models. There might be stars that are found to be non pulsating, but these non-detections coupled with precise spectroscopy will be also very useful to validate the current excitation calculations, especially since at the moment the predicted instability strips on the HRD are still very undersampled in terms of observational data.

# Targets requested by this program that have been observed (1)
EPIC ID, RA (J2000) [deg], Dec (J2000) [deg], magnitude, Investigation IDs
246320565, 353.792487, -2.651429, 11.673, GO12127_LC|GO12052_LC|GO12107_LC