Irrgang, A. ; De Cat, P ; Pigulski, A. ; Handler, G. ; Tkachenko, A. ; BRITE, team

Talk presented at "Stars and their variability observed from space - Celebrating the 5th anniversary of BRITE-Constellation", Vienna, Austria on 2019-08-20

Abstract: The predicted width of the upper main sequence in stellar evolution models depends on the empirical calibration of the convective overshooting parameter. Despite decades of discussions, its precise value is still unknown and further observational constraints are required to gauge it. In 2016, Irrgang et al. discovered that the mid B-type subgiant 18 Peg is one of the most evolved members of the rare class of slowly pulsating B-stars and, thus, bears some potential to derive a tight lower limit for the width of the upper main sequence. Here, we report on new photometric and spectroscopic analyses based on follow-up observations obtained with the BRITE-Heweliusz satellite and the Hermes spectrograph, which, among others, led to a revised oscillation frequency as well as to an updated radial-velocity curve of this single-lined spectroscopic binary system.