The slowly pulsating B-star 18 Peg: A testbed for upper main sequence stellar evolution

TL;DR

This paper discusses how the star 18 Peg can serve as a crucial observational benchmark to better understand the width of the upper main sequence in stellar evolution models, especially regarding convective overshooting.

Contribution

It identifies 18 Peg as a valuable testbed for constraining the upper main sequence width through asteroseismic and spectroscopic analysis.

Findings

18 Peg is a highly evolved slowly pulsating B-star.

It is part of a long-period binary system.

Further detailed observations are needed for comprehensive analysis.

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. Based on a photometric and preliminary asteroseismic analysis, we show that the mid B-type giant 18 Peg is one of the most evolved members of the rare class of slowly pulsating B-stars and, thus, bears tremendous potential to derive a tight lower limit for the width of the upper main sequence. In addition, 18 Peg turns out to be part of a single-lined spectroscopic binary system with an eccentric orbit that is greater than 6 years. Further spectroscopic and photometric monitoring and a sophisticated asteroseismic investigation are required to exploit the full potential of this star as a benchmark object for stellar evolution theory.