The evolved slowly pulsating B star 18 Peg

A Irrgang ,P De Cat ,A Tkachenko

doi:10.1051/epjconf/201715205010

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. Irrgang et al. ([1]) showed that the B3 III giant 18 Peg is one of the most evolved members of the class of slowly pulsating B (SPB) 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, more than 6-year orbit. The orbital solution, in combination with the absence of additional signatures of the secondary component in the spectroscopic data and the spectral energy distribution, lead to the conclusion that all the observations of 18 Peg are fully compatible with the assumption that the secondary component is either a main-sequence star with a mass of 1-4 M ⊙ or a neutron star.

Highlights

The predicted width of the upper main sequence in stellar evolution models depends on the empirical calibration of the convective overshooting parameter
The orbital solution, in combination with the absence of additional signatures of the secondary component in the spectroscopic data and the spectral energy distribution, lead to the conclusion that all the observations of 18 Peg are fully compatible with the assumption that the secondary component is either a main-sequence star with a mass of 1-4 M or a neutron star
We organized a follow-up campaign with the Hermes spectrograph attached to the 1.2m Mercator telescope (Roque de Los Muchachos Observatory, La Palma, Canary Islands; [3]) to gather high-quality, high-resolution spectra appropriate for the fine-tuning of the orbit and for a detailed study of the main pulsation mode

Summary

Introduction

The predicted width of the upper main sequence in stellar evolution models depends on the empirical calibration of the convective overshooting parameter. Irrgang et al ([1]) showed that the B3 iii giant 18 Peg is one of the most evolved members of the class of slowly pulsating B (SPB) stars and, bears tremendous potential to derive a tight lower limit for the width of the upper main sequence.

Results

Conclusion