Characterization of the variability in the O+B eclipsing binary HD 165246

TL;DR

This study characterizes the variability of the O+B eclipsing binary HD 165246 using high-resolution spectroscopy and space photometry, revealing details about the primary star's properties, rotation, and variability mechanisms.

Contribution

It provides an updated atmospheric and binary model for HD 165246, including a detailed analysis of the primary star's microturbulence, mass, and rotational frequency, in a sparsely explored HR diagram region.

Findings

Primary star's mass is approximately 23.7 solar masses.

Rotational frequency of the primary is about 0.690 d$^{-1}$, at 40% of critical rotation.

High microturbulence level of about 13 km/s in the primary star.

Abstract

O-stars are known to experience a wide range of variability mechanisms originating at both their surface and their near-core regions. Characterization and understanding of this variability and its potential causes are integral for evolutionary calculations. We use a new extensive high-resolution spectroscopic data set to characterize the variability observed in both the spectroscopic and space-based photometric observations of the O+B eclipsing binary HD~165246. We present an updated atmospheric and binary solution for the primary component, involving a high level of microturbulence ($13_{-1.3}^{+1.0}\,$km\,s$^{-1}$) and a mass of $M_1=23.7_{-1.4}^{+1.1}$~M$_{\odot}$, placing it in a sparsely explored region of the Hertzsprung-Russell diagram. Furthermore, we deduce a rotational frequency of $0.690\pm 0.003\,$d$^{-1}$ from the combined photometric and line-profile variability, implying that the primary rotates at 40\% of its critical Keplerian rotation rate. We discuss the potential explanations for the overall variability observed in this massive binary, and discuss its evolutionary context.