Very peculiar wind from BD+53 2790, the optical counterpart to 4U 2206+54

TL;DR

This paper investigates the peculiar wind and spectral features of BD+53 2790, an optical counterpart to a high-mass X-ray binary, revealing unusual wind properties and possible classification as a He-rich star.

Contribution

It provides new insights into the star's wind characteristics and spectral peculiarities, challenging the typical classification of similar stars.

Findings

Detected a slow, dense wind unusual for an O9.5V star

Identified persistent asymmetry in H-alpha line profiles

Suggested the star may be He-rich with an atypical circumstellar environment

Abstract

BD+53 2790, an O9.5Vp star, is the optical counterpart to the HMXRB 4U 2206+54. This system was classified initially as a BeX, but observational evidence soon stressed the need to revise this classification. The permanent asymmetry in the H-alpha line profiles (in contrast with the cyclic variations shown by Be stars), the variations in the profile of this line in time scales of hours (while time scales from weeks to months are expected in Be stars), and the lack of correlation between IR observables and H-alpha line parameters, strongly suggest that, while BD+53 2790 contains a circunstellar disc, it is not like the one present in Be stars. Furthermore, there is evidence of overabundance of He in BD+53 2790. Together with the presence of an anomalous wind, found through UV spectroscopy, the possibility to link this star with the group of He rich stars is open. We will discuss the work done with IUE data from BD+53 2790 and the unexpected finding of a slow and dense wind, very rare for an O9.5V star.