Characterisation of H$\beta$ spectra from EXO 051910+3737.7 X-rays binaries

TL;DR

This study analyzes the spectral features of the Be/X-ray binary EXO 051910+3737.7, focusing on H$eta$ and H$ extalpha$ lines, revealing double-peaked emissions, V/R variations, and estimating the H$eta$ emitting region's size.

Contribution

First detailed spectroscopic analysis of EXO 051910+3737.7's Balmer lines, highlighting asymmetries and dynamic V/R variations in the circumstellar disc.

Findings

Detected persistent double-peaked Balmer emission lines.

Observed rapid V/R fluctuations within a single day.

Estimated the H$eta$ emission region radius as approximately 2.585 times the stellar radius.

Abstract

We investigate the spectral characteristics of the Be/X-ray binary system, EXO 051910+3737.7, in which Be/X-ray systems are the largest sub-class of high-mass X-ray binaries. Spectroscopic observations are taken by the Thai National Telescope (TNT) with a Medium-RESolution spectrograph (MRES) instrument for seven nights spanning from 2020 to 2021. Our primary focus is directed towards the analysis of two Balmer lines, namely H$\alpha$ and H$\beta$, given that Be stars typically exhibit emission features in at least one of these hydrogen Balmer lines during certain phases. Our observations reveal split Balmer emission lines throughout the entire duration of our monitoring. Double Gaussian profiles were employed for line fitting to characterize these lines. The presence of double peaks in the Balmer lines indicates the presence of asymmetries within the circumstellar disc. We then analyze V/R variations and the changes in H$\beta$ spectra. Our analysis of V/R variation which Violet (V) and Red (R) peak intensity components, revealed rapid fluctuations occurring within a single day, although determining the precise periodicity was constrained by instrumental limitations and the duration of observability. Furthermore, employing observed the wavelength differences ($\Delta\lambda$) in conjunction with typical Be star parameters allowed us to estimate the radius ($r_{\beta}$) of the H$\beta$ emitting envelope. The average value was calculated to be 2.585$r_*$, with a standard deviation of 0.050$r_*$.