Evidence of H alpha periodicities in LS I+61303

TL;DR

This study detects the 26.5-day radio period in H-alpha emission of LS I+61303 and observes long-term variations suggesting changes in the Be star's circumstellar disk density and mass loss rate.

Contribution

First detection of the 26.5-day radio period in H-alpha spectra of LS I+61303, linking radio and optical variability and revealing dense circumstellar disk characteristics.

Findings

26.5-day radio period detected in H-alpha emission

Long-term 1600-day modulation in spectral features

Circumstellar disk identified as among the densest of Be-stars

Abstract

We present the results of analyzing H$\alpha$ spectra of the radio emitting X-ray binary LS I+61303. For the first time, the same 26.5 d radio period is clearly detected in the H$\alpha$ emission line. Moreover, the equivalent width and the peak separation of the H$\alpha$ emission line seem also to vary over a time scale of 1600 days. This points towards the $\sim4$ yr modulation, detected in the radio outburst amplitude, being probably a result of variations in the mass loss rate of the Be star and/or density variability in the circumstellar disk. In addition, the dependence of the peak separation from the equivalent width informs us that the LS I+61303 circumstellar disk is among the densest of Be-stars.