Photometric and H$α$ observations of LSI+61303: detection of a $\sim$26 day V and JHK band modulation

Abstract

We present new optical and infrared photometric observations and high resolution H$α$ spectra of the periodic radio star \lsi. The optical photometric data set covers the time interval 1985-1993 and amounts to about a hundred nights. A period of $\sim$26 days is found in the V band. The infrared data also present evidence for a similar periodicity, but with higher amplitude of variation (0\rmag 2). The spectroscopic observations include 16 intermediate and high dispersion spectra of \lsi\ collected between January 1989 and February 1993. The H$α$ emission line profile and its variations are analyzed. Several emission line parameters -- among them the H$α$ EW and the width of the H$α$ red hump -- change strongly at or close to radio maximum, and may exhibit periodic variability. We also observe a significant change in the peak separation. The H$α$ profile of \lsi\ does not seem peculiar for a Be star. However, several of the observed variations of the H$α$ profile can probably be associated with the presence of the compact, secondary star.