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Long-term optical spectral observations of the Be/X-ray binary LSI +61o303: evidence of H emission associated with the neutron star
Q.Z. Liu 1,2,
H.R. Hang 1,
G.J. Wu 3,
J. Chang 1 and
Z.X. Zhu 1
Received 14 March 2000 / Accepted 11 May 2000
We present the optical spectra of the periodic radio star LSI +61o303 with intermediate dispersion. The H emission line profile and its variation are analyzed. Variability in LSI +61o303 is observed on different timescales. During our observations the equivalent width (EW) of H line showed long-term variability that is likely to be associated with the 4-year period. We suggest that the long-term variability is connected to the intrinsic behaviour of the Be star.
The H EW changed strongly around the radio maximum, clearly displayed a maximum at phases between 0.55-0.6, and possibly both another maximum at phases around 1.0 and a minimum between radio phases 0.7-0.9. The only three spectra that showed nearly equal intensities of the two peaks of H emission line all occurred at radio phases around 0.8. It is interesting to note that the H emission line in 1995 October showed unusual variation at radio phases around 0.6, where the decrease of the H emission accompanied by the enhancement of the emission at the red wing. These short-term and periodic phenomena can be fairly explained with the X-ray induced H emission by employing the orbital solution deduced from near-infrared light curves (Marti & Paredes 1995). Thus provides some evidence for a correlation with the orbital motion of the neutron star.
Key words: stars: binaries: close stars: emission-line, Be stars: individual: LSI +61O 303 X-rays: stars
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Online publication: July 7, 2000