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Astron. Astrophys. 359, 646-650 (2000)


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Long-term optical spectral observations of the Be/X-ray binary LSI +61o303: evidence of H[FORMULA] 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

1 Purple Mountain Observatory, Nanjing 210008, P.R. China, National Astronomical Observatories, Chinese Academy of Sciences
2 Astronomical Institute "Anton Pannekoek", University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
3 Yunnan Observatory, P.O. Box 110, Kunming 650011, P.R. China, National Astronomical Observatories, Chinese Academy of Sciences

Received 14 March 2000 / Accepted 11 May 2000

Abstract

We present the optical spectra of the periodic radio star LSI +61o303 with intermediate dispersion. The H[FORMULA] 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[FORMULA] 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[FORMULA] 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[FORMULA] emission line all occurred at radio phases around 0.8. It is interesting to note that the H[FORMULA] emission line in 1995 October showed unusual variation at radio phases around 0.6, where the decrease of the H[FORMULA] 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[FORMULA] 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

Send offprint requests to: Q.Z. Liu (qzliu@astro.uva.nl)

© European Southern Observatory (ESO) 2000

Online publication: July 7, 2000

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