Astron. Astrophys. 351, 551-553 (1999)

4. Discussion

In the scenario outlined in this note we have shown that the plasmon containing relativistic electrons and gas formed near the periastron of the secondary orbit, floats to the top of the Be star cool disk in the polar direction to acquire a sizeable velocity. The plasmon formed at the periastron may split into two bubbles and travel in the two polar directions resulting in the twin blobs observed. The plasmon then expands in the wind of the Be star and takes time to reach the situation when it becomes optically thin at radio frequencies and attain the peak of radio emission. It is well observed (see Doazan, 1982) that the density of the Be star disk, as inferred from observations, increases, reaches a maximum and then decreases. A similar inference is made from the observed sequence of x-ray flares from the Be star/X-ray source A 0538- 66 (Apparao 1993). If the relativistic electron density is proportional to the gas density in the Be star disk, as is natural to assume, then the intensity of radio emission after each subsequent periastron passage decreases in intensity as is observed (Ray et al. 1997). According to the present suggestion the orbital phase delay, which is dependent on the energy in the relativistic electrons, will increase in subsequent radio bursts as observed (Marti & Paredes 1995; Ray et al. 1997). Thus, in each episode of the 4 yr radio emission cycle,mentioned in the introduction, and which is likely associated with the cycle of emission of cool gas by the Be star, the phase delay will show increasing values in subsequent radio bursts. During the following episode of the 4 yr cycle, the peak radio phase will again start at the periastron value and will increase. This can be verified in future observations.

© European Southern Observatory (ESO) 1999

Online publication: November 3, 1999
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