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Astron. Astrophys. 362, 189-198 (2000)

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6. Conclusions

  • The analysis of all the data provided by the literature allowed the computation of new binary elements, with a larger eccentricity compared to previous results.

  • By subtracting the orbital motion from the observed velocity we could study the "pure" pulsation motion. The observed maximum night-to-night variation is about 8 km s-1. However, within a night, the amplitude is much smaller.

  • One SPBs frequency is clearly established: [FORMULA] c.d-1. Another frequency is detected in Hipparcos data around [FORMULA] c.d-1. A frequency [FORMULA] c.d-1 is present in most spectroscopic data sets, but is very faint in photometric ones. Finally, a frequency [FORMULA] c.d-1 is present in only one data set (Rogerson 1984). The frequency around 1.7 c.d-1 is more doubtful since it can be a one-day alias of [FORMULA] or [FORMULA]. Obviously, other frequencies are present, but we failed in measuring them.

  • Amplitude variations are detected along the 10 years of the observations. The typical time-scale is of the order of years. This phenomenon is similar to the one reported concerning the SPB star 53 Per (Chapellier et al., 1998).

  • For the first time, the phase-lag is measured for an SPB star. It is found to be around 0.64 P for [FORMULA] Her. This represents a new constraint for theoretical models.

  • We failed in detecting the high frequencies (around 20 c.d-1) reported earlier (e.g. Paper I). New, long term observations are needed to confirm the reality of this particular behaviour. On the contrary, power is present in the [6;8] c.d-1 range in the frequency spectrum of some data sets, corresponding to [FORMULA] Cephei type variation. It seems that the short time scale has a transient nature. No convincing explanation could be given. As both [FORMULA] Cephei and SPBs typical time scales are observed, and since [FORMULA] Her is located in the HR diagram within the SPBs instability trip and close to the [FORMULA] Cephei one, we propose that it be classified as a "hybrid" star.

Considering their typical low frequencies, together with the many modes potentially excited, SPB stars are difficult to monitor. Although the star [FORMULA] Her is one of the best observed, its behaviour remains still uncertain. Is [FORMULA] Her a typical SPB star in its large time scale behaviour? If yes, very long term monitoring is needed to understand both the atmospheric motions and the internal structure of these stars.

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© European Southern Observatory (ESO) 2000

Online publication: October 30, 19100