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Astron. Astrophys. 344, L41-L44 (1999)

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4. Conclusions

We report here some results of a statistical study of [FORMULA] Scuti stars from 5 open clusters. These results show a trend suggesting an increase of oscillation amplitude with absolute magnitude. Comparing the present results to those of Antonello et al. (1981), except for two low-amplitude stars of greater luminosity, the low-amplitude stars in the sample of Antonello et al. appear to show a trend similar to that found in the present paper, with a similar y-intercept but a different slope and much more scatter. Our results suggest, when the observational accuracy is improved enough, the cool border of [FORMULA] Scuti instability on the main sequence will move towards the cool direction. No correlation is noticed between the oscillation amplitude and the effective temperature.

It is generally accepted that all main sequence normal stars in the instability strip might be pulsating, but amplitudes of most of them are too low to be detected when considering the detection threshold of current available surveys. The statistical studies show that the nonvariable normal stars and [FORMULA] Scuti stars are distributed randomly in the instability strip (Breger 1979, Baglin et al. 1973). But the correlation suggested by the present analysis hardly fits the general assumption that all stars in the instability strip are variables. Only if most of the stars in the instability strip are really constant can our result be in agreement with the statistical results. [FORMULA] Scuti stars are so close to pulsational stability that small physical differences from star to star may be very important and push the star to stability. So we think [FORMULA] Scuti variables and nonvariables coexist on the instability strip. This idea is in agreement with the suggestion of Leung (1970) that [FORMULA] Scuti variables lie in two well defined boxes containing short and long-period pulsators respectively, and that most nonvariables would be outside the boxes so they show constant brightness. Certainly, how to define the boxes is an important topic that needs further study.

Further observational work and refinement in the way to estimate oscillation amplitudes are necessary to confirm these results.

If confirmed, this trend might improve our understanding of the pulsational behavior of normal stars in the instability strip.

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© European Southern Observatory (ESO) 1999

Online publication: March 18, 1999