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

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1. Introduction

The investigation of the pulsational behavior of [FORMULA] Scuti stars within the instability strip has motivated several surveys and statistical studies during the last decades (Breger 1969, 1970, 1972a,b, Baglin et al. 1973, Slovak 1978, Horan et al. 1979, Antonello et al. 1981). Recently, the topic has been revisited in the light of the new results obtained by the Hipparcos satellite (Liu et al. 1997). Nevertheless, only a few aspects of the problem look settled now. Among the ideas generally accepted, one is that early theoretical studies (Chevalier 1971) might be correct in suggesting that all normal stars of Population I composition within the instability strip should be variable. The fact that only about 30-50 percent of these objects are detected as variables at the present time might be explained by the current detection threshold (approximately 0.01 mag) of available surveys.

Antonello et al.(1981,1983) made a statistical study of the amplitude and other parameters of [FORMULA] Scuti stars. They identified a correlation between the amplitude, period and luminosity of low amplitude [FORMULA] Scuti stars, then they indicated that this relation is not sufficient to distinguish between variable and nonvariable stars, and conclude that at the present no parameter generally observed is sufficient to allow this distinction (Antonello et al. 1981, 1983).

Another point that is generally accepted is that it is possible to classify [FORMULA] Scuti stars as low-amplitude pulsators (a few 0.01 mag or lower) and large amplitude pulsators (0.1 mag or higher), these two groups corresponding respectively to stars on the main sequence and more evolved stars in the hydrogen shell-burning stage.

Considering that the relation for the amplitude of [FORMULA] Scuti variables found by Antonello et al. is not unique (Antonello et al. 1981), for the purpose of deciding which parameters have a strong real relation with the amplitude, we made a statistical analysis of the [FORMULA] Scuti variables located in several open clusters. In our analysis, we combine observations of light curves, [FORMULA] index, and V sini from the literature as listed in Table 1 with improved distance moduli from Hipparcos data or new ground-based parallax observations. Here we report some of the results.


[TABLE]

Table 1. [FORMULA] Scuti variables selected from Open Clusters. Different columns represent absolute magnitude, oscillation amplitude, [FORMULA], [FORMULA], weight according to the length of time series, age, spectra class, HD number (or SAO number), cluster name and references.
Ref.
1. Rodriguez et al. (1994); 2. Crawford et al. (1974); 3. Mermilliod (1981); 4. Slovak (1978); 5. Gatewood et al. (1990); 6. Breger (1972b); 7. Gatewood et al. (1995); 8. Breger (1969); 9. Horan (1979); 10. Gatewood et al. (1992); 11. Mermilliod et al. (1997); 12. Breger (1973); 13. Breger (1970); 14. Rolland et al. (1990); 15. Jackisch (1972); 16. Breger et al. (1993); 17 Paparo et al. (1990); 18 Breger (1975).


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© European Southern Observatory (ESO) 1999

Online publication: March 18, 1999
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