Astron. Astrophys. 332, 958-968 (1998)

Period changes of Scuti stars and stellar evolution

M. Breger ¹ and A.A. Pamyatnykh <sup>1, 2, 3

1</sup> Astronomisches Institut der Universität Wien, Türkenschanzstr. 17, A-1180 Wien, Austria (breger@astro.univie.ac.at)
² Copernicus Astronomical Center, Bartycka 18, PL-00-716 Warsaw, Poland
³ Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya Str. 48, 109017 Moscow, Russia

Received 28 November 1997 / Accepted 15 January 1998

Abstract

Period changes of Scuti stars have been collected or redetermined from the available observations and are compared with values computed from evolutionary models with and without convective core overshooting.

For the radial pulsators of Pop. I, the observations indicate (1/P) dP/dt values around 10^-7 year^-1 with equal distribution between period increases and decreases. The evolutionary models, on the other hand, predict that the vast majority should show increasing periods. This increase should be a factor of about ten times smaller than observed. For nonradial Scuti pulsators of Pop. I, the discrepancies are even larger. The behavior suggests that for these relatively unevolved stars the rate of evolution cannot be deduced from the period changes.

The period changes of most Pop. II Scuti (SX Phe) stars are characterized by sudden jumps of the order of 10^-6. However, at least one star, BL Cam, shows a large, continuous period increase. The variety of observed behavior also seems to exclude an evolutionary origin of the changes.

Model calculations show that the evolutionary period changes of pre-MS Scuti stars are a factor of 10 to 100 larger than those of MS stars. Detailed studies of selected pre-MS Scuti stars are suggested.

Key words: ffi Sct stars: oscillations stars: evolution stars: pre main sequence stars: individual: AI Vel

Send offprint requests to: M. Breger

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Contents

• 1. Introduction
• 2. Predicted period changes due to stellar evolution
  • 2.1. Standard evolutionary models and their oscillations
  • 2.2. Evolutionary period changes
  • 2.3. Effects of stellar rotation and convective overshooting
  • 2.4. Period changes during fast phases of post-MS evolution
• 3. Observed period changes
• 4. Period changes among Pop. I Scuti stars
  • 4.1. On non-evolutionary period changes
• 5. Observed period changes in SX Phe stars
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: March 30, 1998
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