The onset of photometric variability in red giant stars.

Details The onset of photometric variability in red giant stars. The onset of photometric variability in red giant stars.

Aug 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...324..578j&link_type=abstract

Astronomy and Astrophysics, v.324, p.578-586

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42

Stars: Late-Type, Stars: Variable: Other, Stars: Oscillations

Scientific paper

The onset of variability in red giant stars is studied from the data collected by the `Long-Term Photometry of Variables' project which operates at ESO (La Silla) since 1982. The differential nature of the observations combined with a multi-night reduction algorithm enables to study the variability of over 50 red giants with an accuracy of the order of 2 to 3 millimagnitudes on time scales ranging from days to years. All red giants with spectral types late G to early K (i.e. b-y~0.6-0.8) are stable at the level σ_y_<6millimag (where σ_y_ is the standard deviation of the Stroemgren y magnitude). Red giants with later spectral types are all variable, and it is found that the minimum variability level σ_y, min_ increases with increasing b-y, thus defining a minimum-variability boundary. The new data obtained in this paper reveal that the time scale of the associated variability increases with increasing b-y (and thus amplitude), and that the stability of this time scale improves concomitantly. More precisely, irregular variations on time scales of 5 to 10-days (and σ_y_~7millimag) characterize red giants with b-y~1.0, whereas the variations (with σ_y_~100millimag) become more regular with periods of the order of 50d for red giants with b-y~1.3. A radial-velocity jitter (of the order of 1.5km/s r.m.s.) is associated with this photometric variability, and suggests that stellar oscillations may be responsible for the observed variations.

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