Unusual Variability among Early F-Type Stars - HD224638 and HD224945

Details Unusual Variability among Early F-Type Stars - HD224638 and HD224945 Unusual Variability among Early F-Type Stars - HD224638 and HD224945

Sep 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994mnras.270..439m&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Vol. 270, NO. 2/SEP15, P. 439, 1994

Astronomy and Astrophysics

Astronomy

36

Scientific paper

The two main-sequence early F-type stars HD 224638 and HD 224945 show light variations of an uncommon kind. We obtained about 1000 datapoints for each star on 20 nights over a period of 35 d (corresponding to 118 h of monitoring). Frequency analysis by several different techniques shows that both light curves contain two close periodic terms of about 0.8 d-1. The two terms of HD 224638 have a double-wave shape, while those of HD 224945 have a triple-wave shape. However, these terms are unable fully to account for the light variations. A similar behaviour could also be explained by single pseudo-periodic variations with a characteristic frequency of about 0.8 d-1. High-resolution spectrograms give evidence of line profile variations in HD 224638. A discussion of the characteristics of these stars, together with those of the few similar objects found in the literature, shows that they constitute a very homogeneous class whose nature is, however, still unclear. The most promising mechanisms that can explain this phenomenon are spot activity and non-radial g-mode pulsations. Both these possibilities have many consequences in the context of stellar structure and evolution. Key words: stars: activity - stars: evolution - stars: individual: HD 224638 - stars: individual: HD 224945 - stars: oscillations.

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