A star at the frontier between p- and g-modes: Herculis
P. Mathias
- C. Waelkens
Received 8 December 1994; accepted 5 January 1995
Abstract:
Six nights have been devoted to an intensive spectroscopic study (410 spectra
in the Hdelta domain) of the star iota Her. Our data sampling is not suitable
to undertake a period determination, but none of the previous published
periods seem to be valid to represent the variations we observe. This is
certainly due to a multiperiodic phenomenon. Thanks to the short exposure time,
we strongly suspect a short time scale variability in addition to the longer
periods. Therefore, two time scales would be involved, one being of the order
of a day, the other being of the order of an hour, this latter having a
2K-amplitude around 0.8 km/s, slightly varying. The short tiome scale is
clearly detected at least in 5 nights, and concerns all the studied lines.
the night-to-night variations (frequency, amplitude) measured are certainly
due to the beat-modulation with the longer periods.
From the pulsation theory, the long and short time scales can respectively
be attributed to high-order g- and p-modes. Indeed, iota Her lies in the
HR diagram at the frontier where p- and g-modes are excited due to the
metal opacity bump mechanism.
Keywords:
stars: oscillations -- stars: 53 Persei : iota Her
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