Astronomy and Astrophysics, volume 300, 200-206 (1995/8-1)
A star at the frontier between p- and g-modes: ιHerculis.
MATHIAS P. and WAELKENS C.
Abstract (from CDS):
Six nights have been devoted to an intensive spectroscopic study (410 spectra in the Hδ domain) of the star ιHer. 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 0.8km/s, slightly varying. The short time 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, ιHer lies in the HR diagram at the frontier where p- and g-modes are excited due to the metal opacity bump mechanism.