Astronomy and Astrophysics – Astrophysics
Scientific paper
2008-12-08
Astronomy and Astrophysics
Astrophysics
5 pages, 3 figures; accepted for publication in Astronomy and Astrophysics
Scientific paper
10.1051/0004-6361:200811419
We present our discovery of pulsational radial-velocity variations in the cool Ap star HD 75445, an object spectroscopically similar to the bright, rapidly-oscillating Ap (roAp) star gamma Equ. Based on high-resolution time-series spectroscopy obtained with the HARPS spectrometer at the European Southern Observatory 3.6-m telescope, we detected oscillations in Nd II and Nd III lines with a period close to 9 min and amplitudes of 20-30 m/s. Substantial variation in the pulsational amplitude during our 3.8 h observing run reveals the presence of at least three excited non-radial modes. The detection of extremely low amplitude pulsations in HD 75445 indicates that the roAp excitation mechanism produces variability in the radial velocity amplitude of between a few tens m/s and several km/s. This supports the idea that many, if not all, cool Ap stars occupying the roAp instability strip may harbour non-radial pulsations, which currently remain undetected due to their small photometric and radial-velocity amplitudes.
Bagnulo Stefano
Kochukhov Oleg
Lo Curto Gaspare
Ryabchikova Tanya
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