Volume 493, Number 3, January III 2009
|Page(s)||L45 - L48|
|Published online||22 December 2008|
Letter to the Editor
Discovery of very low amplitude 9-minute multiperiodic pulsations in the magnetic Ap star HD 75445*
Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden e-mail: email@example.com
2 Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland, UK
3 European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Casilla 19001 Santiago 19, Chile
4 Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 109017 Moscow, Russia
5 Department of Astronomy, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria
Accepted: 8 December 2008
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 γ 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-1. 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-1 and several km s-1. 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.
Key words: stars: atmospheres / stars: chemically peculiar / stars: oscillations / stars: individual: HD 75445
© ESO, 2009
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