Discovery of very low amplitude 9-minute multiperiodic pulsations in the magnetic Ap star HD 75445
arXiv:0812.1565 · doi:10.1051/0004-6361:200811419
Abstract
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.
5 pages, 3 figures; accepted for publication in Astronomy and Astrophysics
References in corpus (8)
- Evolutionary state of magnetic chemically peculiar stars
- Rare-earth elements in the atmosphere of the magnetic chemically peculiar star HD 144897. New classification of the Nd III spectrum
- Pulsation tomography of rapidly oscillating Ap stars. Resolving the third dimension in peculiar pulsating stellar atmospheres
- Isotopic anomaly and stratification of Ca in magnetic Ap stars
- Pulsations in the atmosphere of the rapidly oscillating Ap star 10 Aquilae
- Line profile variations in rapidly oscillating Ap stars: resolution of the enigma
- The discovery of high-amplitude 10.9-minute oscillations in the cool magnetic Ap star HD 115226
- The Paschen-Back effect in the Li I 6708 A line and the presence of lithium in cool magnetic Ap stars