Discovery of very low amplitude 9-minute multiperiodic pulsations in the magnetic Ap star HD 75445

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.

arXiv comment5 pages, 3 figures; accepted for publication in Astronomy and Astrophysics

References in corpus (10)

• 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
• Radial Velocity Variations in Pulsating Ap Stars. II. 33 Librae
• Pulsation tomography of rapidly oscillating Ap stars. Resolving the third dimension in peculiar pulsating stellar atmospheres
• Radial Velocity Variations in Pulsating Ap Stars III. The Discovery of 16.21 min Oscillations in Beta CrB
• 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

Cited by in corpus (11)

• The first evidence for multiple pulsation axes: a new roAp star in the Kepler field, KIC 10195926
• The Nainital-Cape Survey-III : A Search for Pulsational Variability in Chemically Peculiar Stars
• Discovery of the longest-period rapidly oscillating Ap star HD177765
• TESS Cycle 1 observations of roAp stars with 2-min cadence data
• The Nainital-Cape Survey-IV
• Discovery of new roAp pulsators in the UVES survey of cool magnetic Ap stars
• Time-resolved photometric and spectroscopic analysis of a luminous Ap star HD103498
• Stellar variability on time-scales of minutes: results from the first 5 years of the Rapid Temporal Survey (RATS)
• A spectroscopic analysis of the chemically peculiar star HD207561
• Asteroseismology of Pulsating Stars
• Numerical simulations of line-profile variation beyond a single-surface approximation for oscillations in roAp stars