Radial velocity variations in pulsating Ap stars – III. The discovery of 16.21-min oscillations in β CrB

We present the analysis of 3 h of a rapid time series of precise stellar radial velocity (RV) measurements (σ= 4.5 m s−1) of the cool Ap star β CrB. The integrated RV measurements spanning the wavelength interval 5000–6000 Å show significant variations (false alarm probability = 10−5) with a period of 16.21 min (ν= 1028.17 μHz) and an amplitude of 3.54 ± 0.56 m s−1. The RV measured over a much narrower wavelength interval reveals one spectral feature at λ6272.0 Å pulsating with the same 16.21-min period and an amplitude of 138 ± 23 m s−1. These observations establish β CrB to be a low-amplitude rapidly oscillating Ap star.