HR 1217 is a prototypical rapidly oscillating Ap star that has presented a test to the theory of non-radial stellar pulsation. Prior observations showed a clear pattern of five modes with alternating frequency spacings of 33.3 and 34.6 μHz, with a sixth mode at a problematic spacing of 50.0 μHz (which equals 1.5 × 33.3 μHz) to the high-frequency side. Asymptotic pulsation theory allowed for a frequency spacing of 34 μHz, but Hipparcos observations rule out such a spacing. Theoretical calculations of magnetoacoustic modes in Ap stars by Cunha predicted that there should be a previously undetected mode 34 μHz higher than the main group, with a smaller spacing between it and the highest one. In this Letter, we present preliminary results from a multisite photometric campaign on the rapidly oscillating Ap star HR 1217 using the 'Whole Earth Telescope'. While a complete analysis of the data will appear in a later paper, one outstanding result from this run is the discovery of a newly detected frequency in the pulsation spectrum of this star, at the frequency predicted by Cunha.
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2002 Royal Astronomical Society. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Stars: individual: HR 1217, Stars: magnetic fields, Stars: oscillations, stars: variables: other
Kurtz, Donald W., Steven D. Kawaler, Reed L. Riddle, M. D. Reed, Margarida S. Cunha, M. Wood, N. Silvestri et al. "Discovery of the ‘missing’mode in HR 1217 by the Whole Earth Telescope." Monthly Notices of the Royal Astronomical Society 330, no. 3 (2002): L57-L61.
Monthly Notices of the Royal Astronomical Society