Discover of the "missing" mode in HR 1217 by the Whole Earth Telescope

Abstract

HR 1217 is a prototypical rapidly oscillating Ap star that has presented a test to the theory of nonradial stellar pulsation. Prior observations showed a clear pattern of five modes with alternating frequency spacings of 33.3 microHz and 34.6 microHz, with a sixth mode at a problematic spacing of 50.0 microHz (which equals 1.5 times 33.3 microHz) to the high-frequency side. Asymptotic pulsation theory allowed for a frequency spacing of 34 microHz, but Hipparcos observations rule out such a spacing. Theoretical calculations of magnetoacoustic modes in Ap stars by Cunha (2001) predicted that there should be a previously undetected mode 34 microHz higher than the main group, with a smaller spacing between it and the highest one. In this Letter, we present preliminary results from a multi-site 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 (2001).