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We present an analysis of the first Kepler K2 mission observations of arapidly oscillating Ap (roAp) star, HD 24355 ($V=9.65$). The star wasdiscovered in SuperWASP broadband photometry with a frequency of 224.31d$^{-1}$, (2596.18 $\mu$Hz; $P = 6.4$ min) and an amplitude of 1.51 mmag, withlater spectroscopic analysis of low-resolution spectra showing HD 24355 to bean A5 Vp SrEu star. The high precision K2 data allow us to identify 13rotationally split sidelobes to the main pulsation frequency of HD 24355. Thisnumber of sidelobes combined with an unusual rotational phase variation showthis star to be the most distorted quadrupole roAp pulsator yet observed. Inmodelling this star, we are able to reproduce well the amplitude modulation ofthe pulsation, and find a close match to the unusual phase variations. We showthis star to have a pulsation frequency higher than the critical cut-offfrequency. This is currently the only roAp star observed with the Keplerspacecraft in Short Cadence mode that has a photometric amplitude detectablefrom the ground, thus allowing comparison between the mmag amplitudeground-based targets and the $\mu$mag spaced-based discoveries. No furtherpulsation modes are identified in the K2 data, showing this star to be asingle-mode pulsator.

HD 24355 observed by the Kepler K2 mission: A rapidly oscillating Ap star pulsating in a distorted quadrupole mode