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