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We present a new analysis of the rapidly oscillating Ap (roAp) star, 2MASSJ$19400781-4420093$ (J1940; $V=13.1$). The star was discovered using SuperWASPbroadband photometry to have a frequency of 176.39 d$^{-1}$ (2041.55 $\mu$Hz;$P = 8.2$ min; Holdsworth et al. 2014a) and is shown here to have apeak-to-peak amplitude of 34 mmag. J1940 has been observed during three seasonsat the South African Astronomical Observatory, and has been the target of aWhole Earth Telescope campaign. The observations reveal that J1940 pulsates ina distorted quadrupole mode with unusual pulsational phase variations. A highersignal-to-noise ratio spectrum has been obtained since J1940's firstannouncement, which allows us to classify the star as A7 Vp Eu(Cr). Theobserving campaigns presented here reveal no pulsations other than theinitially detected frequency. We model the pulsation in J1940 and conclude thatthe pulsation is distorted by a magnetic field of strength $1.5$ kG. Adifference in the times of rotational maximum light and pulsation maximumsuggests a significant offset between the spots and pulsation axis, as can beseen in roAp stars.

Whole Earth Telescope discovery of a strongly distorted quadrupole pulsation in the largest amplitude rapidly oscillating Ap star