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Two years of Kepler data of KIC 8054146 (delta Sct/gamma Dor hybrid) revealed349 statistically significant frequencies between 0.54 and 191.36 c/d (6.3microHz to 2.21 mHz). The 117 low frequencies cluster in specific frequencybands, but do not show the equidistant period spacings predicted for gravitymodes of successive radial order, n, and reported for at least one other hybridpulsator. The four dominant low frequencies in the 2.8 to 3.0 c/d (32 to 35microHz) range show strong amplitude variability with timescales of months andyears. These four low frequencies also determine the spacing of the higherfrequencies in and beyond the delta Sct pressure-mode frequency domain. Infact, most of the higher frequencies belong to one of three families withspacings linked to a specific dominant low frequency. In the Fourier spectrum,these family regularities show up as triplets, high-frequency sequences withabsolutely equidistant frequency spacings, side lobes (amplitude modulations)and other regularities in frequency spacings. Furthermore, within two familiesthe amplitude variations between the low and high frequencies are related. Weconclude that the low frequencies (gravity modes, rotation) and observed highfrequencies (mostly pressure modes) are physically connected. This unusualbehavior may be related to the very rapid rotation of the star: from acombination of high and low-resolution spectroscopy we determined that KIC8054146 is a very fast rotator (v sin i = 300 +/- 20 km/s) with an effectivetemperature of 7600 +/- 200 K and a surface gravity log g of 3.9 +/- 0.3.Several astrophysical ideas explaining the origin of the relationship betweenthe low and high frequencies are explored.

Relationship between low and high frequencies in Delta Scuti stars: Photometric Kepler and spectroscopic analyses of the rapid rotator KIC 8054146