The additional-mode garden of RRab stars
Laszlo Molnar (Konkoly Observatory, MTA CSFK), Áron L. Juhász (Konkoly Observatoty, MTA CSFK, Budapest; Eötvös University, Budapest), Emese Plachy (Konkoly Observatoty, MTA CSFK, Budapest), Péter Klagyivik (Konkoly Observatoty, MTA CSFK, Budapest)

Space-based photometric missions revealed a surprising abundance of millimagnitude-level additional modes in RR Lyrae stars. The modes that appear in the modulated fundamental-mode (RRab) stars can be ordered into four major categories. Period doubling, caused by the resonant ninth overtone, and the mode at ~0.6 P0 that may potentially correspond to the second overtone, are relatively abundant in these stars. In more rare cases (including RR Lyr itself), the additional modes can be identified with the first overtone, and finally some fall outside the above mentioned categories, so they are most likely non-radial modes. Here we present a census of the additional modes based on Campaigns 0 to 6 of the K2 mission, the largest sample obtained with space-based photometry so far.