Kepler detection of a new extreme planetary system orbiting the subdwarf-B pulsator KIC10001893

摘要

KIC10001893 is one out of 19 subdwarf-B (sdB) pulsators observed by theKepler spacecraft in its primary mission. In addition to tens of pulsationfrequencies in the g-mode domain, its Fourier spectrum shows three weak peaksat very low frequencies, which is too low to be explained in terms of g modes.The most convincing explanation is that we are seeing the orbital modulation ofthree Earth-size planets (or planetary remnants) in very tight orbits, whichare illuminated by the strong stellar radiation. The orbital periods areP1=5.273, P2=7.807, and P3=19.48 hours, and the period ratios P2/P1=1.481 andP3/P2=2.495 are very close to the 3:2 and 5:2 resonances, respectively. One ofthe main pulsation modes of the star at 210.68 {\mu}Hz corresponds to the thirdharmonic of the orbital frequency of the inner planet, suggesting that we see,for the first time in an sdB star, g-mode pulsations tidally excited by aplanetary companion. The extreme planetary system that emerges from the Keplerdata is very similar to the recent discovery of two Earth-size planets orbitingthe sdB pulsator KIC05807616 (Charpinet et al. 2011a).