Keplerdetection of a new extreme planetary system orbiting the subdwarf-B pulsator KIC 10001893

Abstract

KIC 10001893 is one out of 19 subdwarf-B (sdB) pulsators observed by the Kepler spacecraft in its primary mission. In addition to tens of pulsation frequencies in the g-mode domain, its Fourier spectrum shows three weak peaks at 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 of three Earth-size planets (or planetary remnants) in very tight orbits, which are illuminated by the strong stellar radiation. The orbital periods are P 1 = 5.273, P 2 = 7.807, and P 3 = 19.48 h, and the period ratios P 2 /P 1 = 1.481 and P 3 /P 2 = 2.495 are very close to the 3:2 and 5:2 resonances, respectively. One of the main pulsation modes of the star at 210.68 µHz corresponds to the third harmonic 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 a planetary companion. The extreme planetary system that emerges from the Kepler data is very similar to the recent discovery of two Earth-size planets orbiting the sdB pulsator KIC 05807616 (Charpinet et al. 2011a).

KELT-20b: A Giant Planet with a Period of P ∼ 3.5 days Transiting the V ∼ 7.6 Early A Star HD 185603

“…A few additional companions to hot stars or remnants have been announced from the Kepler mission via transits, pulsation timing, or Doppler beaming (e.g., Silvotti et al 2007Silvotti et al , 2014Charpinet et al 2011;Ahlers et al 2015;Murphy et al 2016). Finally, several directly imaged planets orbiting young stars with T 7500 K eff  have been announced, 41 the three hottest of which have very large uncertainties in the masses and radii of the planets owing to the uncertain age of their parent stars, which may put them in the brown dwarf regime (Acke & van den Ancker 2006;Lafrenière et al 2011;Carson et al 2013).…”

Hydrodynamic simulations of the interaction between giant stars and planets

“…Examples are the 1.25 MJ planet (where MJ is the mass of Jupiter) orbiting 0.116 au from a horizontal branch star (Setiawan et al 2010), two Earth-sized objects orbiting a subdwarf B star at a separation of 0.0060 and 0.0076 au (Charpinet et al 2011), or three earth-sized planets orbiting a subdwarf B pulsator (Silvotti et al 2014). These planets must have been engulfed in the envelope of the giant star that became the subdwarf star today.…”

Planetary candidates around the pulsating sdB star KIC 5807616 considered doubtful

“…Since the Kepler data were carefully reduced and there are no known artefact frequencies within this region, we concluded that both planetary signature frequencies (and perhaps a couple of others) observed beyond the cut-off frequency limits are most likely of pulsation origin. The example of KIC 5807616 also has implications for other claims of extreme planetary systems around sdB stars based on similar assumptions of the strict cut-off frequency limits for the pulsating modes (Silvotti et al 2014, KIC 10001893 sdBV), which might need to be reanalysed in a similar way to how it has been done in this paper.…”