Kepler-68: Three Planets, One with a Density between That of Earth and Ice Giants
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چکیده
NASA’s Kepler Mission has revealed two transiting planets orbiting Kepler-68. Follow-up Doppler measurements have established the mass of the innermost planet and revealed a third jovian-mass planet orbiting beyond the two transiting planets. Kepler-68b, in a 5.4 day orbit, has MP = 8.3 +2.2 −2.4 M⊕, RP = 2.31 +0.06 −0.09 R⊕, and ρP = 3.32 +0.86 −0.98 g cm , giving Kepler-68b a density intermediate between that of the ice giants and Earth. Kepler-68c is Earth-sized with a radius, RP = 0.953 +0.037 −0.042 R⊕ and transits on a 9.6 day orbit; validation of Kepler-68c posed unique challenges. Kepler-68d has an orbital period of 580 ± 15 days and minimum mass of MP sin i= 0.947 ± 0.035MJ . Power spectra of the Kepler photometry at 1-minute cadence exhibit a rich and strong set of asteroseismic pulsation modes enabling detailed analysis of the stellar interior. Spectroscopy of the star coupled with asteroseismic modeling of the multiple pulsation modes yield precise measurements of stellar properties, notably Teff = 5793 ± 74 K, M⋆ = 1.079 ± 0.051 M⊙, R⋆ = 1.243 ± 0.019 R⊙, and ρ⋆ = 0.7903±0.0054 g cm , all measured with fractional uncertainties of only a few percent. Models of Kepler-68b suggest it is likely composed of rock and water, or has a H and He envelope to yield its density ∼3 g cm. Subject headings: planetary systems — stars: fundamental parameters — stars: individual (Kepler-68, KIC 11295426, 2MASS J19240775+4902249)
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تاریخ انتشار 2013