In the solar system, the planets' compositions vary with orbital distance, with rocky planets in close orbits and lower-density gas giants in wider orbits. The detection of close-in giant planets around other stars was the first clue that this pattern is not universal and that planets' orbits can change substantially after their formation. Here, we report another violation of the orbit-composition pattern: two planets orbiting the same star with orbital distances differing by only 10% and densities differing by a factor of 8. One planet is likely a rocky "super-Earth," whereas the other is more akin to Neptune. These planets are 20 times more closely spaced and have a larger density contrast than any adjacent pair of planets in the solar system.

We have studied solar-like oscillations in ∼ 800 red-giant stars using Kepler long-cadence photometry. The sample includes stars ranging in evolution from the lower part of the red-giant branch to the Helium main sequence. We investigate the relation between the large frequency separation (∆ν) and the frequency of maximum power (ν max ) and show that it is different for red giants than for mainsequence stars, which is consistent with evolutionary models and scaling relations. The distributions of ν max and ∆ν are in qualitative agreement with a simple stellar population model of the Kepler field, including the first evidence for a secondary clump population characterized by M 2 M ⊙ and ν max ≃ 40−110 µHz. We measured the small frequency separations δν 02 and δν 01 in over 400 stars and δν 03 in over 40. We present C-D diagrams for l = 1, 2 and 3 and show that the frequency separation ratios δν 02 /∆ν and δν 01 /∆ν have opposite trends as a function of ∆ν. The data show a narrowing of the l = 1 ridge towards lower ν max , in agreement with models predicting more efficient mode trapping in stars with higher luminosity. We investigate the offset ǫ in the asymptotic relation and find a clear correlation with ∆ν, demonstrating that it is related to fundamental stellar parameters. Finally, we present the first amplitude-ν max relation for Kepler red giants. We observe a lack of low-amplitude stars for ν max 110 µHz and find that, for a given ν max between 40 − 110 µHz, stars with lower ∆ν (and consequently higher mass) tend to show lower amplitudes than stars with higher ∆ν.

We have analyzed solar-like oscillations in ∼1700 stars observed by the Kepler Mission, spanning from the main-sequence to the red clump. Using evolutionary models, we test asteroseismic scaling relations for the frequency of maximum power (ν max ), the large frequency separation (∆ν) and oscillation amplitudes. We show that the difference of the ∆ν-ν max relation for unevolved and evolved stars can be explained by different distributions in effective temperature and stellar mass, in agreement with what is expected from scaling relations. For oscillation amplitudes, we show that neither (L/M ) s scaling nor the revised scaling relation by Kjeldsen & Bedding (2011) is accurate for red-giant stars, and demonstrate that a revised scaling relation with a separate luminosity-mass dependence can be used to calculate amplitudes from the main-sequence to red-giants to a precision of ∼25%. The residuals show an offset particularly for unevolved stars, suggesting that an additional physical dependency is necessary to fully reproduce the observed amplitudes. We investigate correlations between amplitudes and stellar activity, and find evidence that the effect of amplitude suppression is most pronounced for subgiant stars. Finally, we test the location of the cool edge of the instability strip in the Hertzsprung-Russell diagram using solar-like oscillations and find the detections in the hottest stars compatible with a domain of hybrid stochastically excited and opacity driven pulsation.

The granulation pattern that we observe on the surface of the Sun is due to hot plasma from the interior rising to the photosphere where it cools down, and descends back into the interior at the edges of granules. This is the visible manifestation of convection taking place in the outer part of the solar convection zone. Because red giants have deeper convection zones and more extended atmospheres than the Sun, we cannot a priori assume that granulation in red giants is a scaled version of solar granulation. Until now, neither observations nor 1D analytical convection models could put constraints on granulation in red giants.However, thanks to asteroseismology, this study can now be performed. The resulting parameters yield physical information about the granulation. We analyze ∼ 1000 red giants that have been observed by Kepler during 13 months. We fit the power spectra with Harvey-like profiles to retrieve the characteristics of the granulation (time scale τ gran and power P gran ). We also introduce a new time scale, τ eff , which takes into account that different slopes are used in the Harvey functions. We search for a correlation between these parameters and the global acoustic-mode parameter (the position of maximum power, ν max ) as well as with stellar parameters (mass, radius, surface gravity (log g) and effective temperature (T eff )). We show that τ eff ∝ ν −0.89 max and P gran ∝ ν −1.90 max , which is consistent with the theoretical predictions. We find that the granulation time scales of stars that belong to the red clump have similar values while the time scales of stars in the red-giant branch are spread in a wider range. Finally, we show that realistic 3D simulations of the surface convection in stars, spanning the (T eff , log g)-range of our sample of red giants, match the Kepler observations well in terms of trends.

Measurements of 500 Sun-like stars show that their properties differ from those predicted by stellar population models.