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Register a new userOn the Scaling and Spacing of Extra-Solar Multi-Planet Systems
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We investigate whether certain extra-solar multi-planet systems simultaneously follow the scaling and spacing rules of the angular-momentum-deficit model. The masses and semi-major axes of exoplanets in ten multi-planet systems are considered. It is found that GJ 667C, HD 215152, HD 40307, and Kepler-79 systems are currently close to configurations of the angular-momentum-deficit model. In a gas-poor scenario, GJ 3293, HD 141399, and HD 34445 systems are those which had a configuration of the angular-momentum-deficit model in the past and get scattered away due to post gaseous effects. In addition, no matter in gas-free or gas-poor scenario, 55 Cnc, GJ 876, and WASP-47 systems do not follow the angular-momentum-deficit model. Therefore, our results reveal important formation histories of these multi-planet systems.
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In order to gain possible hints for planet formation from the current data of known extra-solar planets, the period-ratios and mass-ratios of adjacent planet pairs in multi-planet systems are determined. A moderate period-ratio-mass-ratio correlation is found to have a correlation coefficient r=0.5779 with 99% confidence interval (0.464, 0.672). In contrast, for non-adjacent planet pairs, the correlation coefficient is r=0.2820 with 99% confidence interval (0.133, 0.419). Our results reveal the imprint of planet-planet interactions of the adjacent planet pairs in a certain fraction of the multi-planet systems during the stage of planet formation.
We present radial-velocity measurement of eight stars observed with the HARPS Echelle spectrograph mounted on the 3.6-m telescope in La Silla (ESO, Chile). Data span more than ten years and highlight the long-term stability of the instrument. We search for potential planets orbiting HD20003, HD20781, HD21693, HD31527, HD45184, HD51608, HD134060 and HD136352 to increase the number of known planetary systems and thus better constrain exoplanet statistics. After a preliminary phase looking for signals using generalized Lomb-Scargle periodograms, we perform a careful analysis of all signals to separate emph{bona-fide} planets from spurious signals induced by stellar activity and instrumental systematics. We finally secure the detection of all planets using the efficient MCMC available on the Data and Analysis Center for Exoplanets (DACE web-platform), using model comparison whenever necessary. In total, we report the detection of twenty new super-Earth to Neptune-mass planets, with minimum masses ranging from 2 to 30 M$_{rm Earth}$, and periods ranging from 3 to 1300 days. By including CORALIE and HARPS measurements of HD20782 to the already published data, we also improve the characterization of the extremely eccentric Jupiter orbiting this host.
Recent studies claimed that planets around the same star have similar sizes and masses and regular spacings, and that planet pairs usually show ordered sizes such that the outer planet is usually the larger one. Here I show that these patterns can be largely explained by detection biases. The emph{Kepler} planet detections are set by the transit signal-to-noise ratio (S/N). For different stellar properties and orbital period values, the same S/N corresponds to different planetary sizes. This variation in the detection threshold naturally leads to apparent correlations in planet sizes and the observed size ordering. The apparently correlated spacings, measured in period ratios, between adjacent planet pairs in systems with at least three detected planets are partially due to the arbitrary upper limit that the earlier study imposed on the period ratio, and partially due to the varying stability threshold for different planets. After these detection biases are taken into account, we do not find strong evidence for the so-called intra-system uniformity or the size ordering effect. Instead, the physical properties of emph{Kepler} planets are largely independent of the properties of their siblings and the parent star. It is likely that the dynamical evolution has erased the memory of emph{Kepler} planets about their initial formation conditions. In other words, it will be difficult to infer the initial conditions from the observed properties and the architecture of emph{Kepler} planets.
ESPI has been proposed for direct imaging and spectral analysis of giant planets orbiting solar-type stars. ESPI extends the concept suggested by Nisenson and Papaliolios (2001) for a square aperture apodized telescope that has sufficient dynamic range to directly detect exo-planets. With a 1.5 M square mirror, ESPI can deliver high dynamic range imagery as close as 0.3 arcseconds to bright sources, permitting a sensitive search for exoplanets around nearby stars and a study of their characteristics in reflected light.
We report the detection of two new planets from the Anglo-Australian Planet Search. These planets orbit two stars each previously known to host one planet. The new planet orbiting HD 142 has a period of 6005pm427 days, and a minimum mass of 5.3M_Jup. HD142c is thus a new Jupiter analog: a gas-giant planet with a long period and low eccentricity (e = 0.21 pm 0.07). The second planet in the HD 159868 system has a period of 352.3pm1.3 days, and m sin i=0.73pm0.05 M_Jup. In both of these systems, including the additional planets in the fitting process significantly reduced the eccentricity of the original planet. These systems are thus examples of how multiple-planet systems can masquerade as moderately eccentric single-planet systems.
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