* Astronomy

Gas-Giant Exoplanets Cling Close to Their Parent Stars

Finding extrasolar planets has become so commonplace that it seems astronomers merely have to look up and another world is discovered. However, results from Gemini Observatory's recently completed Planet-Finding Campaign - the deepest, most extensive direct imaging survey to date - show the vast outlying orbital space around many types of stars is largely devoid of gas-giant planets, which apparently tend to dwell close to their parent stars.
"It seems that gas-giant exoplanets are like clinging offspring," says Michael Liu of the University of Hawaii's Institute for Astronomy and leader of the Gemini Planet-Finding Campaign. "Most tend to shun orbital zones far from their parents. In our search, we could have found gas giants beyond orbital distances corresponding to Uranus and Neptune in our own Solar System, but we didn't find any." The Campaign was conducted at the Gemini South telescope in Chile, with funding support for the team from the National Science Foundation and NASA. The Campaign's results, Liu says, will help scientists better understand how gas-giant planets form, as the orbital distances of planets are a key signature that astronomers use to test exoplanet formation theories.
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Title: SOPHIE velocimetry of Kepler transit candidates. V. The three hot Jupiters KOI-135b, KOI-204b and KOI-203b (alias Kepler-17b)
Authors: A. S. Bonomo, G. Hébrard, A. Santerne, N. C. Santos, M. Deleuil, J. Almenara, F. Bouchy, R. F. Díaz, C. Moutou, M. Vanhuysse

We report the discovery of two new transiting hot Jupiters, KOI-135b and KOI-204b, that were previously identified as planetary candidates by Borucki et al. 2011, and, independently of the Kepler team, confirm the planetary nature of Kepler-17b, recently announced by Desert et al. 2011. Radial-velocity measurements, taken with the SOPHIE spectrograph at the OHP, and Kepler photometry (Q1 and Q2 data) were used to derive the orbital, stellar and planetary parameters. KOI-135b and KOI-204b orbit their parent stars in 3.02 and 3.25 days, respectively. They have approximately the same radius, Rp=1.20±0.06 Jupiter radii and 1.24±0.07 Jupiter radii, but different masses Mp=3.23±0.19 Jupiter masses and 1.02±0.07 Jupiter masses. As a consequence, their bulk densities differ by a factor of four, rho_p=2.33±0.36 g.cm^-3 (KOI-135b) and 0.65±0.12 g.cm-3 (KOI-204b). Our SOPHIE spectra of Kepler-17b, used both to measure the radial-velocity variations and determine the atmospheric parameters of the host star, allow us to refine the characterisation of the planetary system. In particular we found the radial-velocity semi-amplitude and the stellar mass to be respectively slightly smaller and larger than Desert et al. These two quantities, however, compensate and lead to a planetary mass fully consistent with Desert et al.: our analysis gives Mp=2.47±0.10 Jupiter masses and Rp=1.33±0.04 Jupiter radii. We found evidence for a younger age of this planetary system, t
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Binary stars behind puffy exoplanet puzzle

Many Jupiter-like exoplanets are much larger than they ought to be. Now one astronomer thinks he knows why.
Since planets usually form at the same time as stars, astronomers can tell how old and therefore how hot and puffy the gas giants should be. But many of the recently discovered gaseous exoplanets are larger than expected.
Eduardo Martin of the Institute of Astrophysics of the Canary Islands believes this is because the puffy planets formed from the gas and dust ejected when two binary stars merged. This would make the planets much younger than their hosts, which would explain their unusual heat and puffiness. He presented his findings at the American Astronomical Society meeting in Boston last week.
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