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TOPIC: Extrasolar Planets


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RE: Extrasolar Planets
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Exoplanet systems around other stars are surprisingly flat compared with our own. The discovery means that the solar system must have had a far more colourful history than many of its counterparts and is forcing astronomers to rethink their ideas about the way planetary systems form.
The new findings come from NASA's Kepler spacecraft, which has spent the past two years looking for the telltale dimming of nearby stars as planets pass in front of them. So far it has looked at 155,000 stars and found 1000 with signs of planets.

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Title: Spin-orbit inclinations of the exoplanetary systems HAT-P-8, HAT-P-9, HAT-P-16 and HAT-P-23
Authors: Claire Moutou, Rodrigo F. Diaz, Stephane Udry, Guillaume Hebrard, Francois Bouchy, Alexandre Santerne, David Ehrenreich, Luc Arnold, Isabelle Boisse, Xavier Bonfils, Xavier Delfosse, Anne Eggenberger, Thierry Forveille, Anne-Marie Lagrange, Christophe Lovis, Patrick Martinez, Francesco Pepe, Christian Perrier, Didier Queloz, Nuno C. Santos, Damien Segransan, Dominique Toublanc, Jean-Pierre Troncin, Michael Vanhuysse, Alfred Vidal-Madjar

We report the measurement of the spin-orbit angle of the extra-solar planets HAT-P-8 b, HAT-P-9 b, HAT-P-16 b and HAT-P-23 b, thanks to spectroscopic observations performed at the Observatoire de Haute-Provence with the SOPHIE spectrograph on the 1.93-m telescope. Radial velocity measurements of the Rossiter-McLaughlin effect show the detection of an apparent prograde, aligned orbit for all systems. The projected spin-orbit angles are found to be lambda=-17 deg (+9.2,-11.5), -16 deg (8), -10 deg (16), +15 deg (22) for HAT-P-8, HAT-P-9, HAT-P-16 and HAT-P-23 respectively, with corresponding projected rotational velocities of 14.5 (0.8), 12.5 (1.8), 3.9 (0.8), and 7.8 (1.6) km/s. These new results increase to 37 the number of accurately measured spin-orbit angles in transiting extrasolar systems. We conclude by drawing a tentative picture of the global behaviour of orbital alignment, involving the complexity and diversity of possible mechanisms.

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'Free-floating' planets found with no star in sight

Japanese astronomers claim to have found free-floating "planets" which do not seem to orbit a star.
Writing in Nature, they say they have found 10 Jupiter-sized objects which they could not connect to any solar system. They also believe such objects could be as common as stars are throughout the Milky Way.

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Title: Detecting the Signatures of Uranus and Neptune
Authors: Stephen R. Kane

With more than 15 years since the first radial velocity discovery of a planet orbiting a Sun-like star, the time baseline for radial velocity surveys is now extending out beyond the orbit of Jupiter analogs. The sensitivity to exoplanet orbital periods beyond that of Saturn orbital radii however is still beyond our reach such that very few clues regarding the prevalence of ice giants orbiting solar analogs are available to us. Here we simulate the radial velocity, transit, and photometric phase amplitude signatures of the solar system giant planets, in particular Uranus and Neptune, and assess their detectability. We scale these results for application to monitoring low-mass stars and compare the relative detection prospects with other potential methods, such as astrometry and imaging. These results quantitatively show how many of the existing techniques are suitable for the detection of ice giants beyond the snow line for late-type stars and the challenges that lie ahead for the detection true Uranus/Neptune analogues around solar-type stars.

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Title: Planet Formation In Highly Inclined Binary Systems I. Planetesimals Jump Inwards And Pile Up
Authors: Ji-Wei Xie, Matthew Payne, Philippe Thebault, Ji-Lin Zhou, Jian Ge

Most detected planet-bearing binaries are in wide orbits, for which a high inclination, i_B, between the binary orbital plane and the plane of the planetary disk around the primary is likely to be common. In this paper, we investigate the intermediate stages - from planetesimals to planetary embryos/cores - of planet formation in such highly inclined cases. Our focus is on the effects of gas drag on the planetesimals' orbital evolution, in particular on the evolution of the planetesimals' semimajor axis distribution and their mutual relative velocities. We first demonstrate that a non-evolving axisymmetric disk model is a good approximation for studying the effects of gas drag on a planetesimal in the highly inclined case (30 <i_B<150). We then find that gas drag plays a crucial role, and the results can be generally divided into two categories, i.e., the Kozai-on regime and the Kozai-off regime, depending on the specific value of i_B. For both regimes, a robust outcome over a wide range of parameters is that, planetesimals migrate/jump inwards and pile up, leading to a severely truncated and dense planetesimal disk around the primary. In this compact and dense disk, collision rates are high but relative velocities are low, providing conditions which are favourable for planetesimal growth, and potentially allow for the subsequent formation of planets.

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Dark matter could make planets habitable

Dark matter could make planets that would otherwise be hostile to life habitable, a new study suggests. It suggests that in areas rich in dark matter, particles of the stuff could collect inside free-floating planets that have no star to warm them, heating them enough to maintain liquid water on their surfaces.
No one knows what dark matter is - astronomers merely detect its gravitational pull on normal matter, which it seems to outweigh by a factor of five to one. But many researchers believe it is made of particles called WIMPs, which interact only weakly with normal matter but annihilate on contact with each other, creating a spray of energetic particles.

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Title: Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler
Authors: Andrew W. Howard, Geoffrey W. Marcy, Stephen T. Bryson, Jon M. Jenkins, Jason F. Rowe, Natalie M. Batalha, William J. Borucki, David G. Koch, Edward W. Dunham, Thomas N. Gautier III, Jeffrey Van Cleve, William D. Cochran, David W. Latham, Jack J. Lissauer, Guillermo Torres, Timothy M. Brown, Ronald L. Gilliland, Lars A. Buchhave, Douglas A. Caldwell, Jorgen Christensen-Dalsgaard, David Ciardi, Francois Fressin, Michael R. Haas, Steve B. Howell, Hans Kjeldsen, Sara Seager, Leslie Rogers, Dimitar D. Sasselov, Jason H. Steffen, Gibor S. Basri, David Charbonneau, Jessie Christiansen, Bruce Clarke, Andrea Dupree, Daniel C. Fabrycky, Debra A. Fischer, Eric B. Ford, Jonathan J. Fortney, Jill Tarter, Forrest R. Girouard, Matthew J. Holman, John Asher Johnson, Todd C. Klaus, Pavel Machalek, Althea V. Moorhead, Robert C. Morehead, Darin Ragozzine, Peter Tenenbaum, Joseph D. Twicken, Samuel N. Quinn, Howard Isaacson, Avi Shporer, Philip W. Lucas, Lucianne M. Walkowicz, William F. Welsh, Alan Boss, Edna Devore, Alan Gould, Jeffrey C. Smith, Robert L. Morris, Andrej Prsa, Timothy D. Morton et al. (17 additional authors not shown)

We report the distribution of planets as a function of planet radius (R_p), orbital period (P), and stellar effective temperature (Teff) for P < 50 day orbits around GK stars. These results are based on the 1,235 planets (formally "planet candidates") from the Kepler mission that include a nearly complete set of detected planets as small as 2 Earth radii (Re). For each of the 156,000 target stars we assess the detectability of planets as a function of R_p and P. We also correct for the geometric probability of transit, R*/a. We consider first stars within the "solar subset" having Teff = 4100-6100 K, logg = 4.0-4.9, and Kepler magnitude Kp < 15 mag. We include only those stars having noise low enough to permit detection of planets down to 2 Re. We count planets in small domains of R_p and P and divide by the included target stars to calculate planet occurrence in each domain. Occurrence of planets varies by more than three orders of magnitude and increases substantially down to the smallest radius (2 Re) and out to the longest orbital period (50 days, ~0.25 AU) in our study. For P < 50 days, the radius distribution is given by a power law, df/dlogR= k R^\alpha. This rapid increase in planet occurrence with decreasing planet size agrees with core-accretion, but disagrees with population synthesis models. We fit occurrence as a function of P to a power law model with an exponential cutoff below a critical period P_0. For smaller planets, P_0 has larger values, suggesting that the "parking distance" for migrating planets moves outward with decreasing planet size. We also measured planet occurrence over Teff = 3600-7100 K, spanning M0 to F2 dwarfs. The occurrence of 2-4 Re planets in the Kepler field increases with decreasing Teff, making these small planets seven times more abundant around cool stars than the hottest stars in our sample.

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Title: Abundances of Stars with Planets: Trends with Condensation Temperature
Authors: Simon C. Schuler, Davin Flateau, Katia Cunha, Jeremy R. King, Luan Ghezzi, Verne V. Smith

Precise abundances of 18 elements have been derived for ten stars known to host giant planets from high signal-to-noise ratio, high-resolution echelle spectroscopy. Internal uncertainties in the derived abundances are typically <=0.05 dex. The stars in our sample have all been previously shown to have abundances that correlate with the condensation temperature (T_c) of the elements in the sense of increasing abundances with increasing T_c; these trends have been interpreted as evidence that the stars may have accreted H-depleted planetary material. Our newly derived abundances also correlate positively with T_c, although slopes of linear least-square fits to the [m/H]-T_c relations for all but two stars are smaller here than in previous studies. When considering the refractory elements (T_c > 900 K) only, which may be more sensitive to planet formation processes, the sample can be separated into a group with positive slopes (four stars) and a group with flat or negative slopes (six stars). The four stars with positive slopes have very close-in giant planets (three at 0.05 AU) and slopes that fall above the general Galactic chemical evolution trend. We suggest that these stars have accreted refractory-rich planet material but not to the extent that would increase significantly the overall stellar metallicity. The flat or negative slopes of the remaining six stars are consistent with recent suggestions of a planet formation signature, although we show that the trends may be the result of Galactic chemical evolution.

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Kepler Orrery

All the multiple-planet systems discovered by Kepler as of 2/2/2011; orbits go through the entire mission (3.5 years). Hot colours to Cool colours (Red to yellow to green to cyan to blue to grey) are Big planets to Smaller planets, relative to the other planets in the system.

Kepler Orrery of small systems

All the multiple-planet systems discovered by Kepler as of 2/2/2011; orbits go through quarters Q0-Q2. Hot colours to Cool colours (Red to yellow to green to cyan to blue to grey) are Big planets to Smaller planets, relative to the other planets in the system.

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Milky Way Stuffed with 50 Billion Alien Worlds

There are at least 50 billion exoplanets in our galaxy. What's more, astronomers estimate that 500 million of these alien worlds are probably sitting inside the habitable zones of their parent stars.
So how many of these exoplanets have life? Unfortunately, there's no estimate for that question.

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