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Kepler-16b
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NASA's Kepler Discovery Confirms First Planet Orbiting Two Stars

The existence of a world with a double sunset, as portrayed in the film Star Wars more than 30 years ago, is now scientific fact. NASA's Kepler mission has made the first unambiguous detection of a circumbinary planet -- a planet orbiting two stars -- 200 light-years from Earth.
Unlike Star Wars' Tatooine, the planet is cold, gaseous and not thought to harbor life, but its discovery demonstrates the diversity of planets in our galaxy. Previous research has hinted at the existence of circumbinary planets, but clear confirmation proved elusive. Kepler detected such a planet, known as Kepler-16b, by observing transits, where the brightness of a parent star dims from the planet crossing in front of it.

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V4046 Sagittarii
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Title: The close classical T Tauri binary V4046 Sgr: Complex magnetic fields & distributed mass accretion
Authors: J.F. Donati, S.G. Gregory, T. Montmerle, A. Maggio, C. Argiroffi, G. Sacco, G. Hussain, J. Kastner, S.H.P. Alencar, M. Audard, J. Bouvier, F. Damiani, M. Gudel, D. Huenemoerder, G.A. Wade

We report here the first results of a multi-wavelength campaign focussing on magnetospheric accretion processes within the close binary system V4046 Sgr, hosting two partly-convective classical T Tauri stars of masses ~0.9 Msun and age ~12 Myr. In this paper, we present time-resolved spectropolarimetric observations collected in 2009 September with ESPaDOnS at the Canada-France-Hawaii Telescope (CFHT) and covering a full span of 7d or ~2.5 orbital/rotational cycles of V4046 Sgr. Small circularly polarised Zeeman signatures are detected in the photospheric absorption lines but not in the accretion-powered emission lines of V4046 Sgr, thereby demonstrating that both system components host large-scale magnetic fields weaker and more complex than those of younger, fully-convective cTTSs of only a few Myr and similar masses.
Applying our tomographic imaging tools to the collected data set, we reconstruct maps of the large-scale magnetic field, photospheric brightness and accretion-powered emission at the surfaces of both stars of V4046 Sgr. We find that these fields include significant toroidal components, and that their poloidal components are mostly non-axisymmetric with a dipolar component of 50-100G strongly tilted with respect to the rotation axis; given the similarity with fields of partly-convective main-sequence stars of similar masses and rotation periods, we conclude that these fields are most likely generated by dynamo processes. We also find that both stars in the system show cool spots close to the pole and extended regions of low-contrast, accretion-powered emission; it suggests that mass accretion is likely distributed rather than confined in well defined high-contrast accretion spots, in agreement with the derived magnetic field complexity.

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Young binary star system V4046 Sagittarii
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Giant planets, comets and Pluto-like bodies may form around binary star systems, not just single stars, a new study suggests.
The evidence comes via a rotating, molecular disk found orbiting the young binary star system V4046 Sagittarii with the Submillimeter Array's radio telescope system atop Mauna Kea, Hawaii. This finding was announced last week by a team of astronomers at the 214th meeting of the American Astronomical Society in Pasadena, California.
The discovery suggests that other binary systems could host as-yet undetected planets.

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V4046 Sagittarii
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Astronomers are announcing today that a sequence of images collected with the Smithsonian's Submillimeter Array (SMA) clearly reveals the presence of a rotating molecular disk orbiting the young binary star system V4046 Sagittarii. The SMA images provide an unusually vivid snapshot of the process of formation of giant planets, comets, and Pluto-like bodies. The results also confirm that such objects may just as easily form around double stars as around single stars like our Sun.
These findings are being presented by UCLA graduate student David Rodriguez in a press conference at the American Astronomical Society meeting in Pasadena, California.

"We believe that V4046 Sagittarii provides one of the clearest examples yet discovered of a Keplerian, planet-forming disk orbiting a young star system. This particular system is made that much more remarkable by the fact that it consists of a pair of solar-mass stars that are approximately 12 million years old and are separated by a mere 5 solar diameters" - Co-author David Wilner of the Harvard-Smithsonian Centre for Astrophysics

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RE: Double sun sunset
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Life on a planet ruled by two suns might be a little complicated. Two sunrises, two sunsets. Twice the radiation field.
In a paper published in the December 2008 issue of Astronomy and Astrophysics, astronomer Joel Kastner and his team suggest that planets may easily form around certain types of twin (or "binary") star systems. A disk of molecules discovered orbiting a pair of twin young suns in the constellation Sagittarius strongly suggests that many such binary systems also host planets.

"We think the molecular gas orbiting these two stars almost literally represents 'smoking gun' evidence of recent or possibly ongoing 'giant' (Jupiter-like) planet formation around the binary star system" - Kastner, professor at Rochester Institute of Technology's Chester F. Carlson Center for Imaging Science.

Kastner used the 30-meter radiotelescope operated by the Institut de Radio Astronomie Millimetrique (IRAM) to study radio molecular spectra emitted from the vicinity of the two stars in a binary system called V4046 Sgr, which lies about 210 light-years away from our solar system. (V4046 Sgr is the 4046th brightest variable-brightness star in the constellation Sagittarius.) The scientists found "in large abundance" raw materials for planet formation around the nearby stars, including circumstellar carbon monoxide and hydrogen cyanide, in the noxious molecular gas cloud.
The young stars, approximately 10 million years old, are close in proximity to each other - only 10 solar diameters apart - and orbit each other once every 2.5 days.

Source Rochester Institute of Technology

V4046 Sagittarii
Position(2000): RA = 18 14 10.4660, Dec =  -32 47 34.496

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Title:   Planet Formation in Binary Stars: The case of Gamma Cephei
Authors: Wilhelm Kley (1), Richard Nelson (2) ((1) University of Tuebingen, (2) University of London)

Over 30 planetary systems have been discovered to reside in binary stars. For small separations gravitational perturbation of the secondary star has a strong influence on the planet formation process. It truncates the protoplanetary disk, may shortens its lifetime, and stirs up the embedded planetesimals. Due to its small semi-major axis (18.5 AU) and large eccentricity (e=0.35) the binary gamma Cephei represents a particularly challenging example. In the present study we model the orbital evolution and growth of embedded protoplanetary cores of about 30 earth masses in the putative protoplanetary disk surrounding the primary star in the gamma Cep system. We assume coplanarity of the disk, binary and planet and perform two-dimensional hydrodynamic simulations of embedded cores in a protoplanetary disk. The presence of the eccentric secondary star perturbs the disk periodically and generates strong spiral arms at periapse which propagate toward the disk centre. The disk also becomes slightly eccentric (with e_d = 0.1-0.15), and displays a slow retrograde precession in the inertial frame. For all initial separations (2.5 to 3.5 AU) we find inward migration of the cores. For initial semi-major axes (a_p \gsim 2.7), we find a strong increase in the planetary eccentricity despite the presence of inward migration. Only cores which are initially far from the disk outer edge have a bounded orbital eccentricity which converges, roughly to the value of the planet observed in the gamma Cep system. We have shown that under the condition protoplanetary cores can form at around 2.5 AU, it is possible to evolve and grow such a core to form a planet with final outcome similar to that observed.

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Title: Orbital Stability of Planets in Binary Systems: A New Look at Old Results
Authors: J. Eberle, M. Cúntz, Z. E. Musielak


About half of all known stellar systems with Sun-like stars consist of two or more stars, significantly affecting the orbital stability of any planet in these systems. This observational evidence has prompted a large array of theoretical research, including the derivation of mathematically stringent criteria for the orbital stability of planets in stellar binary systems, valid for the "coplanar circular restricted three-body problem". In the following, we use these criteria to explore the validity of results from previous theoretical studies.

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Planets in Binaries
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Title: Habitability of Planets in Binaries
Authors: Nader Haghighipour

A survey of currently known extrasolar planets indicates that close to 20% of their hosting stars are members of binary systems. While the majority of these binaries are wide (i.e., with separations between 250 and 6500 AU), the detection of Jovian-type planets in the three binaries of Gamma Cephei (separation of 18.5 AU), GL 86 (separation of 21 AU), and HD 41004 (separation of 23 AU) have brought to the forefront questions on the formation of giant planets and the possibility of the existence of smaller bodies in moderately close binary star systems. This paper discusses the late stage of the formation of habitable planets in binary systems that host Jovian-type bodies, and reviews the effects of the binary companion on the formation of Earth-like planets in the system's habitable zone. The results of a large survey of the parameter-space of binary-planetary systems in search of regions where habitable planets can form and have long-term stable orbits are also presented.
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RE: Double sun sunset
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The double sunset that Luke Skywalker gazed upon in the film Star Wars might not be a fantasy.
Astronomers using NASA's Spitzer Space Telescope have observed that planetary systems -- dusty disks of asteroids, comets, and possibly planets -- are at least as abundant in twin-star systems as they are in those, like our own, with only one star. Since more than half of all stars are twins, or binaries, the finding suggests the universe is packed with planets that have two suns. Sunsets on some of those worlds would resemble the ones on Luke Skywalker's planet, Tatooine, where two fiery balls dip below the horizon one by one.

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Double sun sunset no longer science fiction
An international research team from University of Jena (Germany), Nagoya University, and Harvard-Smithsonian Centre (USA) has recently obtained the first direct images of the second "Sun" around a planet-hosting star, gam Cep, using the Subaru telescope and the telescope at Calar Alto (Spain). The determination of physical parameters of the system, such as masses of the two stars and a minimum mass of the exo-planet, has been significantly improved based on the direct detection.

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