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HR 8799 Planetary System
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Title: Observational Constraints on Companions inside of 10 AU in the HR 8799 Planetary System
Authors: Sasha Hinkley (1,2), John M. Carpenter (1), Michael J. Ireland (3), Adam L. Kraus (4) ((1) Caltech (2) Sagan Fellow, (3) Sydney University, (4) Hubble Fellow, Institute for Astronomy, University of Hawaii)

We report the results of Keck L'-band non-redundant aperture masking of HR 8799, a system with four confirmed planetary mass companions at projected orbital separations of 14 to 68 AU. We use these observations to place constraints on the presence of planets and brown dwarfs at projected orbital separations inside of 10 AU---separations out of reach to more conventional direct imaging methods. No companions were detected at better than 99% confidence between orbital separations of 0.8 to 10 AU. Assuming an age of 30 Myr and adopting the Baraffe models, we place upper limits to planetary mass companions of 80, 60, and 11 Jupiter Masses at projected orbital separations of 0.8, 1, and 3-10 AU respectively. Our constraints on massive companions to HR 8799 will help clarify ongoing studies of the orbital stability of this multi-planet system, and may illuminate future work dedicated to understanding the dust-free hole interior to ~6 AU.

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RE: HR 8799
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Quartet of giant planets puzzles astronomers

The discovery of a fourth giant world around the star HR 8799 is straining the two leading theories of how planets form.
Planets are thought to coalesce from a dusty disc around a young star. One model, called core accretion, says that giant planets form when the dust gathers into a rocky core, which then draws in gas to form a massive atmosphere. Another, called disc instability, says that these planets collapse suddenly from sections of the disc.
HR 8799's four planets, each five to 13 times Jupiter's mass, are too far apart to be explained easily by either model, say Christian Marois of the Herzberg Institute of Astrophysics in Victoria, British Columbia, Canada, and colleagues.

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Exoplanets cast doubt on astronomical theories

Astronomers who study how planets form are scratching their heads after two studies have shown that all is not as theory would predict in the world of other-worldly worlds.
The papers, both published online in Nature today, concern planets outside our own Solar System. The existence of one confounds current ideas on planet formation, whereas measurements of the other's atmosphere throw into doubt theories about atmospheric composition and its relationship to a planet's interior.

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HR8799e
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New pictures show fourth planet in giant version of our solar system

Astronomers have discovered a fourth giant planet, joining three others that, in 2008, were the subject of the first-ever pictures of a planetary system orbiting another star other than our sun.
The solar system, discovered by a team from Lawrence Livermore National Laboratory and the National Research Council of Canada (NRC) Herzberg Institute of Astrophysics with collaborators at University of California, Los Angeles and Lowell Observatory, orbits around a dusty young star named HR8799, which is 129 light years away. All four planets are roughly five to seven times the mass of Jupiter.

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RE: HR 8799
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Title: Images of a fourth planet orbiting HR 8799
Authors: C. Marois, B. Zuckerman, Q. M. Konopacky, B. Macintosh, T. Barman

High-contrast near-infrared imaging of the nearby star HR 8799 has shown three giant planets. Such images were possible due to the wide orbits (> 25 AU) and youth (< 100 Myr) of the imaged planets, which are still hot and bright as they radiate away gravitational energy acquired during their formation. A major area of contention in the extrasolar planet community is whether outer planets (> 10 AU) more massive than Jupiter form via one-step gravitational instabilities or, rather, via a two-step process involving accretion of a core followed by accumulation of a massive outer envelope composed primarily of hydrogen and helium. Here we report the presence of a fourth planet, interior to and about the same mass as the other three. The system, with this additional planet, represents a challenge for current planet formation models as none of them can explain the in situ formation of all four planets. With its four young giant planets and known cold/warm debris belts, the HR 8799 planetary system is a unique laboratory to study the formation and evolution of giant planets at wide > 10 AU separations.

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HR8799b, c, d
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Small, Ground-Based Telescope Images Three Exoplanets

Astronomers have snapped a picture of three planets orbiting a star beyond our own using a modest-sized telescope on the ground. The surprising feat was accomplished by a team at NASA's Jet Propulsion Laboratory in Pasadena, Calif., using a small portion of the Palomar Observatory's Hale Telescope, north of San Diego.
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The three planets, called HR8799b, c and d, are thought to be gas giants like Jupiter, but more massive. They orbit their host star at roughly 24, 38 and 68 times the distance between our Earth and sun, respectively (Jupiter resides at about 5 times the Earth-sun distance).
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RE: HR 8799
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Title: Age determination of the HR8799 planetary system using asteroseismology
Authors: A. Moya, P. J. Amado, D. Barrado, A. García Hernández, M. Aberasturi, B. Montesinos, F. Aceituno

Discovery of the first planetary system by direct imaging around HR8799 has made the age determination of the host star a very important task. This determination is the key to derive accurate masses of the planets and to study the dynamical stability of the system. The age of this star has been estimated using different procedures. In this work we show that some of these procedures have problems and large uncertainties, and the real age of this star is still unknown, needing more observational constraints. Therefore, we have developed a comprehensive modelling of HR8799, and taking advantage of its gamma Doradus-type pulsations, we have estimated the age of the star using asteroseismology. The accuracy in the age determination depends on the rotation velocity of the star, and therefore an accurate value of the inclination angle is required to solve the problem. Nevertheless, we find that the age estimate for this star previously published in the literature ([30,160] Myr) is unlikely, and a more accurate value might be closer to the Gyr. This determination has deep implications on the value of the mass of the objects orbiting HR8799. An age around ~ 1 Gyr implies that these objects are brown dwarfs.

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Title: The planetary system host HR 8799: On its lambda Bootis nature
Authors: A. Moya, P. J. Amado, D. Barrado, A. García Hernández, M. Aberasturi, B. Montesinos, F. Aceituno

HR 8799 is a \lambda Bootis, \gamma Doradus star hosting a planetary system and a debris disk with two rings. This makes this system a very interesting target for asteroseismic studies. This work is devoted to the determination of the internal metallicity of this star, linked with its \lambda Bootis nature (i.e., solar surface abundances of light elements, and subsolar surface abundances of heavy elements), taking advantage of its \gamma Doradus pulsations. This is the most accurate way to obtain this information, and this is the first time such a study is performed for a planetary-system-host star. We have used the equilibrium code CESAM and the non-adiabatic pulsational code GraCo. We have applied the Frequency Ratio Method (FRM) and the Time Dependent Convection theory (TDC) to estimate the mode identification, the Brunt-Vaisala frequency integral and the mode instability, making the selection of the possible models. When the non-seismological constraints (i.e its position in the HR diagram) are used, the solar abundance models are discarded. This result contradicts one of the main hypothesis for explaining the \lambda Bootis nature, namely the accretion/diffusion of gas by a star with solar abundance. Therefore, according to these results, a revision of this hypothesis is needed. The inclusion of accurate internal chemical mixing processes seems to be necessary to explain the peculiar abundances observed in the surface of stars with internal subsolar metallicities. The use of the asteroseismological constraints, like those provided by the FRM or the instability analysis, provides a very accurate determination of the physical characteristics of HR 8799. However, a dependence of the results on the inclination angle i still remains. The determination of this angle, more accurate multicolour photometric observations, and high resolution spectroscopy can definitively fix the mass and metallicity of this star.

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Après la première observation directe d'un système planétaire extrasolaire en 2008, des chercheurs viennent de réaliser la première observation du spectre lumineux de l'une des trois planètes de ce système.
Le système planétaire en question, HR 8799, se trouve dans la constellation de Pégase, à 130 années-lumière de la Terre. Deux chercheurs du Département de physique de l'Université de Montréal, René Doyon et David Lafrenière, ainsi qu'un diplômé du même département, Christian Marois, avaient participé à cette découverte spectaculaire. Les trois planètes qui gravitent autour de l'étoile sont très massives, soit de 7 à 10 fois la masse de Jupiter. Le système s'est formé il y a de 30 à 50 millions d'années, ce qui est très jeune en comparaison des 4,5 milliards d'années du Soleil.

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HR 8799 c
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Title: Spatially resolved spectroscopy of the exoplanet HR 8799 c
Authors: M. Janson, C. Bergfors, M. Goto, W. Brandner, D. Lafreniere

HR 8799 is a multi-planet system detected in direct imaging, with three companions known so far. Here, we present spatially resolved VLT/NACO 3.88--4.10 micron spectroscopy of the middle planet, HR 8799 c, which has an estimated mass of ~10 Mjup, temperature of ~1100 K and projected separation of 38 AU. The spectrum shows some differences in the continuum from existing theoretical models, particularly longwards of 4 microns, implying that detailed cloud structure or non-equilibrium conditions may play an important role in the physics of young exoplanetary atmospheres.

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