* Astronomy

Title: Detection of Carbon Monoxide and Water Absorption Lines in an Exoplanet Atmosphere
Authors: Quinn M. Konopacky, Travis S. Barman, Bruce A. Macintosh, Christian Marois

Determining the atmospheric structure and chemical composition of an exoplanet remains a formidable goal. Fortunately, advancements in the study of exoplanets and their atmospheres have come in the form of direct imaging - spatially resolving the planet from its parent star - which enables high-resolution spectroscopy of self-luminous planets in Jovian-like orbits. Here, we present a spectrum with numerous, well-resolved, molecular lines from both water and carbon monoxide from a massive planet orbiting less than 40 AU from the star HR 8799. These data reveal the planet's chemical composition, atmospheric structure, and surface gravity, confirming that it is indeed a young planet. The spectral lines suggest an atmospheric carbon-to-oxygen ratio greater than the host star's, providing hints about the planet's formation.

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Title: The CHARA Array Angular Diameter of HR 8799 Favors Planetary Masses for Its Imaged Companions
Authors: Ellyn K. Baines, Russel J. White, Daniel Huber, Jeremy Jones, Tabetha Boyajian, Harold A. McAlister, Theo A. ten Brummelaar, Judit Sturmann, Laszlo Sturmann, Nils H. Turner, P. J. Goldfinger, Christopher D. Farrington, Adric R. Riedel, Michael Ireland, Kaspar von Braun, Stephen T. Ridgway

HR 8799 is an hF0 mA5 gamma Doradus, lambda Bootis, Vega-type star best known for hosting four directly imaged candidate planetary companions. Using the CHARA Array interferometer, we measure HR 8799's limb-darkened angular diameter to be 0.342 ± 0.008 mas; this is the smallest interferometrically measured stellar diameter to date, with an error of only 2%. By combining our measurement with the star's parallax and photometry from the literature, we greatly improve upon previous estimates of its fundamental parameters, including stellar radius (1.44 ± 0.06 solar radii), effective temperature (7193 ± 87 K, consistent with F0), luminosity (5.05 ± 0.29 solar luminosity), and the extent of the habitable zone (1.62 AU to 3.32 AU). These improved stellar properties permit much more precise comparisons with stellar evolutionary models, from which a mass and age can be determined, once the metallicity of the star is known. Considering the observational properties of other lambda Bootis stars and the indirect evidence for youth of HR 8799, we argue that the internal abundance, and what we refer to as the effective abundance, is most likely near-solar. Finally, using the Yonsei-Yale evolutionary models with uniformly scaled solar-like abundances, we estimate HR 8799's mass and age considering two possibilities: 1.516 +0.038/-0.024 solar masses and 33 +7/-13 Gyr if the star is contracting toward the zero age main-sequence or 1.513 +0.023/-0.024 solar masses and 90 +381/-50 Gyr if it is expanding from it. This improved estimate of HR 8799's age with realistic uncertainties provides the best constraints to date on the masses of its orbiting companions, and strongly suggests they are indeed planets. They nevertheless all appear to orbit well outside the habitable zone of this young star.

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Title: First Light LBT AO Images of HR 8799 bcde at 1.65 and 3.3 Microns: New Discrepancies between Young Planets and Old Brown Dwarfs
Authors: Andrew J. Skemer, Philip M. Hinz, Simone Esposito, Adam Burrows, Jarron Leisenring, Michael Skrutskie, Silvano Desidera, Dino Mesa, Carmelo Arcidiacono, Filippo Mannucci, Timothy J. Rodigas, Laird Close, Don McCarthy, Craig Kulesa, Guido Agapito, Daniel Apai, Javier Argomedo, Vanessa Bailey, Konstantina Boutsia, Runa Briguglio, Guido Brusa, Lorenzo Busoni, Riccardo Claudi, Joshua Eisner, Luca Fini, Katherine B. Follette, Peter Garnavich, Raffaele Gratton, Juan Carlos Guerra, John M. Hill, William F. Hoffmann, Terry Jones, Megan Krejny, Jared Males, Elena Masciadri, Michael R. Meyer, Douglas L. Miller, Katie Morzinski, Matthew Nelson, Enrico Pinna, Alfio Puglisi, Sascha P. Quanz, Fernando Quiros-Pacheco, Armando Riccardi, Paolo Stefanini, Vidhya Vaitheeswaran, John C. Wilson, Marco Xompero

As the only directly imaged multiple planet system, HR 8799 provides a unique opportunity to study the physical properties of several planets in parallel. In this paper, we image all four of the HR 8799 planets at H-band and 3.3 microns with the new LBT adaptive optics system, PISCES, and LBTI/LMIRCam. Our images offer an unprecedented view of the system, allowing us to obtain H and 3.3$ micron photometry of the innermost planet (for the first time) and put strong upper-limits on the presence of a hypothetical fifth companion. We find that all four planets are unexpectedly bright at 3.3 microns compared to the equilibrium chemistry models used for field brown dwarfs, which predict that planets should be faint at 3.3 microns due to CH4 opacity. We attempt to model the planets with thick-cloudy, non-equilibrium chemistry atmospheres, but find that removing CH4 to fit the 3.3 micron photometry increases the predicted L' (3.8 microns) flux enough that it is inconsistent with observations. In an effort to fit the SED of the HR 8799 planets, we construct mixtures of cloudy atmospheres, which are intended to represent planets covered by clouds of varying opacity. In this scenario, regions with low opacity look hot and bright, while regions with high opacity look faint, similar to the patchy cloud structures on Jupiter and L/T transition brown-dwarfs. Our mixed cloud models reproduce all of the available data, but self-consistent models are still necessary to demonstrate their viability.

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Title: High-Mass, Four-Planet Models for HR 8799: Constraining the Orbital Inclination and Age of the System
Authors: Jeffrey J. Sudol, Nader Haghighipour

Debates regarding the age and inclination of the planetary system orbiting the star HR 8799 and the recent release of additional astrometric data prompted us to carry out a series of dynamical simulations of this system at several different inclinations for planetary masses of 7-10-10-10 Jupiter masses. We find the longest system lifetimes are less than ~5 Myr at inclinations of 0° and 13°, and ~41, ~46, and ~31 Myr at 18°, 23°, and 30°, respectively. Given such short dynamical lifetimes, and considering the location of the system on the age-luminosity diagram for low-mass objects, the most reasonable conclusion is that the planetary masses are less than 7-10-10-10 Jupiter masses and the system is quite young. We do find, however, one model at i=30° that remains stable for ~155 Myr, permitting an older system with higher mass planets. Although the chi-squared statistics for this model are marginal, at best, we are not inclined to reject it because of the potential for systematic differences between the astrometric data obtained with different instruments. Furthermore, we constrained the orbital elements of the planets to their astrometric coordinates from one particular instrument at a single epoch, and we assumed the orbits of the planets to be coplanar. The interesting trend to note from our simulations is that the coordinates for planet e in the most stable models tend to be closer to the star than the observed coordinates. We present the details of our models and discuss the implications of the results.

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