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Title: Characterising the Atmospheres of the HR8799 Planets with HST/WFC3
Author: Abhijith Rajan, Travis S. Barman, Remi Soummer, J. Brendan Hagan, Jennifer L. Patience, Laurent Pueyo, Elodie Choquet, Quinn Konopacky, Bruce Macintosh, Christian Marois

We present results from a Hubble Space Telescope (HST) program characterising the atmospheres of the outer two planets, in the HR8799 system. The images were taken over 15 orbits in three near-infrared medium-band filters - F098M, F127M and F139M - using the Wide Field Camera 3. One of the three filters is sensitive to water absorption band inaccessible from ground-based observations, providing a unique probe of the thermal emission from the atmospheres of these young giant planets. The observations were taken at 30 different spacecraft rolls to enable angular differential imaging, and the full data set was analysed with the Karhunen-Loeve Image Projection (KLIP) routine, an advanced image processing algorithm adapted to work with HST data. To achieve the required high contrast at sub arcsecond resolution, we utilised the pointing accuracy of HST in combination with an improved pipeline designed to combine the dithered, angular differential imaging data with an algorithm designed to both improve the image resolution and accurately measure the photometry. The results include F127M (J) detections of the outer planets, HR8799 b and c and the first detection of HR8799 b in the water-band (F139M) filter. The F127M photometry for HR8799 c agrees well with fitted atmospheric models resolving a long standing difficulty to model the near-IR flux for the planet consistently

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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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HR 8799c
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Distant planetary system is a super-sized solar system

A team of astronomers, including Quinn Konopacky of the Dunlap Institute for Astronomy & Astrophysics, University of Toronto, has made the most detailed examination yet of the atmosphere of a Jupiter-like planet beyond our Solar System.
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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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HR 8799 Planets
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Title: Masses, Radii, and Cloud Properties of the HR 8799 Planets
Authors: Mark S. Marley, Didier Saumon, Michael Cushing, Andrew S. Ackerman, Jonathan J. Fortney, Richard Freedman

The near-infrared colours of the planets directly imaged around the A star HR 8799 are much redder than most field brown dwarfs of the same effective temperature. Previous theoretical studies of these objects have concluded that the atmospheres of planets b, c, and d are unusually cloudy or have unusual cloud properties. Most studies have also found that the inferred radii of some or all of the planets disagree with expectations of standard giant planet evolution models. Here we compare the available data to the predictions of our own set of atmospheric and evolution models that have been extensively tested against observations of field L and T dwarfs, including the reddest L dwarfs. Unlike almost all previous studies we require mutually consistent choices for effective temperature, gravity, cloud properties, and planetary radius. This procedure thus yields plausible values for the masses, effective temperatures, and cloud properties of all three planets. We find that the cloud properties of the HR 8799 planets are not unusual but rather follow previously recognized trends, including a gravity dependence on the temperature of the L to T spectral transition--some reasons for which we discuss. We find the inferred mass of planet b is highly sensitive to whether or not we include the H and K band spectrum in our analysis. Solutions for planets c and d are consistent with the generally accepted constraints on the age of the primary star and orbital dynamics. We also confirm that, like in L and T dwarfs and solar system giant planets, non-equilibrium chemistry driven by atmospheric mixing is also important for these objects. Given the preponderance of data suggesting that the L to T spectral type transition is gravity dependent, we present an exploratory evolution calculation that accounts for this effect. Finally we recompute the bolometric luminosity of all three planets.

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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: LBT observations of the HR 8799 planetary system: First detection of HR8799e in H band
Authors: S. Esposito, D. Mesa, A. Skemer, C. Arcidiacono, R.U. Claudi, S. Desidera, R. Gratton, F. Mannucci, F. Marzari, E. Masciadri, L. Close, P. Hinz, C. Kulesa, D. McCarthy, J. Males, G. Agapito, J. Argomedo, K. Boutsia, R. Briguglio, G. Brusa, L. Busoni, G. Cresci, L. Fini, A. Fontana, J.C. Guerra, J.M. Hill, D. Miller, D. Paris, A. Puglisi, F. Quiros-Pacheco, A. Riccardi, P. Stefanini, V. Testa, M. Xompero, C. Woodward

We have performed H and Ks band observations of the planetary system around HR 8799 using the new AO system at the Large Binocular Telescope and the PISCES Camera. The excellent instrument performance (Strehl ratios up to 80% in H band) enabled detection the inner planet HR8799e in the H band for the first time. The H and Ks magnitudes of HR8799e are similar to those of planets c and d, with planet e slightly brighter. Therefore, HR8799e is likely slightly more massive than c and d. We also explored possible orbital configurations and their orbital stability. We confirm that the orbits of planets b, c and e are consistent with being circular and coplanar; planet d should have either an orbital eccentricity of about 0.1 or be non-coplanar with respect to b and c. Planet e can not be in circular and coplanar orbit in a 4:2:1 mean motion resonances with c and d, while coplanar and circular orbits are allowed for a 5:2 resonance. The analysis of dynamical stability shows that the system is highly unstable or chaotic when planetary masses of about 5 MJup for b and 7 MJup for the other planets are adopted. Significant regions of dynamical stability for timescales of tens of Myr are found when adopting planetary masses of about 3.5, 5, 5, and 5 Mjup for HR 8799 b, c, d, and e respectively. These masses are below the current estimates based on the stellar age (30 Myr) and theoretical models of substellar objects.

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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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Title: Orbital Motion of HR 8799 b,c, d using Hubble Space Telescope data from 1998: Constraints on Inclination, Eccentricity and Stability
Authors: Remi Soummer, J. Brendan Hagan, Laurent Pueyo, Adrien Thormann, Abhijith Rajan, Christian Marois

HR 8799 is currently the only multiple-planet system that has been detected with direct imaging, with four giant planets orbiting at large separations from this young late A star. Orbital motion provides insight into the stability, and possible formation mechanisms of this planetary system. Dynamical studies can also provide constraints on the planets' masses, which help calibrate evolutionary models. Yet, measuring the orbital motion is a very difficult task because the long-period orbits (50-500 yr) require long time baselines and high-precision astrometry. This paper studies the three planets HR 8799b, c and d in the archival data set of HR 8799 obtained with the HST NICMOS coronagraph in 1998. The detection of all three planets is made possible by a careful optimisation of the LOCI algorithm. This work confirms previous astrometry for planet b, and presents new detections and astrometry for c and d. These HST images provide a ten-year baseline with the discovery images from 2008, and therefore offer a unique opportunity to constrain their orbital motion now. Recent dynamical studies of this system show the existence of a few possible stable solutions involving mean motion resonances, where the interaction between c and d plays a major role. We study the compatibility of a few of these stable scenarios (1d:1c, 1d:2c, or 1d:2c:4d) with the new astrometric data from HST. In the hypothesis of a 1d:2c:4b mean motion resonance our best orbit fit is close to the stable solution previously identified for a three-planet system, and involves low eccentricity for planet d (ed = 0.10) and moderate inclination of the system (i = 28.0 deg), assuming a coplanar system, circular orbits for b and c, and exact resonance with integer period ratios. Under these assumptions, we can place strong constraints on the inclination of the system (27.3 - 31.4 deg) and on the eccentricity for d ed < 0.46.

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Astronomers Find Elusive Planets in Decade-Old Hubble Data

In a painstaking re-analysis of Hubble Space Telescope images from 1998, astronomers have found visual evidence for two extrasolar planets that went undetected back then.
Finding these hidden gems in the Hubble archive gives astronomers an invaluable time machine for comparing much earlier planet orbital motion data to more recent observations. It also demonstrates a novel approach for planet hunting in archival Hubble data.

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