A Search for Wide Companions to the Extrasolar Planetary System HR 8799

The Astrophysical Journal (Impact Factor: 5.99). 04/2009; 709(1). DOI: 10.1088/0004-637X/709/1/342
Source: arXiv


The extrasolar planetary system around HR?8799 is the first multiplanet system ever imaged. It is also, by a wide margin, the highest mass system with >27 Jupiters of planetary mass past 25?AU. This is a remarkable system with no analog in any other known planetary system. In the first part of this paper, we investigated the nature of two faint objects imaged near the system. These objects are considerably fainter (H = 20.4 and 21.6?mag) and more distant (projected separations of 612 and 534?AU) than the three known planetary companions b, c, and d (68-24?AU). It is possible that these two objects could be lower mass planets (of mass ~5M
Jup and ~3M
Jup) that have been scattered to wider orbits. We make the first direct comparison of newly reduced archival Gemini adaptive optics images to archival Hubble Space Telescope/NICMOS images. With nearly a decade between these epochs, we can accurately assess the proper motion nature of each candidate companion. We find that both objects are unbound to HR?8799 and are background. We estimate that HR?8799 has no companions of H < 22 from ~5'' to 15''. Any scattered giant planets in the HR?8799 system are >600?AU or less than 3 M
Jup in mass. In the second part of this paper, we search for any sign of a "reverse parallax signature" in the astrometric residuals of HR?8799b. No such signal was found and we conclude, as expected, that HR?8799b has the same parallax as HR?8799A. In the third part of this paper, we carry out a search for wider common proper motion objects. We found one object within 1?deg2 in the Palomar Observatory Sky Survey-Digitized Sky Survey images with similar (<2?) proper motions to HR?8799 at a separation of 40. We conclude that it is not likely a bound companion to HR?8799 based on available photometry.

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    ABSTRACT: HR8799 is a nearby A-type star with a debris disk and three planetary candidates recently imaged directly. We undertake a coherent analysis of various portions of observational data on all known components of the system. The goal is to elucidate the architecture and evolutionary status of the system. We try to further constrain the age and orientation of the system, orbits and masses of the companions, as well as the location of dust. From the high luminosity of debris dust and dynamical constraints, we argue for a rather young system's age of <50Myr. The system must be seen nearly, but not exactly, pole-on. Our analysis of the stellar rotational velocity yields an inclination of 13-30deg, whereas i>20deg is needed for the system to be dynamically stable, which suggests a probable inclination range of 20-30deg. The spectral energy distribution is naturally reproduced with two dust rings associated with two planetesimal belts. The inner "asteroid belt" is located at ~10AU inside the orbit of the innermost companion and a "Kuiper belt" at >100AU is just exterior to the orbit of the outermost companion. The dust masses in the inner and outer ring are estimated to be ~1E-05 and 4E-02 M_earth, respectively. We show that all three planetary candidates may be stable in the mass range suggested in the discovery paper by Marois et al. 2008 (between 5 and 13 Jupiter masses), but only for some of all possible orientations. Stable orbits imply a double (4:2:1) mean-motion resonance between all three companions. We finally show that in the cases where the companions themselves are orbitally stable, the dust-producing planetesimal belts are also stable against planetary perturbations. Comment: 12 pages, 14 figures, 4 tables, accepted to be published in Astronomy & Astrophysics (May 20, 2009)
    Preview · Article · May 2009 · Astronomy and Astrophysics
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    ABSTRACT: We expand on the results of Nielsen et al. (2008), using the null result for giant extrasolar planets around the 118 target stars from the VLT NACO H and Ks band planet search (Masciadri et al. 2005), the VLT and MMT Simultaneous Differential Imaging (SDI) survey (Biller et al. 2007), and the Gemini Deep Planet Survey (Lafreniere et al. 2007) to set constraints on the population of giant extrasolar planets. Our analysis is extended to include the planet luminosity models of Fortney et al. (2008), as well as the correlation between stellar mass and frequency of giant planets found by Johnson et al. (2007). Doubling the sample size of FGKM stars strengthens our conclusions: a model for extrasolar giant planets with power-laws for mass and semi-major axis as giving by Cumming et al. (2008) cannot, with 95% confidence, have planets beyond 65 AU, compared to the value of 94 AU reported in Nielsen et al. (2008), using the models of Baraffe et al. (2003). When the Johnson et al. (2007) correction for stellar mass (which gives fewer Jupiter-mass companions to M stars with respect to solar-type stars) is applied, however, this limit moves out to 82 AU. For the relatively new Fortney et al. (2008) models, which predict fainter planets across most of parameter space, these upper limits, with and without a correction for stellar mass, are 182 and 234 AU, respectively. Comment: 67 pages, 16 figures, accepted to ApJ
    Preview · Article · Sep 2009 · The Astrophysical Journal
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    ABSTRACT: We present a pre-discovery H-band image of the HR 8799 planetary system that reveals all three planets in August 2007. The data were obtained with the Keck adaptive optics system, using angular differential imaging and a coronagraph. We confirm the physical association of all three planets, including HR 8799d, which had only been detected in 2008 images taken two months apart, and whose association with HR 8799 was least secure until now. We confirm that the planets are 2-3 mag fainter than field brown dwarfs of comparable near-infrared colors. We note that similar under-luminosity is characteristic of young substellar objects at the L/T spectral type transition, and is likely due to enhanced dust content and non-equilibrium CO/CH_4 chemistry in their atmospheres. Finally, we place an upper limit of 18 mag per square arc second on the >120 AU H-band dust-scattered light from the HR 8799 debris disk. The upper limit on the integrated scattered light flux is 1e-4 times the photospheric level, 24 times fainter than the debris ring around HR 4796A. Comment: ApJ Letters, in press; 13 pages, 3 figures, 1 table
    Full-text · Article · Oct 2009 · The Astrophysical Journal
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