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Extrasolar planet List of extrasolar planets 300pxSize comparison of HR 8799 b (gray) with Jupiter. HD 218396 b[7]
Database references

HR 8799 b is an extrasolar planet located approximately 129 light-years away in the constellation of Pegasus, orbiting the 6th magnitude Lambda Boötis star HR 8799. It has a mass between 4 and 7 [6]Jupiter masses and a radius from 10 to 30% larger than Jupiter's. It orbits at 68 AU from HR 8799 (or 7 AU inside the inner edge of the dust disk orbiting the star) with an unknown eccentricity and a period of 460 years, and is the outermost known planet in the HR 8799 system. Along with two other planets orbiting HR 8799, the planet was discovered on November 13, 2008 by Marois et al., using the Keck and Gemini observatories in Hawaii. These planets were discovered using the direct imaging technique.[5][8][9][10][11]

In 2009 it was discovered that the Hubble Space Telescope had in fact directly imaged HR 8799 b eleven years earlier, in 1998, suggesting that more exoplanets might be revealed through analysis of HST photographic archives.[12] Additional precovery images were also obtained by reanalyzing data taken in 2002 at the Subaru Telescope and in 2005 and 2007 at the W.M Keck Observatory [13] [14] .[15]

Broadband photometry of HR 8799 b shows that it has thicker clouds in its atmosphere than do older, higher surface gravity substellar objects of the same effective temperature.[16] Near infrared H band and K band spectroscopy of HR8799b published in May 2011 indicate a hydrogen rich, dusty atmosphere with disequilibrium CO / CH4 chemistry.[17]

Near infrared spectroscopy from 995 to 1769 nanometers made with the Palomar Obervatory show evidence of Ammonia and/or Acetylene as well as Carbon Dioxide, but little Methane.[18]

## NotesEdit

1. 1.0 1.1 Computed from parallax: $\scriptstyle \mathrm{distance\ in\ parsecs}=\frac{1000}{\mathrm{parallax\ in\ milliarcseconds}}$
2. 2.0 2.1 Calculated from the separations in the East and North directions which are 1.528 and 0.798 arcseconds respectively.
3. 3.0 3.1 Value given assuming the planet's orbit is circular and is being observed face-on.

## ReferencesEdit

1. 1.0 1.1 1.2 V* V342 Peg -- Variable Star of gamma Dor type, entry, SIMBAD. Accessed on line November 14, 2008.
2. 2.0 2.1 van Leeuwen, F. (2007). HIP 114189. Hipparcos, the New Reduction. Retrieved 2008-10-13.
3. Gray, R.O. and Kaye, A.B. (1999). HR 8799: A Link between γ Doradus Variables and λ Bootis Stars. The Astronomical Journal 118 (6): 2993–2996.
4. Kaye, A.B. (1999). Gamma Doradus Stars: Defining a New Class of Pulsating Variables. PASP 111 (761): 840–844.
5. 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 Marois, Christian (November 2008). Direct Imaging of Multiple Planets Orbiting the Star HR 8799. Science 322 (5906): 1348–1352.
6. 6.0 6.1 Template:Cite arxiv
7. HD 218396b -- Extra-solar Planet Candidate, entry, SIMBAD. Accessed on line December 6, 2008.
8. Script error
9. Script error
10. Template:Cite news
11. Fabrycky (1 December 2008). Stability of the directly imaged multiplanet system HR 8799: resonance and masses. Astrophys.J. 710 (2): 1408–1421.
12. Lafrenière (18 February 2009). HST/NICMOS detection of HR 8799 b in 1998. The Astrophysical Journal 694 (2): L148–L152.
13. Fukagawa, Misato (July 2012). H-Band Image of a Planetary Companion Around HR 8799 in 2002. ApJL 696: 1.
14. Metchev, Stanimir (November 2009). Pre-Discovery 2007 Image of the HR 8799 Planetary System. ApJL 696 (2): 1.
15. Currie, Thayne (July 2012). Direct Detection and Orbital Analysis of the Exoplanets HR 8799 bcd from Archival 2005 Keck/NIRC2 Data. ApJL 755 (2): 34.
16. Currie, Thayne (March 2011). A Combined Subaru/VLT/MMT 1--5 Micron Study of Planets Orbiting HR 8799: Implications for Atmospheric Properties, Masses, and Formation. ApJ 729 (2): 128.
17. Template:Cite paper
18. Oppenheimer, B. R.. Reconnaissance of the HR 8799 Exosolar System I: Near IR Spectroscopy.