HR 8799 e

Exoplanet Parent star Orbital elements List of exoplanets Star HR 8799 Constellation Pegasus Right ascension (α) 23h 07m 28.7150s[1] Declination (δ) +21° 08′ 03.302″[1] Apparent magnitude (mV) 5.964[1] Distance 129 ± 4[2][note 1] ly (39 ± 1[2][note 1] pc) Spectral type kA5 hF0 mA5 V; λ Boo[3][4] Observed separation Angular separation (ρ) 368 ± 9[5] mas Projected separation (d) 14.5 ± 0.5, 14.8 ± 0.5 [5][6] AU Semi-major axis (a) ~ 14.5 ± 0.5[5][note 2] AU (~ 2175 Gm) Orbital period (P) ~ 50[5][note 2] y Mass (m) 7-9 [6] MJ Radius (r) 1.2 RJ Temperature (T) 1,000 [7] Discovery date November 1, 2010 (announced) November 22, 2010 (published) Discoverer(s) Marois et al. Discovery method Direct imaging Discovery site Keck and Gemini observatories in Hawaii Discovery status Published[5] HD 218396 e[8] Database references Extrasolar Planets Encyclopaedia data SIMBAD data Exoplanet Archive data Open Exoplanet Catalogue data

HR 8799 e is a large exoplanet, orbiting the star HR 8799, which lies 129 lightyears from Earth. This gas giant is between 5 and 10 times the mass of Jupiter,[5] the largest planet in the Solar System. Due to their young age and high temperature all four discovered planets in the HR 8799 system are large, compared to all gas giants in the Solar System.

Description

HR 8799 e is the fourth planet orbiting HR 8799 in order of discovery. It is a young, hot and massive gas giant, and is fairly close to its star, lying just between the orbits of Saturn and Uranus in the Solar System. The planet is still glowing red hot.[5]

HR 8799 e is the innermost known planet as it orbits closer to its star than the other three known planets in this planetary system. This planet orbits at an estimated distance of 14.5 AU based on the relationship between angular separation measured by direct imaging observations and the star's distance from Earth. The estimated period of this planet if the orbit is face-on is about 50 years.[5]

Discovery

A team of researchers led by Christian Marois at the National Research Council's Herzberg Institute of Astrophysics identified the planet from data taken in 2009 and 2010 using the W.M. Keck Observatory in the K and L spectral bands.[5] They announced their findings on November 22, 2010. A separate work reporting the detection of HR 8799 e, led by Thayne Currie and using the Very Large Telescope, was made public six weeks later.[6] Observations obtained since then with the Large Binocular Telescope show that HR 8799 e has a spectrum and temperature similar to HR 8799 c and d.[7]

Spectra

Near infrared spectroscopy from 995 to 1769 nanometers made with the Palomar Obervatory show evidence of Methane and Acetylene but no Ammonia or Carbon Dioxide. There is currently no explanation why this planet shows strong methane absorption, but the other 3 planets in this system do not, despite all 4 planets having similar atmospheric temperatures.[9]

Notes

1. ^ a b Computed from parallax: ${\displaystyle \scriptstyle \mathrm {distance\ in\ parsecs} ={\frac {1000}{\mathrm {parallax\ in\ milliarcseconds} }}}$
2. ^ a b Value given assuming the planet's orbit is circular and is being observed face-on.

References

1. ^ a b c V* V342 Peg -- Variable Star of gamma Dor type, entry, SIMBAD. Accessed on line November 14, 2008.
2. ^ a b van Leeuwen, F. (2007). "HIP 114189". Hipparcos, the New Reduction. Retrieved 2008-10-13.
3. ^ Gray, R.O.; Kaye, A.B. (1999). "HR 8799: A Link between γ Doradus Variables and λ Bootis Stars". The Astronomical Journal. 118 (6): 2993–2996. Bibcode:1999AJ....118.2993G. doi:10.1086/301134.
4. ^ Kaye, A.B.; et al. (1999). "Gamma Doradus Stars: Defining a New Class of Pulsating Variables". PASP. 111 (761): 840–844. arXiv:. Bibcode:1999PASP..111..840K. doi:10.1086/316399.
5. Marois, C.; Zuckerman, B.; Konopacky, Q. M.; MacIntosh, B.; Barman, T. (2010). "Images of a fourth planet orbiting HR 8799". Nature. 468 (7327): 1080–1083. arXiv:. Bibcode:2010Natur.468.1080M. doi:10.1038/nature09684. PMID 21150902.
6. ^ a b c Currie, Thayne; et al. (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. arXiv:. Bibcode:2011ApJ...729..128C. doi:10.1088/0004-637x/729/2/128.
7. ^ a b Skemer, Andrew; et al. (July 2012). "First Light LBT AO Images of HR 8799 bcde at 1.6 and 3.3 μm: New Discrepancies between Young Planets and Old Brown Dwarfs". ApJ. 753 (1): 14. arXiv:. Bibcode:2012ApJ...753...14S. doi:10.1088/0004-637x/753/1/14.
8. ^ HD 218396e – Extra-solar Planet Candidate, entry, SIMBAD. Accessed on line December 11, 2010.
9. ^ Oppenheimer, B. R. (2013). "Reconnaissance of the HR 8799 Exosolar System I: Near IR Spectroscopy". The Astrophysical Journal. 768: 24. arXiv:. doi:10.1088/0004-637X/768/1/24.