HD 17156b

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HD 17156b
Extrasolar planet List of extrasolar planets
Parent star
Star HD 17156
Constellation Cassiopeia
Right ascension (α) 02h 49m 44.49s
Declination (δ) +71° 45′ 11.64″
Distance 255.19 ly (78.24 pc)
Spectral type G0IV
Orbital elements
Semimajor axis (a) 0.1594+0.0012-0.0041[1] AU
Eccentricity (e) 0.6717+0.0028-0.0027[1]
Orbital period (P) 21.21725+0.00048-0.00043[1] d
Inclination (i) 88.23+0.017-0.05[1]°
Angular distance (θ) 2.037 mas
Longitude of
periastron		 (ω) 121.23+0.42-0.38[1]°
Time of periastron (T0) 2454438.4835±0.0025[1] JD
Semi-amplitude (K) 132.5 ± 9.5 m/s
Physical characteristics
Mass (m) 3.111+0.035-0.015[1] MJ
Radius (r) 0.964+0.016-0.027[1] RJ
Density (ρ) 3470+350-180[1] kg/m3
Surface gravity (g) 8.52[citation needed] m/s²
Temperature (T) 800-850[citation needed] K
Discovery information
Discovery date April 14, 2007
Discoverer(s) Fischer et al.
Detection method Radial velocity
& transit
Discovery site Hawaii, USA
Discovery status Published
To-scale diagram of the planet's orbit. The gray line indicates the transit window.
To-scale diagram of the planet's orbit. The gray line indicates the transit window.

HD 17156b is an exoplanet orbiting the star HD 17156. It is a superjovian planet slightly smaller than Jupiter but slightly larger than Saturn in a so-called "torched orbit". This highly-eccentric three-week orbit takes it approximately 0.0523 AU of the star at periastron before swinging out to approximately 0.2665 AU at apastron. Its eccentricity is about the same as 16 Cygni Bb, a so-called "eccentric Jupiter".

The planet was discovered on April 14, 2007 by a team using the radial velocity method on the Keck and Subaru telescopes.[2] The team made an initial, negative, transit search, but they were only able to cover 25% of the search space. This left the possibility of a transit open.

After the possibility of a transit was discussed on oklo.org, various groups performed a follow-on search. These searches confirmed a three-hour transit on October 2, 2007 and a paper was published two days later.[3]

HD 17156b is now the transiting planet with the longest orbital period. Follow-up investigations should reveal more precise orbital elements (as it did on Dec 13, 2007[1]), information on tidal forces and weather on the planet, and whether it is a good candidate for observation by the Spitzer Space Telescope.

[edit] References

  1. ^ a b c d e f g h i j Gillon, M. et al. (2007). "Improved parameters for the transiting planet HD 17156b: a high-density giant planet with a very eccentric orbit" arxiv:0712.2073 [astro-ph]. Retrieved on 2007-12-15.
  2. ^ Debra A. Fischer, Geoffrey W. Marcy, R. Paul Butler, Bun'ei Sato, Steven S. Vogt, Sarah Robinson, Gregory Laughlin, Gregory W. Henry, Shigeru Ida, Eri Toyota, Masashi Omiya, Peter Driscoll, Genya Takeda, Jason T. Wright, John A. Johnson (2007). "Five Intermediate-Period Planets from the N2K Sample". 
  3. ^ M. Barbieri, R. Alonso, G. Laughlin, J. M. Almenara, R. Bissinger, D. Davies, D. Gasparri, E. Guido, C. Lopresti, F. Manzini, and G. Sostero (Oct 4, 2007). "HD 17156b: A Transiting Planet with a 21.2 Day Period and an Eccentric Orbit" 6. 

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