 Size comparison of HD 17156 b with Jupiter. | |
| Discovery | |
|---|---|
| Discovered by | Fischeret al.[1] |
| Discovery site | W. M. Keck Observatory Subaru Telescope |
| Discovery date | 14 April 2007 |
| Radial velocity andTransit | |
| Orbital characteristics | |
| 0.1589 AU (23,770,000 km)[2] | |
| Eccentricity | 0.6768 ± 0.0034[3] |
| 21.2163979 ± 0.0000159[3]d | |
| Inclination | 86.573 ± 0.060[3] |
| 2454438.4835±0.0025[2] | |
| 121.71 ± 0.43[3] | |
| Semi-amplitude | 274.2 ± 2.0[3] |
| Star | HD 17156 |
| Physical characteristics | |
| 1.0870 ± 0.0066[3]RJ | |
| Mass | 3.191 ± 0.033[3]MJ |
Meandensity | 3.47 g/cm3[2] |
| 67.0 ± 2.4 m/s2 (219.8 ± 7.9 ft/s2)[3] | |
| Temperature | ? |
HD 17156 b, namedMulchatna by theIAU,[4] is anextrasolar planet approximately 255light-years away in theconstellation ofCassiopeia. The planet was discovered orbiting theyellow subgiantstarHD 17156 in April 2007. The planet is classified as a relatively coolhot Jupiter planet slightly smaller than Jupiter but slightly larger than Saturn. This highly-eccentric three-week orbit takes it approximately 0.0523AU of the star atperiastron before swinging out to approximately 0.2665 AU atapastron. Its eccentricity is about the same as16 Cygni Bb, a so-called "eccentric Jupiter". Until 2009, HD 17156 b was the transiting planet with the longest orbital period.[5]
The planet was discovered on April 14, 2007, by a team using theradial velocity method on theKeck andSubaru telescopes.[1] 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 onoklo.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.[6]
The planet was originally named "HD 17156 b", being the second object in the HD 17156 system.
The planet was given the name "Mulchatna" by theIAU, chosen by United States representatives for theNameExoWorlds content, with the comment that "TheMulchatna River is a tributary of theNushagak River in southwestern Alaska, USA".[4] Its parent star was simultaneously named Nushagak in the contest.
Careful radial velocity measurements have made it possible to detect theRossiter–McLaughlin effect, the shifting in photospheric spectral lines caused by the planet occulting a part of the rotating stellar surface. This effect allows the measurement of the angle between the planet's orbital plane and the equatorial plane of the star.[7] This planet's spin-orbit angle was initially measured by Narita in 2007 as +62 ± 25 but has been remeasured by Cochran +9.4 ± 9.3 degrees.[8] The study in 2012, refined the misalignemt angle to 10±5.1°.[9]
Due to its high eccentricity and large distance from its star, HD 17156 b has a low probability of ever entering asecondary eclipse.[2][10] The star's true temperature cannot be measured with accuracy. Due to the high eccentricity of its orbit, the atmosphere of HD 17156 b undergoes a 27-fold variation in stellar flux during each orbit.[11]
Media related toHD 17156 b at Wikimedia Commons
