HD 17156 b
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Discovery
The planet was discovered on April 14, 2007, by a team using the radial velocity method on the Keck and Subaru telescopes. 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.
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Name
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 the IAU, chosen by United States representatives for the NameExoWorlds content, with the comment that "The Mulchatna River is a tributary of the Nushagak River in southwestern Alaska, USA". Its parent star was simultaneously named Nushagak in the contest.
Orbit
Careful radial velocity measurements have made it possible to detect the Rossiter–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. 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. The study in 2012, refined the misalignemt angle to 10±5.1°.
Due to its high eccentricity and large distance from its star, HD 17156 b has a low probability of ever entering a secondary eclipse. 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.