HD 17156 b, named Mulchatna by the

IAU The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach ...

, is an

extrasolar planet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

approximately 255 light-years away in the constellation of Cassiopeia. The planet was discovered orbiting the yellow subgiant star HD 17156 in April 2007. The planet is classified as a relatively cool

hot Jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (). The close proximity to their stars and high surface-atmosphere tem ...

planet slightly smaller than Jupiter but slightly larger than Saturn. This highly-eccentric three-week orbit takes it approximately 0.0523 AU of the star at

periastron An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any elli ...

before swinging out to approximately 0.2665 AU at

apastron An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any el ...

. Its eccentricity is about the same as

16 Cygni Bb 16 Cygni Bb or HD 186427 b is an extrasolar planet approximately away in the constellation of Cygnus. The planet was discovered orbiting the Sun-like star 16 Cygni B, one of two solar-mass () components of the triple star system 16 Cygni in 1 ...

, a so-called "

eccentric Jupiter An eccentric Jupiter is a Jovian planet that orbits its star in an eccentric orbit. Note: this study treats eccentric Jupiters as giant planets having an orbital eccentricity of 0.1 or greater. Eccentric Jupiters may probably disqualify a plane ...

". Until 2009, HD 17156 b was the transiting planet with the longest orbital period.

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 o
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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.

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

, chosen by United States representatives for the

NameExoWorlds NameExoWorlds (also known as IAU NameExoWorlds) is the name of various projects managed by the International Astronomical Union (I.A.U.) to encourage names to be submitted for astronomical objects, which would later be considered for official ad ...

content, with the comment that "The Mulchatna River is a tributary of the

Nushagak River The Nushagak River ( esu, Iilgayaq) is a river in southwest Alaska, United States. It begins in the Alaska Range and flows southwest to Nushagak Bay, an inlet of Bristol Bay, east of Dillingham, Alaska. The Mulchatna River is a major tributa ...

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 Rossiter–McLaughlin effect is a spectroscopic phenomenon observed when an object moves across the face of a star. Description The Rossiter–McLaughlin effect is a spectroscopic phenomenon observed when either an eclipsing binary's secon ...

, 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°. 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.

References

External links

{{Sky, 02, 49, 44.49, +, 71, 45, 11.64, 255.19 Cassiopeia (constellation) Transiting exoplanets Giant planets Exoplanets discovered in 2007 Exoplanets detected by radial velocity Exoplanets with proper names

Discovery

Name

Orbit

See also

References

External links