HD 17156 b

Planetbox begin
name = HD 17156 bPlanetbox star
star = HD 17156
constell = Cassiopeia
RA=RA|02|49|44.49
DEC=DEC|+71|45|11.64
dist_ly = 255.19
dist_pc = 78.24
class=G0IVPlanetbox orbit
semimajor = 0.1589 Cite arXiv|author=Gillon, M. "et al."|title=Improved parameters for the transiting planet HD 17156b: a high-density giant planet with a very eccentric orbit
eprint=0712.2073v3|class=astro-ph|year=2007|accessdate=2008-08-24]
eccentricity = 0.6719
period = 21.21747
inclination = 85.4
ang_dist = 2.037
long_peri = 121.23
t_peri = 2454438.4835±0.0025
semi-amp = 132.5 ± 9.5Planetbox character
mass = 3.09
radius =1.23
density = 3470
gravity = ~8.52
temperature = ?Planetbox discovery
discovery_date = 14 April 2007
discoverers = Fischer "et al."
discovery_site = flag|United States
discovery_method = Radial velocity and Transit
discovery_status = Published

HD 17156 b is an extrasolar planet 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 planet 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". HD 17156 b is now the transiting planet with the longest orbital period.

The planet was discovered on April 14, 2007 by a team using the radial velocity method on the Keck and Subaru telescopes. [cite journal | url=http://www.journals.uchicago.edu/doi/abs/10.1086/521869 | author=Fischer "et al." | title=Five Intermediate-Period Planets from the N2K Sample | journal=The Astrophysical Journal | volume=669 | issue=2 | year=2007 | pages=1336–1344 | doi=10.1086/521869 | format=abstract [http://arxiv.org/abs/0704.1191 web preprint] ] 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 [http://www.oklo.org/?p=242 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. [cite journal | url=http://www.aanda.org/articles/aa/abs/2007/47/aa8787-07/aa8787-07.html | author=Barbieri "et al." | title=HD 17156b: A Transiting Planet with a 21.2 Day Period and an Eccentric Orbit | journal=Astronomy and Astrophysics |year=2007 | volume=476 | pages=L13–L16 ( [http://xxx.lanl.gov/abs/0710.0898 web Preprint] )]

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. [cite journal | author=Cochran, W. D., Redfield, S., Endl, M., & Cochran |title=The Spin-Orbit Alignment of the HD 17156 Transiting Eccentric Planetary System| journal=The Astrophysical Journal Letters | volume= 683 | page=L59–L62 |year=2008 |month=August 10] By analogy with HD 149026 b, a low angle would imply the formation of the planet was peaceful and probably involved interactions with the protoplanetary disc. A much larger angle suggests a violent interplay with other protoplanets. Given its eccentricity the latter is equally probable until the discrepancy of the Rossiter results is resolved.

It is so distant from its star and eccentric, that it will never enter a secondary eclipse relative to Earth, of the planet behind the star. [cite journal | url=http://www.journals.uchicago.edu/doi/abs/10.1086/588461 | author=Jonathan Irwin, David Charbonneau, and Philip Nutzman | title=Parameters and Predictions for the Long-Period Transiting Planet HD 17156b | journal=The Astrophysical Journal | volume=681 | pages=636–643 | year=2008 | month=July] The star's true temperature, and so the planet's surface temperature, cannot be measured with accuracy.

See also

* 16 Cygni Bb
* HD 17156 c

References

External links

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