HD 17156

Starbox short
name = HD 17156
epoch = J2000.0
constell = Cassiopeia
ra = RA|02|49|44.49
dec = DEC|+71|45|11.64
spectral = G0IV
appmag_v = 8.17
absmag_v = 3.70
dist_ly = 255.19
dist_pc = 78.24
names = BD+71°171, HIP 13192, SAO 4737
Simbad = HD+17156

HD 17156 is a yellow subgiant star approximately 255 light-years away in the constellation of Cassiopeia. The apparent magnitude is 8.17, which means it is not visible to the naked eye but can be seen with good binoculars. The Sun to star distance is 255.19 ly or 78.24 pc.

The mass of the star is 20% more massive and 47% larger than our Sun. Based on its absolute magnitude of 3.70 and spectral type of G0, the star is thought to be hotter than the Sun. Based on the chromospheric observations, it was found that the age is 5.7 ± 1.3 billion years. [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 total lifetime of a 1.2 sol mass star should be 1.2 ^-2.5 × 10¹⁰, which is under 6.4 billion years; this star is in the last stage on the main sequence, and its nearby planets will soon be engulfed.

Based on spectral observations, the star was found to be metal-rich, 74% more metals than Sol. As of 2008, it is thought that two extrasolar planets orbit the star, but only one has been confirmed.

Planetary system

It is the first star in Cassiopeia around which an orbiting planet was discovered (in 2007). In February 2008, a second planet (HD 17156 c) was proposed, with a 5:1 mean motion resonance to the inner planet HD 17156 b.

PlanetboxOrbit
exoplanet = b
mass = 3.111
period = 21.21725
semimajor = 0.1594
eccentricity = 0.6717PlanetboxOrbit hypothetical
exoplanet = c
mass = 0.063
period = 111.314
semimajor = 0.481
eccentricity = 0.136

References

See also

* List of stars with extrasolar planets

External links

*
* [http://www.lpl.arizona.edu/~rory/research/xsp/dynamics/ Extrasolar Planet Interactions] by Rory Barnes & Richard Greenberg, Lunar and Planetary Lab, University of Arizona