HAT-P-8b

HAT-P-8b is an extrasolar planet located approximately 720 light years away in the constellation of Pegasus, orbiting the 10th magnitude star GSC 02757-01152. This planet was discovered by transit on December 5, 2008. Despite the designation as HAT-P-8b, it is the 11th planet discovered by the HATNet Project. The mass of the planet is 50% more than Jupiter while the radius is also 50% more than Jupiter. The mass of this planet is exact since the inclination of the orbit is known, typical for transiting planets. This is a so-called “hot Jupiter” because this Jupiter-like gas giant planet orbits in a really close torch orbit around the star, making this planet extremely hot (in the order of a thousand kelvins). The distance from the star is roughly 20 times smaller than that of Earth from the Sun, which places the planet roughly 8 times closer to its star than Mercury is from the Sun. The “year” on this planet lasts only 3 days, 1 hour, 49 minutes, and 54 seconds, compared with Earth's 365 days, 6 hours, 9 minutes, and 10 seconds in a sidereal year.[3]

HAT-P-8b
Size comparison of HAT-P-8b with Jupiter.
Discovery
Discovered byHATNet Project
Discovery dateDecember 5, 2008
Transit
Orbital characteristics
0.04496+0.00046
−0.00045 AU
Eccentricity<0.0060[1]
3.0763458±0.0000024[2] d
Inclination87.5+1.9
−0.9
StarGSC 02757-01152
Physical characteristics
Mean radius
1.5+0.08
−0.06 RJ
Mass1.354±0.035[1] MJ

    The study in 2012, utilizing a Rossiter–McLaughlin effect, have determined the planetary orbit is mildly misaligned with the rotational axis of the star, misalignment equal to -17+9.2
    −11.5    °.[4]

    References
    1. Bonomo, A. S.; et al. (2017). "The GAPS Programme with HARPS-N at TNG . XIV. Investigating giant planet migration history via improved eccentricity and mass determination for 231 transiting planets". Astronomy and Astrophysics. 602. A107. arXiv:1704.00373. Bibcode:2017A&A...602A.107B. doi:10.1051/0004-6361/201629882.
    2. Mancini, L.; et al. (2013). "A lower radius and mass for the transiting extrasolar planet HAT-P-8 b". Astronomy and Astrophysics. 551. A11. arXiv:1212.3701. Bibcode:2013A&A...551A..11M. doi:10.1051/0004-6361/201220291.
    3. Latham, David W.; et al. (2009). "Discovery of a Transiting Planet and Eight Eclipsing Binaries in HATNet Field G205". The Astrophysical Journal. 704 (2): 1107–1119. arXiv:0812.1161. Bibcode:2009ApJ...704.1107L. doi:10.1088/0004-637X/704/2/1107.
    4. Obliquities of Hot Jupiter host stars: Evidence for tidal interactions and primordial misalignments, 2012, arXiv:1206.6105

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