Magnitude 8.71 Apparent magnitude (V) 8.71 | ||
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HD 147506 is a magnitude 8.7 F8 dwarf star that is somewhat larger and hotter than our sun. The star is approximately 370 light years from Earth and is positioned near the keystone of Hercules. It is estimated to be 2 to 3 billion years old.
Planetary system
Orbiting the star is HAT-P-2b, the most massive transiting extrasolar planet yet discovered. At 9.04 MJ and an estimated surface temperature of ~900 kelvins, on a 5.6 day orbit, this planet is unlike any previously discovered transiting planet. The planet has a large mass (nine times the mass of Jupiter), and a surface gravity 25 times that exerted by the Earth. Its orbital eccentricity is very large (e = 0.5). Since tidal forces should have reduced the orbital eccentricity of this planet it was speculated that another massive planet found outside the orbit of HAT-P-2b is in orbital resonance with HAT-P-2b. Additional measurements taken over six years show a long-term linear trend in the radial velocity data consistent with a companion of 15 Jupiter masses or greater. Adaptive optics images were taken at the Keck telescope and when combined with the radial velocity data show the maximum mass of the companion is that of an M dwarf star.
The planet was discovered by the HATNet Project and the researchers there believed the planet to be 10-20% larger than Jupiter. This discovery is important as it provides further support for the existing theory of planetary structure.