|Exoplanet||List of exoplanets|
|Star||HAT-P-1 (ADS 16402 B)|
|Right ascension||(α)||22h 57m 47s|
|Declination||(δ)||+38° 40′ 30″|
|Distance||453 ± 65 ly
(139 ± 20 pc)
|Spectral type||G0V |
|Semi-major axis||(a)||0.0553 ± 0.0014 AU|
|Orbital period||(P)||4.4652934 ± 0.0000093 d|
|Inclination||(i)||86.28 ± 0.20°|
|Time of transit||(Tt)||2,454,363.94656 ± 0.00072 JD|
|Semi-amplitude||(K)||59.3 ± 1.4 m/s|
|Mass||(m)||0.524 ± 0.031 MJ|
|Radius||(r)||1.225 ± 0.059  RJ|
|Discovery date||Thurs, Sept 14, 2006|
|Discovery method||Transit, radial velocity|
|Discovery site||Arizona and Hawaii|
HAT-P-1b is an extrasolar planet orbiting the Sun-like star HAT-P-1, also known as ADS 16402 B. HAT-P-1 is the dimmer component of the ADS 16402 binary star system. It is located 453 light years away from Earth in the constellation Lacerta. HAT-P-1b is among the least dense of any of the known extrasolar planets.
HAT-P-1b was detected by searching for astronomical transits of the parent star by orbiting planets. As the planet passes in front of its parent star (as seen from Earth), it blocks a small amount of the light reaching us from the star. HAT-P-1b was first detected by a dip of 0.6% in the light from the star. This enabled determination of the planet's radius and orbital period. The discovery was made by the HATNet Project (Hungarian Automated Telescope Network) using telescopes in Arizona and Hawaii and announced on September 14, 2006.
Orbit and mass
HAT-P-1b is located in a very close orbit to its star, taking only 4.47 days to complete. It therefore falls into the category of hot Jupiters. At only 8.27 million kilometers from the star, tidal forces would circularise the orbit unless another perturbing body exists in the system. At the present time, the existing measurements are not sufficient to determine the orbital eccentricity, so a perfectly circular orbit has been assumed by the discoverers. However, the eccentricity of the planet was calculated to be no greater than 0.067.
In order to determine the mass of the planet, measurements of the star's radial velocity variations were made by the N2K Consortium. This was done by observing the Doppler shift in the star's spectrum. Combined with the known inclination of the orbit as determined by the transit observations, this revealed the mass of the planet to be 0.53±0.04 times that of Jupiter.
As evidenced by its high mass and planetary radius, HAT-P-1b is a gas giant, most likely composed primarily of hydrogen and helium. The planet would thus have no well-defined surface. Current theories predict that such planets formed in the outer regions of their solar systems and migrated inwards to their present orbits.
HAT-P-1b is significantly larger than predicted by theoretical models. This may indicate the presence of an additional source of heat within the planet. One possible candidate is tidal heating from an eccentric orbit, a possibility which has not been ruled out from the available measurements. However, another planet with a significantly inflated radius, HD 209458 b, is in a circular orbit.
An alternative possibility is that the planet has a high axial tilt, like Uranus in the Solar System. The problem with this explanation is that it is thought to be quite difficult to get a planet into this configuration, so having two such planets among the set of known transiting planets is problematic.
- Bakos, G. Á.; et al. (2007). "HAT-P-1b: A Large-Radius, Low-Density Exoplanet Transiting One Member of a Stellar Binary". The Astrophysical Journal. 656 (1): 552–559. arXiv:. Bibcode:2007ApJ...656..552B. doi:10.1086/509874.
- Johnson, John Asher; et al. (2008). "Measurement of the Spin-Orbit Angle of Exoplanet HAT-P-1b". The Astrophysical Journal. 686 (1): 649–657. arXiv:. Bibcode:2008ApJ...686..649J. doi:10.1086/591078.
- "Oversize Orb: Puffy planet poses puzzle". Science News Online. Archived from the original on 2007-10-13. Retrieved 2007-10-14.
- "A HAT trick". Retrieved 2007-10-14.
- Winn, Joshua N. (2008). "Measuring accurate transit parameters". Proceedings of the International Astronomical Union. 4: 99. arXiv:. doi:10.1017/S174392130802629X.
- Jackson, Brian; Richard Greenberg; Rory Barnes (2008). "Tidal Heating of Extra-Solar Planets". ApJ. 681 (2): 1631. arXiv:. Bibcode:2008ApJ...681.1631J. doi:10.1086/587641.
Media related to HAT-P-1b at Wikimedia Commons
- Harvard-Smithsonian Center for Astrophysics Press Release
- BBC News
- HATnet official homepage
- NY Times
- A Celestia image of HAT-P-1b compared to Jupiter