HAT-P-1b

Planetbox begin
name=HAT-P-1 bPlanetbox star
star=ADS 16402 B
constell=Lacerta
RA=22^h 57^m 47^s
DEC=+38° 40′ 30″
dist_ly=453 ± 65
dist_pc=139 ± 20
class=G0V Planetbox orbit
semimajor=0.0553 ± 0.0014
period=4.4652934 ± 0.000093
eccentricity=<0.067
long_peri=0
t_transit=2,453,984.397 ± 0.009
inclination=86.28 ± 0.2
semi-amp=59.9 ± 1.8Planetbox character
mass=0.524 ± 0.031
radius=1.36 ± 0.11/0.09
density=≈261.36
gravity_earth=0.922Planetbox discovery
discoverers=HATNet Project
discovery_date=Thurs, Sept 14, 2006
discovery_method=Transit, radial velocity
discovery_site=Arizona and Hawaii
discovery_status=Published

HAT-P-1 b is an extrasolar planet orbiting the Sunlike star ADS 16402 B. ADS 16402 B 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-1 b is among the least dense of any of the known extrasolar planets.

Discovery

HAT-P-1 b 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-1 b 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.cite web|url=http://www.sciencenews.org/articles/20060916/fob5.asp|title=Oversize Orb: Puffy planet poses puzzle|accessdate=2007-10-14|publisher=Science News Online]

Orbit and mass

HAT-P-1b is located in a very close orbit to its star, taking only 4.47 days to complete. cite journal | url = http://www.journals.uchicago.edu/doi/abs/10.1086/509874 | author = Bakos "et al." | title = HAT-P-1b: A Large-Radius, Low-Density Exoplanet Transiting One Member of a Stellar Binary | journal = The Astrophysical Journal | volume=656 | issue=1 | year=2007 | pages=552–559 ( [http://xxx.lanl.gov/abs/astro-ph?papernum=0609369 web Preprint] ) ] 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.cite web|url=http://oklo.org/?p=138|title=A HAT trick|accessdate=2007-10-14] 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.

Rotation

As of August 2008, the most recent calculation of HAT-P-1b's Rossiter-McLaughlin effect and so spin-orbit angle was that of Johnson. [cite arXiv | title= Measuring accurate transit parameters | author=Joshua N. Winn | eprint=0807.4929v2 |class=astro-ph |year=2008] This is +3.6 ± 2.0 degrees. [cite arXiv | title=Measurement of the Spin-Orbit Angle of Exoplanet HAT-P-1b | author=Johnson "et al." | eprint=0806.1734 |class=astro-ph |year=2008]

Characteristics

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 currently holds a record for being the least dense extrasolar planet discovered, and 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. [cite journal|title=Tidal Heating of Extra-Solar Planets| first= Brian| last= Jackson| coauthors= Richard Greenberg, Rory Barnes| journal=ApJ| id=arXiv|0803.0026 | year=2008 ] 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 our 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.

References

External links

* [http://www.cfa.harvard.edu/press/pr0624.html Harvard-Smithsonian Center for Astrophysics Press Release]
* [http://news.bbc.co.uk/2/hi/science/nature/5346998.stm BBC News]
* [http://www.hatnet.hu HATnet official homepage]
* [http://www.nytimes.com/2006/09/15/science/space/15planet.html?ex=1315972800&en=3646d4e6a10ec036&ei=5089&emc=rss NY Times]