Wednesday 7 May 2014

Two Hot Jupiters found to be in triple star systems.

The discovery of a large number of Hot Jupiter type planets (large gas giant planets orbiting very close to their parent stars) in recent years has challenged out theories of stellar system formation. In theory gas giant type planets should only be able to form in the outer parts of a star system, beyond the 'snow line' where ice particles can accumulate within a protoplanetary disk. Since such planets could not form close to the stars, it was originally theorized that they must have formed in the outer part of the stellar system and then spiraled inwards for some reason. However this should lead to planets that still orbited in the plane on which the star rotated (plane of the stellar system), whereas many such planets seem to have orbits quite strongly tilted with regard to this plane. This has led to the development of two further theories, firstly that such systems could come about due to disruption of protoplanetary disks by strong magnetic fields from the host star, and the presence of undetected companion stars in the system, able to disrupt protoplanetary disks through gravitational torque.

In a paper published on the arXiv database at Cornell University Library on 30 March 2014, a team of scientists led by Eric Bechter of the Department of Physics at the University of Notre Dame describe the first results of the 'Friends of Hot Jupiters' program, which aims to systematically search for undetected companions to stars with known Hot Jupiters, with an emphasis on looking for dim Red Dwarfs (stars with masses less than 40% of that of the Sun) or Brown Dwarfs (which mass to fuse hydrogen in their cores like true stars, but are massive enough to fuse deuterium) detectable at infrared wavelengths.

Bechter et al. report the existence of new companion stars in two systems; WASP-12 and HAT-P-8, both of which were already known to be binary systems, with remote Red Dwarf companions orbiting the primary star. Both were directly imaged using the Keck II AO system at the W.M. Keck Observatory on Mauna Kea, Hawaii.

The Wasp-12 system was discovered in 2009. The primary star, WASP-12A, is a yellow dwarf star slightly larger than the Sun, roughly 800 light years from Earth in the constellation of Auriga. This is orbited by a planet, WASP-12b (when naming objects in other star systems stars are identified with upper case letters and planets lower case letters) with about 1.41 times the mass of Jupiter orbiting every 1.09 days at a distance of 0.0229 AU (2.29% of the distance at which the Earth orbits the Sun), this planet having an orbit tilted 59° to the plane of rotation of WASP-12A. In 2011 a second star was detected in the WASP-12 system, a red dwarf with approximately 38% of the Sun's mass named WASP-12B.  

Betcher et al. report closer examination of this companion star reveals that it also has a smaller companion, named WASP-12C, a red dwarf with 37% of the Sun's mass. These two stars orbit one-another at a distance of 21 AU.

Keck AO discovery image of WASP-12 B,C taken on 2 February 2012. North is up and east is left (east is reversed in astronomical images compared to standard maps, as the observer is looking up not down). Follow up observations separated by more than one year recovered the companion. Betcher et al. (2014).

The HAT-P-8 system was discovered in 2008. Its primary star, HAT-P-8A, is an F-type yellow-white dwarf star with roughly 1.28 times the mass of our Sun 750 light years from Earth in the constellation Pegasus. This is orbited every 3.08 days by a planet, HAT-P-8b with a mass 1.52 times as large as Jupiter at a distance of 0.487 AU (4.87% of the distance between the Earth and the Sun), the orbit of this planet being at 15° to the plane of the star's rotation. This system was found to have a companion star, HAT-P-8B, in 2011, this being an M-type red dwarf star with a mass 22% that of the Sun's.

Betcher et al. report the discovery of a third star in the system, HAT-P-8C, a smaller red dwarf with roughly 18% of the Sun's mass. This orbits HAT-P-8B at a distance of about 15 AU.

Keck AO discovery images of HAT-P-8 B,C taken on UT 24 June 2012. North is up and east is left. Follow up observations separated by more than one year recover the companion. Betcher et al. (2014).

See also...

KIC 11554435 (or Kepler Input Catalogue 11554435) is a young, sunlike star 652 light years from the Earth. It is thought to be between 200 and 300 million years old with a mass 98% of the Sun's and an effective surface temperature of ~5576 K, as opposed to 5778 K for the Sun. As a young star it rotates considerably faster than the Sun, roughly once every 5.4 days, while the Sun takes slightly under 24.5 days to complete a rotation, and has a high level of starspot activity (the same as sunspot activity but on a different star).

Wasp-12b is a super-Jovian Hot Jupiter type planet (a planet larger than Jupiter orbiting very close to its parent star) 871 light years from Earth in the constellation of Auriga. It orbits Wasp-12A, a G-type yellow dwarf star slightly bigger and hotter than our sun (1.35 × the Sun's mass, with a surface temperature of 6300 K, as opposed...

The HATNet (Hungarian made Automated Telescope Network) project uses eight small (11 cm diameter lens) telescopes located at the  Fred Lawrence Whipple Observatory in Arizona and the Mauna Kea Observatory in Hawaii, to search for exoplanets. Such Earth-based networks are playing an increasingly important role in...

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