WASP-15b
Encyclopedia
WASP-15b is an extrasolar planet
discovered in 2008 by the SuperWASP
collaboration, which seeks to discover exoplanets that transit their host stars. The planet orbits its host star at a distance of 0.05 AU
every four days. The mass of this planet is about one half that of Jupiter
, but its radius is nearly 50% larger than Jupiter's, making the density of this planet only one quarter that of water; it is thought that some other form of heating must explain its extremely low density. WASP-15b's discovery was published on April 29, 2009.
project, which operates from the South African Astronomical Observatory
, between May 4, 2006 and July 17, 2006. It was later observed by both WASP-South and SuperWASP-North, which is based in the Canary Islands, from January 31, 2007 to July 17, 2007 and from January 31, 2008 to May 29, 2008. Further analysis taken from 24,943 collected data points revealed eleven full or partial transits.
Follow-up observations were conducted by a European and American science team at the 1.2 m Leonhard Euler Telescope
at La Silla Observatory
in Chile, which further raised the possibility of the existence of a planet in WASP-15's orbit; use of the CORALIE spectrograph
on the Euler Telescope between March 6, 2008 and July 17, 2008 revealed that the variations in radial velocity measurements
were not because of an eclipsing binary star system.
CORALIE and the High Resolution Echelle Spectrometer (HIRES) revealed the spectrum of WASP-15, which was used to derive the star's characteristics. The science team studying WASP-15 found that, after running best-fit models, WASP-15's radial velocity and transit shifts were most likely due to the existence of a planet.
WASP-15's planet, WASP-15b, had one of the lowest densities known amongst extrasolar planets when it was discovered. Its discovery paper was published by the American Astronomical Society
on April 29, 2009 in the Astronomical Journal
.
constellation. It is located approximately 308 parsec
s (1,004 light years) from Earth and has an apparent magnitude
of 10.9, making it invisible to the unaided eye. The star is 1.18 times more massive
than the Sun, and has a radius that is 1.477 times larger than that of the Sun, making it more diffuse. WASP-15 has an effective temperature
of 6300 K, and is thus hotter than the Sun, although at 3.9 billion years, it is also younger. WASP-15 has a metallicity
of [Fe/H] of -0.17, which means that it has 68% of the iron found in the Sun.
of 0.542 times Jupiter's mass and a radius that is 1.428 times Jupiter's radius. Due in part to its proximity to its host star, a distance of 0.0499 AU (7,500,000 km), WASP-15b is greatly inflated, with a density of 0.247 g/cm3. Another factor, such as an internal heat source, is suspected to add to this extremely high radius and extremely low density. WASP-15b orbits its host star every 3.7520656 days. It also has an orbital inclination of 85.5º, making it almost edge-on as seen from the Earth's perspective.
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
discovered in 2008 by the SuperWASP
SuperWASP
SuperWASP is an international academic organisation performing an ultra-wide angle search for transiting extrasolar planets with the aim of covering the entire sky down to ~15th magnitude.-Equipment:...
collaboration, which seeks to discover exoplanets that transit their host stars. The planet orbits its host star at a distance of 0.05 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
every four days. The mass of this planet is about one half that of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
, but its radius is nearly 50% larger than Jupiter's, making the density of this planet only one quarter that of water; it is thought that some other form of heating must explain its extremely low density. WASP-15b's discovery was published on April 29, 2009.
Discovery
WASP-15 was first observed by the WASP-South branch of the SuperWASPSuperWASP
SuperWASP is an international academic organisation performing an ultra-wide angle search for transiting extrasolar planets with the aim of covering the entire sky down to ~15th magnitude.-Equipment:...
project, which operates from the South African Astronomical Observatory
South African Astronomical Observatory
South African Astronomical Observatory is the national center for optical and infrared astronomy in South Africa. It was established in 1972. The observatory is run by the National Research Foundation of South Africa. The facility's function is to conduct research in astronomy and astrophysics...
, between May 4, 2006 and July 17, 2006. It was later observed by both WASP-South and SuperWASP-North, which is based in the Canary Islands, from January 31, 2007 to July 17, 2007 and from January 31, 2008 to May 29, 2008. Further analysis taken from 24,943 collected data points revealed eleven full or partial transits.
Follow-up observations were conducted by a European and American science team at the 1.2 m Leonhard Euler Telescope
Leonhard Euler Telescope
Leonhard Euler Telescope, or Swiss 1.2-m Leonhard Euler Telescope, is a diameter aperture reflecting telescope at the Geneva Observatory at La Silla Observatory. It is use for astronomy, and runs the CORALIE echelle spectrograph to search for planets. Its first planet discovery was of one in orbit...
at La Silla Observatory
La Silla Observatory
La Silla Observatory is an astronomical observatory in Chile with three telescopes built and operated by the European Southern Observatory organisation, and several others are partly maintained by ESO...
in Chile, which further raised the possibility of the existence of a planet in WASP-15's orbit; use of the CORALIE spectrograph
CORALIE spectrograph
The CORALIE spectrograph is an echelle type spectrograph used for astronomy. This instrument used with a telescope to measure star spectra for the Doppler effect to detect the presence of extrasolar planets by the radial velocity method...
on the Euler Telescope between March 6, 2008 and July 17, 2008 revealed that the variations in radial velocity measurements
Doppler spectroscopy
Doppler spectroscopy, also known as radial velocity measurement, is a spectroscopic method for finding extrasolar planets. It involves the observation of Doppler shifts in the spectrum of the star around which the planet orbits....
were not because of an eclipsing binary star system.
CORALIE and the High Resolution Echelle Spectrometer (HIRES) revealed the spectrum of WASP-15, which was used to derive the star's characteristics. The science team studying WASP-15 found that, after running best-fit models, WASP-15's radial velocity and transit shifts were most likely due to the existence of a planet.
WASP-15's planet, WASP-15b, had one of the lowest densities known amongst extrasolar planets when it was discovered. Its discovery paper was published by the American Astronomical Society
American Astronomical Society
The American Astronomical Society is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC...
on April 29, 2009 in the Astronomical Journal
Astronomical Journal
The Astronomical Journal is a peer-reviewed monthly scientific journal owned by the American Astronomical Society and currently published by Institute of Physics Publishing. It is one of the premier journals for astronomy in the world...
.
Host star
WASP-15 is an F-type star located in the HydraHydra (constellation)
Hydra is the largest of the 88 modern constellations, measuring 1303 square degrees. It has a long history, having been included among the 48 constellations listed by the 2nd century astronomer Ptolemy. It is commonly represented as a water snake...
constellation. It is located approximately 308 parsec
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
s (1,004 light years) from Earth and has an apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
of 10.9, making it invisible to the unaided eye. The star is 1.18 times more massive
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
than the Sun, and has a radius that is 1.477 times larger than that of the Sun, making it more diffuse. WASP-15 has an effective temperature
Effective temperature
The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation...
of 6300 K, and is thus hotter than the Sun, although at 3.9 billion years, it is also younger. WASP-15 has a metallicity
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
of [Fe/H] of -0.17, which means that it has 68% of the iron found in the Sun.
Characteristics
WASP-15b has a massJupiter mass
Jupiter mass , is the unit of mass equal to the total mass of the planet Jupiter . Jupiter mass is used to describe masses of the gas giants, such as the outer planets and extrasolar planets. It is also used in describing brown dwarfs....
of 0.542 times Jupiter's mass and a radius that is 1.428 times Jupiter's radius. Due in part to its proximity to its host star, a distance of 0.0499 AU (7,500,000 km), WASP-15b is greatly inflated, with a density of 0.247 g/cm3. Another factor, such as an internal heat source, is suspected to add to this extremely high radius and extremely low density. WASP-15b orbits its host star every 3.7520656 days. It also has an orbital inclination of 85.5º, making it almost edge-on as seen from the Earth's perspective.
External links
- http://www.superwasp.org/wasp_planets.htm