WASP-15
Encyclopedia
WASP-15 is a magnitude
11 star
located about 1000 light-year
s away in the constellation
Hydra
. The star, which is more massive, larger, hotter, and more luminous than the Sun
, is also less metal-rich than the Sun. WASP-15 has one known planet in its orbit, WASP-15b
; the planet is a Hot Jupiter
with an anomalously high radius, a phenomenon which may be explained by the presence of an internal heat source. The star was first observed by the SuperWASP
program in 2006; future measurements in 2007 and 2008, as well as follow-up observations and analysis, eventually led to the discovery of WASP-15b using the transit method and Doppler spectroscopy
.
, which coordinates the planet-searching SuperWASP
program in the Southern Hemisphere (WASP-South), and was catalogued by its brightness and its coordinates in the sky. This information was captured first with one camera field between May 4, 2006 and July 17, 2006, and later again using two overlapping camera fields between January 31, 2007 to July 7, 2007 and from January 31, 2008 to May 29, 2008.
Data processing led to the acquisition of 24,943 data points that suggested that some body transited, or crossed in front of (and briefly dimmed), WASP-15 every 3.7520 days. Approximately eleven transits, full and partial, were observed. Use of the EulerCAM photometer
at the La Silla Observatory
's 1.2 m Leonhard Euler Telescope
on March 29, 2008 provided further evidence for an exoplanet by better defining the transit's curve. Later, the CORALIE spectrograph
(also on the Euler telescope) between March 6, 2008 and July 17, 2008 used Doppler spectroscopy
to collect 21 radial velocity measurements. Analysis confirmed the presence of a planet that was later designated WASP-15b
.
that is 1.18 times larger than the Sun, and a radius that is 1.477 bigger. It is, thus, larger, more massive, and more diffuse than the Sun. The star has an effective temperature
of 6300 K, making it also hotter than the Sun. With a metallicity
of [Fe/H] = -0.17, WASP-15 has 0.676 times the amount of iron than the Sun, and has consistently lower levels of other metals, including sodium, magnesium, silicon, calcium, and scandium. In addition, WASP-15 is most likely younger than the Sun, as it has an estimated age of 3.9 billion years. WASP-15 is approximately 3.09 times more luminous than the Sun.
WASP-15 is located at a distance of 308 parsec
s (1,004 light years), and it has an estimated apparent magnitude
of 10.9. It is, thus, not visible from Earth with the unaided eye.
. The planet, which is a Hot Jupiter
, orbits its host star at a distance of 0.0499 AU
every 3.7520656 days. WASP-15b was noted by its discoverers because of its anomalously high radius, which is 1.428 times that of Jupiter, compared to its mass, which is 0.542 times the size of Jupiter. WASP-15b's large radius cannot be explained solely by its proximity to its star, suggesting that some form of tidal heating
or other internal heating mechanism is also involved.
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...
11 star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
located about 1000 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Hydra
Hydra (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...
. The star, which is more massive, larger, hotter, and more luminous than the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, is also less metal-rich than the Sun. WASP-15 has one known planet in its orbit, WASP-15b
WASP-15b
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 planet is a Hot Jupiter
Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
with an anomalously high radius, a phenomenon which may be explained by the presence of an internal heat source. The star was first observed 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:...
program in 2006; future measurements in 2007 and 2008, as well as follow-up observations and analysis, eventually led to the discovery of WASP-15b using the transit method and Doppler spectroscopy
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....
.
Observational history
WASP-15 was first observed by the South African Astronomical ObservatorySouth 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...
, which coordinates the planet-searching 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:...
program in the Southern Hemisphere (WASP-South), and was catalogued by its brightness and its coordinates in the sky. This information was captured first with one camera field between May 4, 2006 and July 17, 2006, and later again using two overlapping camera fields between January 31, 2007 to July 7, 2007 and from January 31, 2008 to May 29, 2008.
Data processing led to the acquisition of 24,943 data points that suggested that some body transited, or crossed in front of (and briefly dimmed), WASP-15 every 3.7520 days. Approximately eleven transits, full and partial, were observed. Use of the EulerCAM photometer
Photometer
In its widest sense, a photometer is an instrument for measuring light intensity or optical properties of solutions or surfaces. Photometers are used to measure:*Illuminance*Irradiance*Light absorption*Scattering of light*Reflection of light*Fluorescence...
at the 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...
's 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...
on March 29, 2008 provided further evidence for an exoplanet by better defining the transit's curve. Later, 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...
(also on the Euler telescope) between March 6, 2008 and July 17, 2008 used Doppler spectroscopy
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....
to collect 21 radial velocity measurements. Analysis confirmed the presence of a planet that was later designated WASP-15b
WASP-15b
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...
.
Characteristics
WASP-15 is an F-type star with a massSolar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
that is 1.18 times larger than the Sun, and a radius that is 1.477 bigger. It is, thus, larger, more massive, and more diffuse than the Sun. The star 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, making it also hotter than the Sun. With 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] = -0.17, WASP-15 has 0.676 times the amount of iron than the Sun, and has consistently lower levels of other metals, including sodium, magnesium, silicon, calcium, and scandium. In addition, WASP-15 is most likely younger than the Sun, as it has an estimated age of 3.9 billion years. WASP-15 is approximately 3.09 times more luminous than the Sun.
WASP-15 is located at a distance of 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), and it has an estimated 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. It is, thus, not visible from Earth with the unaided eye.
Planetary system
WASP-15 is host to the planet WASP-15bWASP-15b
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 planet, which is a Hot Jupiter
Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
, orbits its host star at a distance of 0.0499 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
every 3.7520656 days. WASP-15b was noted by its discoverers because of its anomalously high radius, which is 1.428 times that of Jupiter, compared to its mass, which is 0.542 times the size of Jupiter. WASP-15b's large radius cannot be explained solely by its proximity to its star, suggesting that some form of tidal heating
Tidal heating
Tidal heating occurs through the tidal friction processes: orbital and rotational energy are dissipated as heat in the crust of the moons and planets involved. Io, a moon of Jupiter, is the most volcanically active body in the solar system, with no impact craters surviving on its surface...
or other internal heating mechanism is also involved.