KOI-428b
Encyclopedia
KOI-428b is a Hot Jupiter
-type planet discovered in the orbit of the star KOI-428
, which is about to become a red giant
. The planet was first noted as a transit event by NASA
's Kepler spacecraft. The Kepler team made data collected by its satellite publicly available, including data on KOI-428; French and Swiss astronomers used the equivalent to one night of measurements on the SOPHIE échelle spectrograph
to collect all the data needed to show that a planet was producing the periodic dimming of KOI-428. The planet, KOI-428b, is twice the mass of Jupiter
and slightly larger than it in size, making it as dense as Neptune
. The planet is also nearly thirteen times hotter than Jupiter and orbits five times closer to its star than Mercury
does to the Sun.
satellite that searches for planets in transit (crossing in front of and dimming) their host stars, from May 13, 2009, to June 15, 2009 in its first days of operation. The resulting light curve
was made available to the public by the Kepler science team, revealing four transit events over 33.5 days.
A team composed of astronomers from France and Switzerland used the SOPHIE échelle spectrograph
at the Haute-Provence Observatory
in southern France to examine KOI-428. SOPHIE uses radial velocity measurements to examine stars for exoplanets. After background light was removed and alternative causes for radial velocity variations were disproved (for example, that KOI-428 was actually a close binary star), the team used SOPHIE to analyze the properties of the actual star. The astronomers observing the star found that it is nearing the main sequence
turn-off (the star fuses the last of its hydrogen and becomes a red giant
). The establishment of stellar parameters helped the astronomers extrapolate the exoplanet's parameters and prove the existence of KOI-428b. The discovered planet was the sixth transiting planet to have been discovered in orbit around stars with a radius of more than 1.8 times that of the Sun, after planets including Kepler-5
and Kepler-7
.
The discovery of KOI-428b demonstrated that smaller telescopes, such as SOPHIE, are effective when used as follow-ups to space missions like Kepler. The team of astronomers spent what amounted roughly to one night on a 1.93d-meter telescope and gathered all the data needed to establish KOI-428b's existence and parameters. KOI-428b was published in the journal Astronomy and Astrophysics
on January 4, 2011, after it was sent to the journal on September 15, 2010.
constellation. The star is 1.48 times the mass
of the Sun and 2.13 times its radius. With an effective temperature
of 6510 K, KOI-428 is larger, more massive, more diffuse, and hotter than the Sun is. The metallicity
of KOI-428, [Fe/H] = 0.10, means that it has 25.9% more iron than is measured in the Sun. KOI-428 is nearing the main sequence turn-off; in other words, it is about to fuse the last of its hydrogen and become a red giant
.
KOI-428 hosts the sixth planetary system to be discovered in the orbit of a star with a mass of over 1.8 solar masses. It lies 2700 parsec
s (8806.4 light years) away from Earth, making it more distant than any previously verified planet discovered by Kepler, and has an apparent magnitude
of 14.58. Thus, it is invisible to the unaided eye.
that is estimated to be 2.2 times the mass of Jupiter
(over 700 times the mass of Earth
), but 1.17 times Jupiter's radius (13.12 times the radius of Earth
). Thus, the planet has a density of 1.68 grams per cubic centimeter, similar to that of Neptune
(1.638 g/cm3). The planet's equilibrium temperature is estimated to be 1620 K, thirteen times hotter than Jupiter's equilibrium temperature.
KOI-428b orbits its star every 6.87 days at an average distance of 0.081 AU
. It also has an orbital inclination of 89.7°, meaning that it can be seen nearly edge-on with respect to Earth. In comparison, Mercury
orbits the Sun every 87.97 days at an average distance of 0.387 AU; therefore, KOI-428's orbit is approximately thirteen times faster than that of Mercury's and five times closer to its host star than Mercury is to the Sun.
Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
-type planet discovered in the orbit of the star KOI-428
KOI-428
KOI-428 is an F-type star with one known planet, KOI-428b, in orbit. The star is approximately 1.5 times more massive than the Sun, and is over two times its size; it was, at upon its discovery, the largest and the most evolved star yet discovered with a transiting planet in its orbit...
, which is about to become a red giant
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
. The planet was first noted as a transit event by NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's Kepler spacecraft. The Kepler team made data collected by its satellite publicly available, including data on KOI-428; French and Swiss astronomers used the equivalent to one night of measurements on the SOPHIE échelle spectrograph
SOPHIE échelle spectrograph
The SOPHIE échelle spectrograph is a high-resolution echelle spectrograph installed on the 1.93m reflector telescope at the Haute-Provence Observatory located in south-eastern France...
to collect all the data needed to show that a planet was producing the periodic dimming of KOI-428. The planet, KOI-428b, is twice the mass 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,...
and slightly larger than it in size, making it as dense as Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
. The planet is also nearly thirteen times hotter than Jupiter and orbits five times closer to its star than Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
does to the Sun.
Observational history
KOI-428 was first observed by the Kepler spacecraft, a NASANASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
satellite that searches for planets in transit (crossing in front of and dimming) their host stars, from May 13, 2009, to June 15, 2009 in its first days of operation. The resulting light curve
Light curve
In astronomy, a light curve is a graph of light intensity of a celestial object or region, as a function of time. The light is usually in a particular frequency interval or band...
was made available to the public by the Kepler science team, revealing four transit events over 33.5 days.
A team composed of astronomers from France and Switzerland used the SOPHIE échelle spectrograph
SOPHIE échelle spectrograph
The SOPHIE échelle spectrograph is a high-resolution echelle spectrograph installed on the 1.93m reflector telescope at the Haute-Provence Observatory located in south-eastern France...
at the Haute-Provence Observatory
Haute-Provence Observatory
The Observatoire de Haute-Provence was established in 1937 as a national facility for French astronomers. Astronomical observations began in 1943 using the 1.20 m telescope, and the first research papers based on observations made at the observatory were published in 1944...
in southern France to examine KOI-428. SOPHIE uses radial velocity measurements to examine stars for exoplanets. After background light was removed and alternative causes for radial velocity variations were disproved (for example, that KOI-428 was actually a close binary star), the team used SOPHIE to analyze the properties of the actual star. The astronomers observing the star found that it is nearing the main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
turn-off (the star fuses the last of its hydrogen and becomes a red giant
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
). The establishment of stellar parameters helped the astronomers extrapolate the exoplanet's parameters and prove the existence of KOI-428b. The discovered planet was the sixth transiting planet to have been discovered in orbit around stars with a radius of more than 1.8 times that of the Sun, after planets including Kepler-5
Kepler-5
Kepler-5 is a star located in the constellation Cygnus in the field of view of the Kepler Mission, a NASA project aimed at detecting planets in transit of, or passing in front of, their host stars as seen from Earth. One closely orbiting, Jupiter-like planet, named Kepler-5b, has been detected...
and Kepler-7
Kepler-7
Kepler-7 is a star located in the constellation Lyra in the field of view of the Kepler Mission, a NASA operation in search of Earth-like planets. It is home to the fourth of the first five planets that Kepler discovered; this planet, a Jupiter-size gas giant named Kepler-7b, is as light as styrofoam...
.
The discovery of KOI-428b demonstrated that smaller telescopes, such as SOPHIE, are effective when used as follow-ups to space missions like Kepler. The team of astronomers spent what amounted roughly to one night on a 1.93d-meter telescope and gathered all the data needed to establish KOI-428b's existence and parameters. KOI-428b was published in the journal Astronomy and Astrophysics
Astronomy and Astrophysics
* Astronomy and Astrophysics has a 2010 impact factor of 4.410.-See also:*The Astronomy and Astrophysics Review*Advanced Satellite for Cosmology and Astrophysics*Astronomy & Geophysics*Astronomical Journal*Astrophysical Journal...
on January 4, 2011, after it was sent to the journal on September 15, 2010.
Host star
KOI-428 is an F-type star located in the CygnusCygnus (constellation)
Cygnus is a northern constellation lying on the plane of the Milky Way. Its name is the Latinized Hellenic word for swan. One of the most recognizable constellations of the northern summer and autumn, it features a prominent asterism known as the Northern Cross...
constellation. The star is 1.48 times the mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
of the Sun and 2.13 times its radius. With 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 6510 K, KOI-428 is larger, more massive, more diffuse, and hotter than the Sun is. The 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 KOI-428, [Fe/H] = 0.10, means that it has 25.9% more iron than is measured in the Sun. KOI-428 is nearing the main sequence turn-off; in other words, it is about to fuse the last of its hydrogen and become a red giant
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
.
KOI-428 hosts the sixth planetary system to be discovered in the orbit of a star with a mass of over 1.8 solar masses. It lies 2700 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 (8806.4 light years) away from Earth, making it more distant than any previously verified planet discovered by Kepler, 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 14.58. Thus, it is invisible to the unaided eye.
Characteristics
KOI-428b is a Hot JupiterHot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
that is estimated to be 2.2 times the mass of Jupiter
Jupiter 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....
(over 700 times the mass of Earth
Earth mass
Earth mass is the unit of mass equal to that of the Earth. 1 M⊕ = 5.9722 × 1024 kg. Earth mass is often used to describe masses of rocky terrestrial planets....
), but 1.17 times Jupiter's radius (13.12 times the radius of Earth
Earth radius
Because the Earth is not perfectly spherical, no single value serves as its natural radius. Distances from points on the surface to the center range from 6,353 km to 6,384 km...
). Thus, the planet has a density of 1.68 grams per cubic centimeter, similar to that of Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
(1.638 g/cm3). The planet's equilibrium temperature is estimated to be 1620 K, thirteen times hotter than Jupiter's equilibrium temperature.
KOI-428b orbits its star every 6.87 days at an average distance of 0.081 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
. It also has an orbital inclination of 89.7°, meaning that it can be seen nearly edge-on with respect to Earth. In comparison, Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
orbits the Sun every 87.97 days at an average distance of 0.387 AU; therefore, KOI-428's orbit is approximately thirteen times faster than that of Mercury's and five times closer to its host star than Mercury is to the Sun.