Kepler-39b (formerly known as KOI-423b), is a confirmed

extrasolar object An ''extrasolar object'' ({{ety, la, extra, outside or beyond, , solaris, of the Sun) is an astronomical object that exists outside the Solar System. It is not applied to stars, or any other celestial object that is larger than a star or the Sola ...

(either a Jovian planet or

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

because of its mass) discovered orbiting the F-type star

Kepler-39 Kepler-39 (2MASS J19475046+4602034) is an F-type star, F-type main sequence star located in the constellation Cygnus (constellation), Cygnus. It is located about 3,560 light-years (1,090 parsecs) away. One known substellar companion orbits ...

. It is eighteen times more massive than Jupiter, and is about five fourths its size. The planet orbits its host star at about 15% of the average distance between the Earth and Sun. Kepler-39b's host star was investigated by European astronomers along with three other stars, including the host star of

Kepler-40b Kepler-40b, formerly known as KOI-428b, is a hot Jupiter discovered in orbit around the star Kepler-40, 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 da ...

, using equipment at the

Haute-Provence Observatory The Haute-Provence Observatory (OHP, french: Observatoire de Haute-Provence) is an astronomical observatory in the southeast of France, about 90 km east of Avignon and 100 km north of Marseille. It was established in 1937 as a national ...

in France. Collection and analysis of data in late 2010 led to the confirmation of Kepler-39b. The discovery paper was published in a journal on June 6, 2011. The location of the

subgiant star A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution o ...

in the night sky is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the object is compared to the celestial equator and is expressed in degrees. For Kepler-39, the location is 19h 47m 50.00 and 46° 02` 04.00 .

Characteristics

Mass, radius, and temperature

Kepler-39b is a Jupiter-like planet or brown dwarf that is eighteen times more massive than Jupiter and 1.22 times Jupiter's size. For a planet of its size, Kepler-39b has a relatively cool

equilibrium temperature The planetary equilibrium temperature is a theoretical temperature that a planet would be if it were a black body being heated only by its parent star. In this model, the presence or absence of an atmosphere (and therefore any greenhouse effect) is ...

of with respect to other inflated planets, defying most of the common models explaining inflation at the time of its discovery (including

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...

and the effect of stellar radiation). Although Kepler-39b and COROT-3b have similar characteristics (in terms of host star and mass), COROT-3b lies on the predicted size of what a planet of its character should look like. Kepler-39b is far larger than this model. A recent study reveals that Kepler-39b probably has a shape that is very oblate, which, if true, is very likely caused by its fast rotation. The estimated rotation period would be about 1.6 hours, very fast compared to about 10 hours for Jupiter and Saturn. Such a fast rotation also provides a natural explanation for its large radius.

Host star

Kepler-39 is an F-type star that is slightly larger and slightly more massive than the Sun (respectively, 1.10

solar mass The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

es and 1.39

solar radii Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.957\tim ...

) that is located 1090

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

s (3,560

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s) away from Earth. With an

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. Effective temperature is often used as an estimate of a body's surface temperature ...

of 6260 K, Kepler-39 is hotter than the Sun. Kepler-39 is significantly metal-poor, reflected in its

metallicity In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...

of e/H= -0.29 (51% the amount of iron found in the Sun). Kepler-39 has an

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

of 14.3, and is thus not visible with the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...

from Earth.

Orbital statistics

The planet orbits at a distance of 0.155 AU, equating to roughly 15% of the average distance between the Earth and Sun, completing one orbit every 21.0874 days. Kepler-39b has a modestly elliptical orbit, as described by its

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values betwee ...

of 0.121. Its

orbital inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth ...

is 88.83º, making the planet appear almost entirely edge-on to its host star as seen from Earth.

Discovery

The

Kepler Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws o ...

spacecraft is a

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

telescope equipped with photometric equipment. Launched in 2009, Kepler continuously watches 156,000 stars in a small area. A team of astronomers, hoping to learn more about

hot jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (). The close proximity to their stars and high surface-atmosphere temp ...

planets and

s, selected four F-type stars from the

Kepler Input Catalog The Kepler Input Catalog (or KIC) is a publicly searchable database of roughly 13.2 million targets used for the Kepler Spectral Classification Program (SCP) and ''Kepler''. Overview The Kepler SCP targets were observed by the 2MASS project ...

flagged as host to a Kepler Object of Interest (a transiting object that could possibly be a planet). Using three quarters of Kepler's data, the science team conducted a follow-up investigation in using the

SOPHIE échelle spectrograph The SOPHIE (Spectrographe pour l’Observation des Phénomènes des Intérieurs stellaires et des Exoplanètes, literally meaning "spectrograph for the observation of the phenomena of the stellar interiors and of the exoplanets") ''échelle spectrog ...

at the

in southern France, observing stars

Kepler-40 Kepler-40, formerly known as KOI-428, is an F-type star in the constellation Cygnus. Kepler-40 is known to host at least one planet, Kepler-40b. The star is approximately 1.5 times more massive than the Sun, and is over two times its si ...

, Kepler-39, KOI-552 and KOI-410. Of these, conclusive evidence of a planet orbiting KOI-410 could not be found, and KOI-552 was found to be a

binary star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

with an M-type companion. The

Hot Jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (). The close proximity to their stars and high surface-atmosphere temp ...

KOI-428b was the first of these four to be confirmed. SOPHIE collected thirteen

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

measurements of Kepler-39 between July 26, 2010 and September 10, 2010. Seven of the measurements were affected by moonlight, but were corrected. These radial velocity measurements conclusively eliminated the possibility that the observed dips in Kepler-39's brightness were caused by the movements of binary stars and confirming the existence of planet Kepler-39b in the process. SOPHIE's measurements were used to derive Kepler-39's

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...

, which was used to define Kepler-39b's characteristics. The astronomers submitted the discovery paper to ''

Astronomy and Astrophysics ''Astronomy & Astrophysics'' is a monthly peer-reviewed scientific journal covering theoretical, observational, and instrumental astronomy and astrophysics. The journal is run by a Board of Directors representing 27 sponsoring countries plus a re ...

'' on June 16, 2011 with François Bouchy as the leading author. The discovery paper covered the investigations of KOI-410 and KOI-552 along with the discovery of Kepler-39b.

References

{{2011 in space Giant planets Exoplanets discovered in 2011 Transiting exoplanets 39b Cygnus (constellation)