| Discovery | |
|---|---|
| Discovered by | François Bouchyet al.[1] |
| Discovery site | Haute-Provence[1] |
| Discovery date | Published August 3, 2011[1] |
| radial velocity/transit[1] | |
| Orbital characteristics | |
| 0.155 (± 0.003)[2]AU | |
| Eccentricity | 0.121 (± 0.023)[2] |
| 21.0874 (± 0.0002)[2]d | |
| Inclination | 88.83+0.59 −0.4[2] |
| 98.9+5.9 −6.8[2] | |
| Star | Kepler-39 |
| Physical characteristics | |
| 1.07±0.03[3]RJ | |
| Mass | 18.00+0.93 −0.91[1]MJ |
Meandensity | 12.40+3.4 −2.6[1]gcm−3 |
| Temperature | 905 K (632 °C; 1,169 °F)[1] |
Kepler-39b (formerly known asKOI-423b), is a confirmedextrasolar object (either a Jovian planet orbrown dwarf because of its mass) discovered orbiting the F-type starKepler-39. 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 ofKepler-40b, using equipment at theHaute-Provence Observatory 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 thesubgiant star in the night sky is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on theEarth. 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 .
Kepler-39b is a Jupiter-like planet or brown dwarf that is eighteen times moremassive than Jupiter and 1.22 times Jupiter's size.For a planet of its size, Kepler-39b has a relatively coolequilibrium temperature of 905 K (632 °C; 1,169 °F) with respect to other inflated planets, defying most of the common models explaining inflation at the time of its discovery (includingconvection and the effect of stellar radiation).[1] Although Kepler-39b andCOROT-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.[1] 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.[4] 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.[4]
In 2022, the radius of Kepler-39b was improved based on directparallax measaurements by theGaia spacecraft, which allows the distance to the host star to be known. The newly-determined radius of1.07 RJ is slightly lower than the previous estimate of1.22 RJ.[3]
Kepler-39 is anF-type star that is slightly larger and slightly more massive than the Sun (respectively, 1.10solar masses and 1.39solar radii) that is located 1090parsecs (3,560light years) away from Earth. With aneffective temperature of 6260 K, Kepler-39 is hotter than the Sun. Kepler-39 is significantly metal-poor, reflected in itsmetallicity of [Fe/H] = -0.29 (51% the amount of iron found in the Sun).[2]
Kepler-39 has anapparent magnitude of 14.3, and is thus not visible with thenaked eye from Earth.[2]
The planet orbits at a distance of 0.155AU, equating to roughly 15% of theaverage distance between the Earth and Sun, completing one orbit every 21.0874 days. Kepler-39b has a modestly elliptical orbit, as described by itsorbital eccentricity of 0.121. Itsorbital inclination is 88.83º, making the planet appear almost entirely edge-on to its host star as seen from Earth.[2]
TheKepler spacecraft is aNASA telescope equipped withphotometric equipment. Launched in 2009, Kepler continuously watches 156,000 stars in a small area. A team of astronomers, hoping to learn more abouthot jupiter planets andbrown dwarfs, selected four F-type stars from theKepler Input Catalog flagged as host to aKepler 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 theSOPHIE échelle spectrograph at theHaute-Provence Observatory in southern France, observing starsKepler-40, 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 abinary star with anM-type companion. TheHot JupiterKOI-428b was the first of these four to be confirmed.[1]
SOPHIE collected thirteenradial velocity 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'sspectrum, which was used to define Kepler-39b's characteristics.[1]
The astronomers submitted the discovery paper toAstronomy and Astrophysics 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.[1]
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