|Extrasolar planet||List of extrasolar planets|
|Right ascension||(α)||19h 47m 50s|
|Declination||(δ)||+46° 02′ 04″|
|Mass||(m)||1.1 (± 0.07) M☉|
|Radius||(r)||1.39 (± 0.11) R☉|
|Temperature||(T)||6260 (± 140) K|
|Metallicity||[Fe/H]||-0.29 (± 0.1)|
|Age||5.08 (± 1.5) Gyr|
|Semimajor axis||(a)||0.155 (± 0.003) AU|
|Eccentricity||(e)||0.121 (± 0.023)|
|Orbital period||(P)||21.0874 (± 0.0002) d|
−2.6 g cm-3
|Discovery date||Published August 3, 2011|
|Discoverer(s)||François Bouchy et al.|
|Discovery method||radial velocity/transit|
KOI-423b is a Jupiter-like planet discovered in the orbit of F-type star KOI-423. KOI-423b is eighteen times more massive than Jupiter, and is about a five fourths its size. The planet orbits its host star at about 15% of the average distance between the Earth and Sun. KOI-423b's host star was investigated by European astronomers along with three other stars, including the host star of KOI-428b, using equipment at the Haute-Provence Observatory in France. Collection and analysis of data in late 2010 led to the confirmation of KOI-423b. The discovery paper was published in a journal on June 6, 2011.
The Kepler spacecraft is a NASA 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 planets and brown dwarfs, selected four F-type stars from the Kepler Input Catalog 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 at the Haute-Provence Observatory in southern France, observing stars KOI-428, KOI-423, 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 with an M-type companion. The Hot Jupiter KOI-428b was the first of these four to be confirmed.
SOPHIE collected thirteen radial velocity measurements of KOI-423 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 KOI-423's brightness were caused by the movements of binary stars and confirming the existence of planet KOI-423b in the process. SOPHIE's measurements were used to derive KOI-423's spectrum, which was used to define KOI-423b's characteristics.
The astronomers submitted the discovery paper to Astronomy 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 KOI-423b.
KOI-423 is an F-type star that is slightly larger and slightly more massive than the Sun (respectively, 1.10 solar masses and 1.39 solar radii) that is located 1200 parsecs (3,913 light years) away from Earth. With an effective temperature of 6260 K, KOI-423 is hotter than the Sun. KOI-423 is significantly metal-poor, reflected in its metallicity of [Fe/H] = -0.29 (51% the amount of iron found in the Sun).
KOI-423b is a Jupiter-like planet or brown dwarf that is eighteen times more massive than Jupiter and 1.22 times Jupiter's size. 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. KOI-423b has a modestly elliptical orbit, as described by its orbital eccentricity of 0.121. Its orbital inclination is 88.83º, making the planet appear almost entirely edge-on to its host star as seen from Earth.
For a planet of its size, KOI-423b has a relatively cool equilibrium temperature of 905 K with respect to other inflated planets, defying most of the common models explaining inflation at the time of its discovery (including convection and the effect of stellar radiation). Although KOI-423b 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. KOI-423b is far larger than this model.
A recent study reveals that KOI-423b 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.
- Jean Schneider (2011). "Notes for star KOI-423". Extrasolar Planets Encyclopaedia. Retrieved 14 September 2011.
- Bouchy; Bonomo; Santerne; Moutou; Deleuil; Diaz; Eggenberger; Ehrenreich et al. (2011). "SOPHIE velocimetry of Kepler transit candidates III. KOI-423b: An 18 Mjup transiting companion around an F7IV star". arXiv:1106.3225 [astro-ph.EP].
- Zhu, Wei; Huang, Chelsea; Zhou, George; Lin, D.N.C. "Constraining the Oblateness of Kepler Planets". Astrophysical Journal.