| Discovery | |
|---|---|
| Discovered by | Alexandre Santerne et al.[1] |
| Discovery site | Haute-Provence Observatory[1] |
| Discovery date | 4 January 2011 (published)[1] |
| Transit method[1] | |
| Orbital characteristics | |
| Star | Kepler-40 |
| Physical characteristics | |
| 1.17 (± 0.04)[1]RJ 13.12[2]R🜨 | |
| Mass | 2.2 (± 0.4)[1]MJ (700[2]M🜨) |
Meandensity | 1.68+0.53 −0.43[1]gcm−3 |
| Temperature | 2327+195 −669K.[3] |
Kepler-40b, formerly known asKOI-428b, is ahot Jupiter discovered in orbit around the starKepler-40, which is about to become ared giant. The planet was first noted as a transit event byNASA'sKepler spacecraft. The Kepler team made data collected by its satellite publicly available, including data on Kepler-40; French and Swiss astronomers used the equivalent to one night of measurements on theSOPHIE échelle spectrograph to collect all the data needed to show that a planet was producing the periodic dimming of Kepler-40.[1] The planet, Kepler-40b, is twice the mass ofJupiter and slightly larger than it in size, making it as dense asNeptune. The planet is also nearly thirteen times hotter than Jupiter and orbits five times closer to its star thanMercury is from the Sun.
Kepler-40 was first observed by the Kepler spacecraft, aNASA satellite that searches for planetsin 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 resultinglight curve was made available to the public by the Kepler science team, revealing four transit events over 33.5 days.[1]
A team composed of astronomers from France and Switzerland used theSOPHIE échelle spectrograph at theHaute-Provence Observatory in southern France to examine Kepler-40. SOPHIE usesradial velocity measurements to examine stars for exoplanets. After background light was removed and alternative causes for radial velocity variations were disproved (for example, that Kepler-40 was actually a close binary star), the team used SOPHIE to analyze the properties of the actual star.[1] The astronomers observing the star found that it is nearing themain sequence turn-off (the star fuses the last of its hydrogen and becomes ared giant). The establishment of stellar parameters helped the astronomers extrapolate the exoplanet's parameters and prove the existence of Kepler-40b.[1] 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 includingKepler-5 andKepler-7.[1]
The discovery of Kepler-40b 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 Kepler-40b's existence and parameters.[1] Kepler-40b was published in the journalAstronomy and Astrophysics on January 4, 2011, after it was sent to the journal on September 15, 2010.[1]
Kepler-40 is anF-type evolved subgiant star located in theCygnus constellation. The star is 1.48 times themass of the Sun and 2.13 times itsradius. With aneffective temperature of 6510K, Kepler-40 is larger, more massive, more diffuse, and hotter than the Sun is. Themetallicity of Kepler-40, [Fe/H] = 0.10, means that it has 25.9 % more iron than is measured in the Sun.[2] Kepler-40 is nearing the main sequence turn-off; in other words, it is about to fuse the last of its hydrogen and become ared giant.[1]
Kepler-40 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 approximately 2500parsecs (8100light years) away from Earth.
Kepler-40b is aHot Jupiter that is estimated to be 2.2 times themass of Jupiter (over 700 times themass of Earth), but 1.17 timesJupiter's radius (13.12 times theradius of Earth). Thus, the planet has a density of 1.68 grams per cubic centimeter, similar to that ofNeptune (1.638 g/cm3).[4] The planet'sequilibrium temperature was initially estimated to be 1620 K, thirteen times hotter than Jupiter's equilibrium temperature.[2] In 2015, the planetary nightside temperature was modeled to be even hotter at 2327+195
−669K.[3]
Kepler-40b orbits its star every 6.87 days at anaverage distance of 0.081AU. It also has anorbital inclination of 89.7°, meaning that it can be seen nearly edge-on with respect to Earth.[2] In comparison,Mercury orbits the Sun every 87.97 days at an average distance of 0.387 AU;[5] therefore, Kepler-40b'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.