Kepler-70, also known as KIC 5807616 and formerly as KOI-55, is a

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

in the constellation Cygnus with an

apparent visual 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 lig ...

of 14.87, and is 4200

light-years 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 ...

away. This is too faint to be seen with the naked eye; viewing it requires a telescope with an

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An opt ...

of or more. A subdwarf B star, Kepler-70 passed through the

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around or ...

stage some 18.4 million years ago. In its present-day state, it is fusing helium in its core. Once it runs out of helium it will contract to form a

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes fro ...

. It has a relatively small radius of about 0.2 times the Sun's radius; white dwarfs are generally much smaller. The star may be host to a planetary system with two planets, although later research indicates that this is not in fact the case. If they are confirmed to exist, then the innermost planet has the highest temperature of any known planet.

Properties

Kepler-70 is an sdB (B-type

subdwarf A subdwarf, sometimes denoted by "sd", is a star with luminosity class VI under the Yerkes spectral classification system. They are defined as stars with luminosity 1.5 to 2 magnitudes lower than that of main-sequence stars of the same spectral ...

star with a temperature of 27,730 K, equivalent to that of a B0-type star. It has a luminosity of , a radius of , and a mass about half of that of the sun. The star was an evolutionary giant less than 20 million years ago. Kepler-70 is still fusing. When it runs out of helium, it will contract into a white dwarf.

Planetary system

On December 26, 2011, evidence for two extremely short-period planets,

Kepler-70b Kepler-70b (formerly known as its Kepler Object of Interest designation ''KOI-55.01''; sometimes listed as KOI-55 b) is one of two postulated exoplanets orbiting the subdwarf B star (sdB) Kepler-70. The other planet is Kepler-70c, and both planet ...

and

Kepler-70c Kepler-70c (formerly called KOI-55.02; sometimes listed as KOI-55 c) is one of two postulated exoplanets orbiting the sdB star Kepler-70. Their discovery was announced in 2011. However, later research suggests that the two exoplanets probably do ...

, was announced by Charpinet et al. They were detected by the reflection of starlight caused by the planets themselves, rather than through a variation in apparent stellar magnitude caused by them transiting the star. The measurements also suggested a smaller body between the two candidate planets; this remains unconfirmed. If these planets exist, then the orbits of Kepler-70b and Kepler-70c have 7:10 orbital resonance and have the closest approach between planets of any known planetary system. However, later research suggested that what had been detected was not in fact the reflection of light from exoplanets, but star pulsation "visible beyond the cut-off frequency of the star." Further research indicated that star pulsation modes were indeed the more likely explanation for the signals found in 2011, and that the two exoplanets probably did not exist. If Kepler-70b exists, then it has a temp of 7288 K, the same as that of an F0 star.

Notes

References

External links

Kepler mission discoveries
{{2011 in space Cygnus (constellation) 55 Hypothetical planetary systems Planetary transit variables B-type subdwarfs