Kepler-70

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Kepler-70
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus[note 1]
Right ascension 19h 45m 25.47457s[1]
Declination +41° 05′ 33.8822″[1]
Apparent magnitude (V) 14.87[2]
Characteristics
Spectral type sdB[3]
Apparent magnitude (U) 13.80[2]
Apparent magnitude (B) 14.71[2]
Apparent magnitude (R) 15.43[2]
Apparent magnitude (I) 15.72[2]
Apparent magnitude (J) 15.36[2]
Apparent magnitude (H) 15.59[2]
Distance
3,590 ± 100 ly
(1,100 ± 30 pc)
Details
Mass0.496 ± 0.002[3] M☉
Radius0.203 ± 0.007[3] R☉
Luminosity (bolometric)22.9 ±  3.1 L☉
Temperature27,730 ± 260[3] K
UCAC3 263-170867, USNO-B1.0 1310-00349976.[2]
Database references
SIMBADdata
KICdata

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

apparent visual magnitude of 14.87.[2] This is too faint to be seen with the naked eye; viewing it requires a telescope with an aperture of 40 cm (20 in) or more.[4]
A subdwarf B star, Kepler-70 passed through the red giant 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. It has a relatively small radius of about 0.2 times the Sun's radius; white dwarfs are generally much smaller.[5] The star may be host to a planetary system with two planets,[6] although later research[7][8] indicates that this is not in fact the case.

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 14.87. Therefore, Kepler-70 is too dim to be seen with the naked eye.

Properties

Kepler-70 is an sdB (B-type subdwarf) star with a temperature of 27,730 K,[9] equivalent to that of a B0-type star, and nearly 6 times as hot as the surface temperature of the Sun, which has a surface temperature of 5,778 K.[10] It has a luminosity of 18.9 L☉,[11][9] a radius of 0.203 R☉, and a mass of 0.496 M☉. The star left the red-giant stage of its lifetime about 18.4 million years ago.[11][3]

Kepler-70 is still fusing.[9][11] When it runs out of helium, it will contract into a white dwarf.[11]

Planetary system

On December 21, 2011, evidence for two extremely short-period planets, Kepler-70b and Kepler-70c (also known as KOI-55 b and KOI-55 c), was announced by Charpinet et al. based on observations from the Kepler space telescope. 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.[6]

According to the main author of the paper in

pulsar planets have been observed, including PSR J1719−1438 b
which orbits closer to its host star, and consequently in a shorter time than, any other planet.

The two planets may have started out as a pair of

gas giants which spiraled inward toward their host star, which subsequently became a red giant. This engulfed the planets, evaporating all but their solid cores, which now orbit the sdB star.[12] Alternatively, there may only have been one gas giant engulfed in this way, with the rocky/metallic core having survived evaporation but fragmented inside the star. If this theory is correct, the two planets would be two large sections of the gas giant's core.[13]

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[7] suggested that what had been detected was not in fact the reflection of light from exoplanets, but stellar pulsation "visible beyond the cut-off frequency of the star." Further research[8] 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 would have a temperature of about 7288 K,[11] the same as that of an F0 star. The hottest confirmed exoplanet and the hottest with a measured temperature is KELT-9b, with a temperature of about 4,600 K.[14]

The Kepler-70 planetary system[6][note 2]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b (unconfirmed) 0.440 M🜨 0.0060 0.2401 — 20–80, likely 65° 0.759 R🜨
c (unconfirmed) 0.655 M🜨 0.0076 0.34289 — 20–80, likely 65° 0.867 R🜨

Notes

  1. ^ This is inferred from the RA and declination of the star.
  2. ^ Inclinations are derived from brightness variations and lack of transits. Radii are calculated assuming an albedo of 0.1.

References

  1. ^
    S2CID 244398875
    . Gaia DR3 record for this source at VizieR.
  2. ^ a b c d e f g h i "KPD 1943+4058". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 1 January 2012.
  3. ^ a b c d e "Notes for Planet KOI-55 b". Extrasolar Planets Encyclopaedia. Archived from the original on 19 January 2012. Retrieved 1 January 2012.
  4. ISBN 0-486-42820-6
  5. ^ Cain, Fraser (4 February 2009). "White Dwarf Stars". Universe Today. Retrieved 8 January 2012.
  6. ^
    S2CID 2213885
  7. ^
    doi:10.1051/0004-6361/201526346
  8. ^
    S2CID 182952925
  9. ^ a b c jamesrushford (2013-10-22). "Kepler 70b: The Coolest Exoplanet". PC 120: Life in the Universe. Retrieved 2021-07-27.
  10. ^ Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
  11. ^ a b c d e jarrettkong (2013-10-23). "Kepler-70b: The Remnant of a Time Long Past". PC 120: Life in the Universe. Retrieved 2021-07-27.
  12. ^ a b "Two More Earth-Sized Planets Discovered by Kepler, Orbiting Former Red Giant Star". Universe Today. 26 December 2011. Retrieved 1 January 2012.
  13. S2CID 119262095
  14. doi:10.1051/0004-6361/202243823
    .

External links
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