Kepler-70

Kepler-70, also known as KIC 5807616 and formerly as KOI-55, is a star in the constellation Cygnus with an apparent visual magnitude of 14.87,[3] and is 4200 light-years away. 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. If they are confirmed to exist, then the innermost planet has the highest temperature of any known planet.

Kepler-70

The Kepler-70 system if confirmed
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus[1][note 1]
Right ascension 19h 45m 25.4746s[2]
Declination +41° 5′ 33.8820″[2]
Apparent magnitude (V) 14.87[3]
Characteristics
Spectral type sdB[1]
Apparent magnitude (U) 13.80[3]
Apparent magnitude (B) 14.71[3]
Apparent magnitude (R) 15.43[3]
Apparent magnitude (I) 15.72[3]
Apparent magnitude (J) 15.36[3]
Apparent magnitude (H) 15.59[3]
Astrometry
Proper motion (μ) RA: 7.185±0.061[2] mas/yr
Dec.: −3.134±0.060[2] mas/yr
Parallax (π)0.7850 ± 0.0314 mas[2]
Distance4,200 ± 200 ly
(1,270 ± 50 pc)
Details
Mass0.496 ± 0.002[1] M☉
Radius0.203 ± 0.007[1] R☉
Luminosity (bolometric)22.9 ±  3.1 L☉
Temperature27,730 ± 260[1] K
Other designations
2MASS J19452546+4105339, KIC 5807616, KOI-55, UCAC2 46165657, UCAC3 263-170867, USNO-B1.0 1310-00349976.[3]
Database references
SIMBADdata
KICdata

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. It has a luminosity of 18.9 L☉,[10][9] a radius of 0.203 R☉, and a mass about half of that of the sun. The star was an evolutionary giant less than 20 million years ago.[10]

Kepler-70 is still fusing.[9][10] When it runs out of helium, it will contract into a white dwarf.[10]

Planetary system

On December 26, 2011, evidence for two extremely short-period planets, Kepler-70b and Kepler-70c, was announced by Charpinet et al.[6] 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[7] 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[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 has a temp of 7288 K,[10] the same as that of an F0 star.

The Kepler-70 planetary system
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 [note 2]° 0.759 R⊕
d (unconfirmed) — — — — — —
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.

References
  1. "Notes for Planet KOI-55 b". Extrasolar Planet Database. Archived from the original on 19 January 2012. Retrieved 1 January 2012.
  2. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  3. "KPD 1943+4058". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 1 January 2012.
  4. Sherrod, P. Clay; Koed, Thomas L. (2003), A Complete Manual of Amateur Astronomy: Tools and Techniques for Astronomical Observations, Astronomy Series, Courier Dover Publications, p. 9, ISBN 0-486-42820-6
  5. Cain, Fraser (4 February 2009). "White Dwarf Stars". Universe Today. Retrieved 8 January 2012.
  6. Charpinet, S.; et al. (December 21, 2011), "A compact system of small planets around a former red-giant star", Nature, 480 (7378): 496–499, Bibcode:2011Natur.480..496C, doi:10.1038/nature10631, PMID 22193103, S2CID 2213885
  7. Krzesinski, J. (August 25, 2015), "Planetary candidates around the pulsating sdB star KIC 5807616 considered doubtful", Astronomy & Astrophysics, 581: A7, Bibcode:2015A&A...581A...7K, doi:10.1051/0004-6361/201526346
  8. Blokesz, A.; Krzesinski, J.; Kedziora-Chudczer, L. (4 July 2019), "Analysis of putative exoplanetary signatures found in light curves of two sdBV stars observed by Kepler", Astronomy & Astrophysics, 627: A86, Bibcode:2019A&A...627A..86B, doi:10.1051/0004-6361/201835003, S2CID 182952925
  9. jamesrushford (2013-10-22). "Kepler 70b: The Coolest Exoplanet". PC 120: Life in the Universe. Retrieved 2021-07-27.
  10. jarrettkong (2013-10-23). "Kepler-70b: The Remnant of a Time Long Past". PC 120: Life in the Universe. Retrieved 2021-07-27.
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