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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]
Astrometry
Proper motion (μ) RA: 7.217(29) mas/yr[1]
Dec.: −3.148(30) mas/yr[1]
Parallax (π)0.9086 ± 0.0247 mas[1]
Distance3,590 ± 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
Other designations
2MASS J19452546+4105339, KIC 5807616, KOI-55, UCAC2 46165657, 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 star about 3,600 light-years (1,100 parsecs) away in the constellation Cygnus, with an 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

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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]

Artist's impression of Kepler-70b

Planetary system

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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 Nature that announced the discovery of the two planets, Stephane Charpinet, the two planets "probably plunged deep into the star's envelope during the red giant phase, but survived."[12] However, this is not the first sighting of planets orbiting a post-red-giant star – a handful of 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

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  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

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  1. ^ a b c d Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. 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. ^ 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. ^ a b c 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. ^ a b 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. ^ a b 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, arXiv:1906.03321, Bibcode:2019A&A...627A..86B, doi:10.1051/0004-6361/201835003, 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. ^ Bear, E.; Soker, N. (26 March 2012), "A tidally destructed massive planet as the progenitor of the two light planets around the SDB star KIC 05807616", The Astrophysical Journal Letters, 749 (1): L14, arXiv:1202.1168, Bibcode:2012ApJ...749L..14B, doi:10.1088/2041-8205/749/1/L14, S2CID 119262095
  14. ^ Jones, K.; Morris, B. M.; et al. (October 2022). "The stable climate of KELT-9b". Astronomy & Astrophysics. 666: A118. arXiv:2208.04818. Bibcode:2022A&A...666A.118J. doi:10.1051/0004-6361/202243823.
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