Kepler-186

Kepler-186 is a main-sequence M1-type dwarf star, located 178.5 parsecs (582 light years) away in the constellation of Cygnus. The star is slightly cooler than the sun, with roughly half its metallicity. It is known to have five planets, including the first Earth-sized world discovered in the habitable zone: Kepler-186f.[7] The star hosts four other planets discovered so far, though Kepler-186 b, c, and d are too close, but e is near the habitable zone's inner edge.

Kepler-186[1]

Kepler-186 is indicated by the red circle
(2MASS J band image)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cygnus
Right ascension  19h 54m 36.6536s[2]
Declination +43° 57′ 18.0259″[2]
Apparent magnitude (V) 15.29[3]
Characteristics
Spectral type M1V[4]
Astrometry
Proper motion (μ) RA: 2.099±0.041[2] mas/yr
Dec.: −4.361±0.042[2] mas/yr
Parallax (π)5.6020 ± 0.0244[2] mas
Distance579.23[5] ly
(177.59[5] pc)
Details
Mass0.544 ± 0.02[4] M☉
Radius0.523 ± 0.02[4] R☉
Luminosity (bolometric)0.055 +0.011
−0.006[4] L☉
Temperature3755 ± 90[4] K
Metallicity [Fe/H]−0.26 ± 0.12[4] dex
Rotation34.404±0.075 days[6]
Age4.0 ± 0.6[4] Gyr
Other designations
KIC 8120608, KOI-571,
2MASS J19543665+4357180
Database references
SIMBADdata

Star

A number of previously unknown measurements of the star are known.[8][9] In the infrared/microwave EM spectrum[1] its H band magnitude is 11.605, J band magnitude is 12.473, and its K band magnitude is 11.605. In the visual Photometric system magnitude it is 14.90(R)(towards the red end of the visual spectrum) and 16.40(B)(the blue end of the spectrum)[8] (see also Apparent magnitude.) It is a BY Draconis variable changing brightness slightly, probably from starspots, with a period of 33.695 days.[10]

The star is Red dwarf/M-class bordering on being an Orange dwarf/K-class star, with a mass nearly half that of the Sun's, with a density ~1.59 x 105 kg/m3.

Discovery of a planetary system

Within two first years of gathered data, the signals of four inner planetary candidates were found. Discussion of planets in the system was taking place in August and November 2013.[11] In February 2014, those planets were confirmed through the "verification by multiplicity" method. The fifth outermost candidate was confirmed in the same manner in April 2014.[12] The possibility that the signals in the light curve of the star were actually from something else has been ruled out by an investigation with the W. M. Keck and Gemini Observatories, using speckle imaging and adaptive optics techniques, which, while unable to resolve the planets, were able to rule out other possibilities than the system of planets.[13]

Planetary system
The Kepler-186 planetary system
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b — 0.0378 3.8867907 <0.24 83.65° 1.08 R⊕
c — 0.0574 7.267302 <0.24 85.94° 1.25 R⊕
d — 0.0861 13.342996 <0.25 87.09° 1.39 R⊕
e ~2.29 M⊕ 0.1216 22.407704 <0.24 88.24° 1.33 R⊕
f ~1.4 M⊕ 0.432 129.9444 <0.04 89.9° 1.17 R⊕

The five planets discovered around Kepler-186 are all expected to have a solid surface. The smallest one, Kepler-186b, is only 8% larger than Earth, while the largest one, Kepler-186d, is almost 40% larger.

The four innermost planets are probably tidally locked, but Kepler-186f is further out, where the star's tidal effects are much weaker, so there may not have been enough time for its spin to slow down that much. Because of the very slow evolution of red dwarf stars, the age of the Kepler-186 system is poorly constrained, although it is likely to be greater than a few billion years.[14] There is a roughly 50-50 chance it is tidally locked. Since it is closer to its star than Earth is to the Sun, it will probably rotate much more slowly than Earth; its day could be weeks or months long (see Tidal effects on rotation rate, axial tilt and orbit).[15]

Planetary formation simulations have also shown that there could be one additional non-transiting low-mass planet between Kepler-186e and Kepler-186f. If this planet exists, it is likely not much more massive than Earth. If it were, its gravitational influence would likely prevent Kepler-186f from transiting.[14] Conjectures involving the Titius–Bode law, (and the related Dermott's law) indicate that there could be several remaining planets to be found in the system - two small ones between e and f and another larger one outside of f.[16]

The low metallicity of the star at a metallicity (dex) of -0.26, or to put it another way, about half that of the Sun's,[7] is associated with a decreased chance of planets overall and giant planets specifically but an increased chance of Earth sized planets, in a general study of stars.[17]

Naming

Kepler project

As the Kepler telescope observational campaign progressed initial identifications of systems were entered in the Kepler Input Catalog (KIC), and then progressed as a candidate host of planets as Kepler Object of Interest (KOI). Thus Kepler 186 started as KIC 8120608 and then was identified as KOI 571.[18]

Outside the Kepler project

Outside of the Kepler project, the 2MASS survey catalogued this star as 2MASS J19543665+4357180.[1]

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See also

References
  1. SIMBAD, KIC8120608
  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. Souto, Diogo; et al. (2017). "Chemical Abundances of M-dwarfs from the APOGEE Survey. I. The Exoplanet Hosting Stars Kepler-138 and Kepler-186". The Astrophysical Journal. 835 (2): 239. arXiv:1612.01598. Bibcode:2017ApJ...835..239S. doi:10.3847/1538-4357/835/2/239.
  4. "Kepler-186 f". NASA Exoplanet Archive. Retrieved 19 July 2016.
  5. Bailer-Jones, C. A. L.; et al. (August 2018). "Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2". The Astronomical Journal. 156 (2): 58. arXiv:1804.10121. Bibcode:2018AJ....156...58B. doi:10.3847/1538-3881/aacb21. Distance to Kepler 186, after taking into account light extinction
  6. McQuillan, A.; Mazeh, T.; Aigrain, S. (2013). "Stellar Rotation Periods of The Kepler objects of Interest: A Dearth of Close-In Planets Around Fast Rotators". The Astrophysical Journal Letters. 775 (1). L11. arXiv:1308.1845. Bibcode:2013ApJ...775L..11M. doi:10.1088/2041-8205/775/1/L11.
  7. Quintana, E. V.; Barclay, T.; Raymond, S. N.; Rowe, J. F.; Bolmont, E.; Caldwell, D. A.; Howell, S. B.; Kane, S. R.; Huber, D.; Crepp, J. R.; Lissauer, J. J.; Ciardi, D. R.; Coughlin, J. L.; Everett, M. E.; Henze, C. E.; Horch, E.; Isaacson, H.; Ford, E. B.; Adams, F. C.; Still, M.; Hunter, R. C.; Quarles, B.; Selsis, F. (2014-04-18). "An Earth-Sized Planet in the Habitable Zone of a Cool Star". Science. 344 (6181): 277–280. arXiv:1404.5667. Bibcode:2014Sci...344..277Q. doi:10.1126/science.1249403. PMID 24744370. free version = http://www.nasa.gov/sites/default/files/files/kepler186_main_final.pdf
  8. VizieR Detailed Page for 2MASS 19543665+4357180, "This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation."
  9. VizieR Detailed Page, KIC 8120608, Kepler Input Catalog (Kepler Mission Team, 2009)
  10. "KIC 8120608". The International Variable Star Index, Version 1.1 [C]. American Association of Variable Star Observers (AAVSO). Retrieved April 19, 2014.
  11. Glister, Paul (5 November 2013). "Earth-Sized Planets in Habitable Zone Common". Centauri Dreams. Archived from the original on 19 April 2014. See comment by "Holger 16 November 2013 at 14:21".
    ^ redakce ["editor"] (6 August 2013). "Kepler (asi) našel obyvatelnou planetu o velikosti Země" [Kepler (probably) found a habitable planet the size of Earth] (in Czech). exoplanety.cz. Archived from the original on 20 August 2013.
    ^ "Kepler: Erster Kandidat einer habitablen Exoerde Veröffentlicht" [Kepler: First candidate of a habitable Exoplanet Published]. Zauber der Sterne [Magic of the stars] (in German). 19 August 2013. Archived from the original on 27 September 2013.
    ^ Bovaird, Timothy; Lineweaver, Charles H. (2013). "Exoplanet Predictions Based on the Generalised Titius-Bode Relation". Monthly Notices of the Royal Astronomical Society. 435 (2): 14–15. arXiv:1304.3341. Bibcode:2013MNRAS.435.1126B. doi:10.1093/mnras/stt1357.
  12. Wall, Mike (26 February 2014). "Population of Known Alien Planets Nearly Doubles as NASA Discovers 715 New Worlds". Space.com. Retrieved 26 February 2014.
  13. Elisa Quintana; Steve Howell (Apr 17, 2014). "First potentially habitable Earth-sized planet confirmed by Gemini and Keck Observatories". Press Release. Gemini Observatory. Retrieved April 23, 2014.
  14. Formation, tidal evolution and habitability of the Kepler-186 system, Emeline Bolmont, Sean N. Raymond, Philip von Paris, Franck Selsis, Franck Hersant, Elisa V. Quintana, Thomas Barclay, (Submitted on 16 Apr 2014)
  15. Staff. "Kepler 186f - A Planet in the Habitable Zone (video)". Hangout On-Air. SETI Institute. Archived from the original on 2014-04-18. Retrieved 2014-04-18.
  16. Bovaird, Timothy; Lineweaver, Charles H. (2013). "Exoplanet Predictions Based on the Generalised Titius-Bode Relation". Monthly Notices of the Royal Astronomical Society. 435 (2): 14–15. arXiv:1304.3341. Bibcode:2013MNRAS.435.1126B. doi:10.1093/mnras/stt1357.
  17. J. S. Greaves; D. A. Fischer; M. C. Wyatt (November 10, 2005). "Metallicity, debris discs and planets" (PDF). Monthly Notices of the Royal Astronomical Society. 366 (1): 283–286. Bibcode:2006MNRAS.366..283G. doi:10.1111/j.1365-2966.2005.09848.x. ISSN 1365-2966. Retrieved April 20, 2014.
  18. Rowe, Jason F.; et al. (2014). "Validation of Kepler's Multiple Planet Candidates. III: Light Curve Analysis & Announcement of Hundreds of New Multi-planet Systems (Revision 8.0)". The Astrophysical Journal. 784 (1): 45. arXiv:1402.6534. Bibcode:2014ApJ...784...45R. doi:10.1088/0004-637X/784/1/45.
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