Kepler-186

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Kepler-186 [1]
Kepler-186.svg
Kepler-186 is indicated by the red circle
(2MASS J band image)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cygnus
Right ascension 19h 54m 36.651s[1]
Declination +43° 57′ 18.06″[1]
Apparent magnitude (V) ~+15.65
Characteristics
Spectral type M1V
Details
Mass 0.48 M☉
Radius 0.47 R☉
Luminosity 0.0412[2] L☉
Temperature 3788 K
Metallicity [Fe/H] -0.28 dex
Other designations
KIC 8120608, KOI-571,
2MASS J19543665+4357180

Kepler-186 is a main-sequence M1-type dwarf star, located 151 ± 18 parsecs (492 ± 59 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.[2] 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.

Star

A number of previously unknown measurements of the star are known.[3][4] 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)[3] (see also Apparent magnitude.) It is a BY Draconis variable changing brightness slightly, probably from starspots, with a period of 33.695 days.[5]

The star is a 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.[6] 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.[7] 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.[8]

Planetary system

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.[9] 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).[10]

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.[9] 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.[11]

Low metallicity of the star, at -.28 relative to the Sun or put another way about half that of the Sun,[2] 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.[12]

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 — 0.1216 22.407704 <0.24 88.24° 1.33 R⊕
f — 0.3926 129.9459 <0.34 89.9° 1.11 R⊕

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.[13]

Outside the Kepler project

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

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 SIMBAD, KIC8120608
  2. ↑ 2.0 2.1 2.2 Lua error in package.lua at line 80: module 'strict' not found. free version = http://www.nasa.gov/sites/default/files/files/kepler186_main_final.pdf
  3. ↑ 3.0 3.1 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."
  4. ↑ VizieR Detailed Page, KIC 8120608, Kepler Input Catalog (Kepler Mission Team, 2009)
  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found. See comment by "Holger 16 November 2013 at 14:21".
    ^ Lua error in package.lua at line 80: module 'strict' not found.
    ^ Lua error in package.lua at line 80: module 'strict' not found.
    ^ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ 9.0 9.1 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)
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ Lua error in package.lua at line 80: module 'strict' not found.

External links

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