Kepler-61

Kepler-61 is a K-type main-sequence star approximately 1,100 light years from Earth in the constellation Cygnus. It is located within the field of vision of the Kepler spacecraft, the satellite that NASA's Kepler Mission used to detect planets that may be transiting their stars. On April 24, 2013 it was announced that the star has an extrasolar planet (a super-Earth) orbiting in the inner edge of the habitable zone, named Kepler-61b.[2]

Kepler-61
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension  19h 41m 13.0818s[1]
Declination +42° 28′ 30.987″[1]
Apparent magnitude (V) 15
Characteristics
Evolutionary stage Main sequence
Spectral type K7V[2]
Astrometry
Proper motion (μ) RA: −2.255±0.076[1] mas/yr
Dec.: 10.482±0.090[1] mas/yr
Parallax (π)2.9565 ± 0.0436[1] mas
Distance1,100 ± 20 ly
(338 ± 5 pc)
Details
Mass0.635 ± 0.037[3] M☉
Radius0.62 ± 0.03[3] R☉
Luminosity0.08 L☉
Temperature4017 +49
−150[2] K
Metallicity [Fe/H]0.03 ± 0.14[3] dex
Rotation35.078±0.924 days[4]
Age>1[3] Gyr
Other designations
KIC 6960913, KOI-1361
Database references
SIMBADdata
Extrasolar Planets
Encyclopaedia		data

Nomenclature and history
The Kepler Space Telescope search volume, in the context of the Milky Way Galaxy.

Prior to Kepler observation, Kepler-61 had the 2MASS catalogue number 2MASS J19411308+422831. In the Kepler Input Catalog it has the designation of KIC 6960913, and when it was found to have transiting planet candidates it was given the Kepler object of interest number of KOI-1361.

Planetary candidates were detected around the star by NASA's Kepler Mission, a mission tasked with discovering planets in transit around their stars. The transit method that Kepler uses involves detecting dips in brightness in stars. These dips in brightness can be interpreted as planets whose orbits pass in front of their stars from the perspective of Earth, although other phenomenon can also be responsible which is why the term planetary candidate is used.[5]

Following the acceptance of the discovery paper, the Kepler team provided an additional moniker for the system of "Kepler-61".[6] The discoverers referred to the star as Kepler-61, which is the normal procedure for naming the exoplanets discovered by the spacecraft.[2] Hence, this is the name used by the public to refer to the star and its planet.

Candidate planets that are associated with stars studied by the Kepler Mission are assigned the designations ".01" etc. after the star's name, in the order of discovery.[7] If planet candidates are detected simultaneously, then the ordering follows the order of orbital periods from shortest to longest.[7] Following these rules, there was only one candidate planet were detected, with an orbital period of 59.87756 days.

The designation b, derive from the order of discovery. The designation of b is given to the first planet orbiting a given star, followed by the other lowercase letters of the alphabet.[8] In the case of Kepler-61, there was only one planet detected, so only the letter b is used. The name Kepler-61 derives directly from the fact that the star is the catalogued 61st star discovered by Kepler to have confirmed planets.

Stellar characteristics

Kepler-61 is a K-type main sequence star that is approximately 63% the mass of and 62% the radius of the Sun. It has a temperature of 4017 K and is about 1 billion years old.[3] In comparison, the Sun is about 4.6 billion years old[9] and has a temperature of 5778 K.[10]

The star is a bit more rich in metals then the Sun, with a metallicity ([Fe/H]) of about 0.03, or about 107% of the amount of iron and other heavier metals found in the Sun.[3] The star's luminosity is somewhat normal for a star like Kepler-61, with a luminosity of around 8% of that of the solar luminosity.

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 15. Therefore, it is too dim to be seen with the naked eye.

Planetary system
The Kepler-61 planetary system[2]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 6.65 M⊕ 0.26 59.87756 <0.25 >89.80° 2.15 ± 0.13 R⊕

The only known planet transits the star; this means that the planet's orbit appear to cross in front of their star as viewed from the Earth's perspective. Its inclination relative to Earth's line of sight, or how far above or below the plane of sight they are, vary by less than one degree. This allows direct measurements of the planet's periods and relative diameters (compared to the host star) by monitoring the planet's transit of the star.

Kepler-61b is a super-Earth with a radius 2.15 times that of Earth, and orbits near the inner edge of the habitable zone. It has an eccentric orbit that takes it in and out and thus experiences temperature swings, which may hinder its habitability. Also because of its radius, it may be a mini-Neptune, without a solid surface.

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See also
  • Kepler Mission
  • List of planetary systems

References
  1. 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.
  2. Exoplanet Characterization by Proxy: a Transiting 2.15 R_Earth Planet Near the Habitable Zone of the Late K dwarf Kepler-61 Sarah Ballard, David Charbonneau, Francois Fressin, Guillermo Torres, Jonathan Irwin, Jean-Michel Desert, Elisabeth Newton, Andrew W. Mann, David R. Ciardi, Justin R. Crepp, Christopher E. Henze, Stephen T. Bryson, Steven B. Howell, Elliott P. Horch, Mark E. Everett, Avi Shporer et al. April 26, 2013
  3. "Kepler-61b". Retrieved July 20, 2016.
  4. 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.
  5. Morton, Timothy; Johnson, John (23 August 2011). "On the Low False Positive Probabilities of Kepler Planet Candidates". The Astrophysical Journal. 738 (2): 170. arXiv:1101.5630. Bibcode:2011ApJ...738..170M. doi:10.1088/0004-637X/738/2/170.
  6. NASA (27 January 2014). "Kepler – Discoveries – Summary Table". NASA. Retrieved 1 March 2014.
  7. "Kepler Input Catalog search result". Space Telescope Science Institute. Retrieved 25 July 2015.
  8. Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  9. Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011.
  10. Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.

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