Gliese 667

Gliese 667 (142 G. Scorpii) is a triple-star system in the constellation Scorpius lying at a distance of about 6.8 pc (23.6 ly) from Earth. All three of the stars have masses smaller than the Sun. There is a 12th magnitude star close to the other three, but it is not gravitationally bound to the system. To the naked eye, the system appears to be a single faint star of magnitude 5.89.

Gliese 667 A/B/C
A star chart of the constellation of Scorpius showing the position of Gliese 667
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension 17h 18m 57.16483s[1]
Declination −34° 59′ 23.1416″[1]
Apparent magnitude (V) 5.91/7.20/10.20[2]
Characteristics
Spectral type K3V + K5V + M1.5V[2][3]
U−B color index 0.83/???/1.17
B−V color index 1.03/???/1.57
Variable type A: suspected
B: unknown
C: flare star
Astrometry
Radial velocity (Rv)6.5[4] km/s
Proper motion (μ) RA: 1129.76[1] mas/yr
Dec.: −77.02[1] mas/yr
Parallax (π)140.88 ± 2.04[5] mas
Distance23.2 ± 0.3 ly
(7.1 ± 0.1 pc)
Absolute magnitude (MV)7.07/8.02/11.03
Details
GJ 667 AB
Mass0.73 / 0.69[6] M☉
Radius0.76 / 0.70[2] R☉
Metallicity [Fe/H]–0.59[7] dex
GJ 667 C
Mass0.31[4] M☉
Radius0.42[2] R☉
Luminosity0.0137[4] L☉
Temperature3,700 ± 100[4] K
Metallicity [Fe/H]–0.59 ± 0.10[4] dex
Rotation105 days [4]
Age2–10[4] Gyr
Orbit[8]
CompanionGliese 667 B
Period (P)42.15 yr
Semi-major axis (a)1.81″
Eccentricity (e)0.58
Inclination (i)128°
Longitude of the node (Ω)313°
Periastron epoch (T)1975.9
Argument of periastron (ω)
(secondary)		247°
Other designations
142 G. Scorpii, CD−34°11626, GJ 667, HD 156384, HIP 84709, HR 6426, LHS 442/442/443, SAO 208670.
Database references
SIMBADThe system
AB
A
B
C
Cb
Cc
Ce
Cf
Exoplanet ArchiveGliese 667 C
ARICNSGliese 667 A
B
C
Extrasolar Planets
Encyclopaedia		data

The system has a relatively high proper motion, exceeding 1 second of arc per year.

The two brightest stars in this system, GJ 667 A and GJ 667 B, are orbiting each other at an average angular separation of 1.81 arcseconds with a high eccentricity of 0.58. At the estimated distance of this system, this is equivalent to a physical separation of about 12.6 AU, or nearly 13 times the separation of the Earth from the Sun. Their eccentric orbit brings the pair as close as about 5 AU to each other, or as distant as 20 AU, corresponding to an eccentricity of 0.6.[note 1][9] This orbit takes approximately 42.15 years to complete and the orbital plane is inclined at an angle of 128° to the line of sight from the Earth. The third star, GJ 667 C, orbits the GJ 667 AB pair at an angular separation of about 30", which equates to a minimum separation of 230 AU.[4][10] GJ 667 C also has a system of two confirmed super-Earths and five additional candidates, though the innermost, GJ 667 Cb, may be a gas dwarf; GJ 667 Cc, and the controversial Cf and Ce, are in the circumstellar habitable zone.

Gliese 667 AB

The largest star in the system, Gliese 667 A (GJ 667 A), is a K-type main-sequence star of stellar classification K3V.[2] It has about 73%[6] of the mass of the Sun and 76%[2] of the Sun's radius, but is radiating only around 12-13% of the luminosity of the Sun.[11] The concentration of elements other than hydrogen and helium, what astronomers term the star's metallicity, is much lower than in the Sun with a relative abundance of around 26% solar.[7] The apparent visual magnitude of this star is 6.29, which, at the star's estimated distance, gives an absolute magnitude of around 7.07 (assuming negligible extinction from interstellar matter).

Like the primary, the secondary star Gliese 667 B (GJ 667 B) is a K-type main-sequence star, although it has a slightly later stellar classification of K5V. This star has a mass of about 69%[6] of the Sun, or 95% of the primary's mass, and it is radiating about 5% of the Sun's visual luminosity. The secondary's apparent magnitude is 7.24, giving it an absolute magnitude of around 8.02.

Gliese 667 C

Gliese 667 C is the smallest star in the system, with only around 31%[6] of the mass of the Sun and 42%[2] of the Sun's radius, orbiting approximately 230 AU from the Gliese 667 AB pair.[12] It is a red dwarf with a stellar classification of M1.5. This star is radiating only 1.4% of the Sun's luminosity from its outer atmosphere at a relatively cool effective temperature of 3,700 K.[4] This temperature is what gives it the red-hued glow that is a characteristic of M-type stars.[13] The apparent magnitude of the star is 10.25, giving it an absolute magnitude of about 11.03. It is known to have a system of two planets; claims have been made for five additional planets[14] but this may be an error due to failure to account for correlated noise in the radial velocity data.[15][16] The red dwarf status of the star would allow planet Cc, which is in the habitable zone, to receive minimal amounts of ultraviolet radiation.[12]

Planetary system
Artist's impression of Gliese 667 Cb with the Gliese 667 A/B binary in the background
An artist's impression of GJ 667 Cc, a potentially habitable planet orbiting a red dwarf constituent in a trinary star system
Artist's impression of the view from the exoplanet Gliese 667 Cd looking towards the planet’s parent star (Gliese 667C)

Two extrasolar planets, Gliese 667 Cb (GJ 667 Cb) and Cc, have been confirmed orbiting Gliese 667 C by radial velocity measurements of GJ 667.[15][16] There were also though to be five other potential additional planets,[4][14] however it was later shown that they may be artifacts resulting from correlated noise.[15][16] Tuomi et al. 2019 detect planets b, c, and d, but do not detect any of the other claimed planets;[17] however, the NASA Exoplanet Archive considers planet d disproven.[18]

Planet Cb was first announced by the European Southern Observatory's HARPS group on 19 October 2009. The announcement was made together with 29 other planets, while Cc was first mentioned by the same group in a pre-print made public on 21 November 2011.[19] Announcement of a refereed journal report came on 2 February 2012 by researchers at the University of Göttingen/Carnegie Institution for Science.[4][20] In this announcement, GJ 667 Cc was described as one of the best candidates yet found to harbor liquid water, and thus, potentially, support life on its surface.[21] A detailed orbital analysis and refined orbital parameters for Gliese 667 Cc were presented.[4] Based on GJ 667 C's bolometric luminosity, GJ 667 Cc would receive 90% of the light Earth does,[11] however much of that electromagnetic radiation would be in the invisible infrared light part of the spectrum. Based on black body temperature calculation, GJ 667 Cc should absorb more overall electromagnetic radiation, making it warmer (277.4 K) and placing it slightly closer to the "hot" edge of the habitable zone than Earth (254.3 K).

From the surface of Gliese 667 Cc, the second confirmed planet out that orbits along the middle of the habitable zone, Gliese 667 C would have an angular diameter of 1.24 degrees–2.3 times[note 2] larger than our Sun appears from the surface of the Earth, covering 5.4 times more area–but would still only occupy 0.003 percent of Gliese 667 Cc's sky sphere or 0.006 percent of the visible sky when directly overhead.

At one point, five additional planets were thought to exist in the system, with three of them thought to be relatively certain to exist. However, subsequent studies showed that the other planets in the system could possibly be artifacts of noise and stellar activity, cutting the minimum number of planets down to two. The analysis did find some evidence for the third planet, Gliese 667 Cd, but was unable to confirm it.[15] A later study also detected the third planet, but the study in question has not been published yet or peer-reviewed.[17]

The Gliese 667 C planetary system[22][16]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b ≥5.6±0.3 M⊕ 0.050431±0.000004 7.1999±0.0009 0.15±0.05 — —
c ≥4.1±0.6 M⊕ 0.12501±0.00009 28.10±0.03 0.27±0.1 — —
d (unconfirmed) ≥5.1+1.8
−1.7 M⊕		 0.28+0.02
−0.03		 91.6+0.8
−0.9		 0.03+0.2
−0.03		 — —

References
  1. van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600
  2. Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics", Astronomy and Astrophysics, 367 (2): 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451, S2CID 425754 Note: see VizieR catalogue J/A+A/367/521.
  3. Suárez Mascareño, A.; et al. (September 2015), "Rotation periods of late-type dwarf stars from time series high-resolution spectroscopy of chromospheric indicators", Monthly Notices of the Royal Astronomical Society, 452 (3): 2745–2756, arXiv:1506.08039, Bibcode:2015MNRAS.452.2745S, doi:10.1093/mnras/stv1441, S2CID 119181646.
  4. Anglada-Escudé, Guillem; Arriagada, Pamela; Vogt, Steven S.; Rivera, Eugenio J.; Butler, R. Paul; Crane, Jeffrey D.; Shectman, Stephen A.; Thompson, Ian B.; Minniti, Dante; Haghighipour, Nader; Carter, Brad D.; Tinney, C. G.; Wittenmyer, Robert A.; Bailey, Jeremy A.; O'Toole, Simon J.; Jones, Hugh R. A.; Jenkins, James S. (2012). "A Planetary System around the nearby M Dwarf GJ 667C with At Least One Super-Earth in Its Habitable Zone". The Astrophysical Journal Letters. 751 (1). L16. arXiv:1202.0446. Bibcode:2012ApJ...751L..16A. doi:10.1088/2041-8205/751/1/L16. S2CID 16531923.
  5. Lurie, John C.; Henry, Todd J.; Jao, Wei-Chun; Quinn, Samuel N.; Winters, Jennifer G.; Ianna, Philip A.; Koerner, David W.; Riedel, Adric R.; Subasavage, John P. (2014). "The Solar Neighborhood. XXXIV. a Search for Planets Orbiting Nearby M Dwarfs Using Astrometry". The Astronomical Journal. 148 (5): 91. arXiv:1407.4820. Bibcode:2014AJ....148...91L. doi:10.1088/0004-6256/148/5/91. S2CID 118492541.
  6. Tokovinin, A. (September 2008), "Comparative statistics and origin of triple and quadruple stars", Monthly Notices of the Royal Astronomical Society, 389 (2): 925–938, arXiv:0806.3263, Bibcode:2008MNRAS.389..925T, doi:10.1111/j.1365-2966.2008.13613.x, S2CID 16452670
  7. Cayrel de Strobel, G.; Soubiran, C.; Ralite, N. (July 2001), "Catalogue of [Fe/H] determinations for FGK stars: 2001 edition", Astronomy and Astrophysics, 373: 159–163, arXiv:astro-ph/0106438, Bibcode:2001A&A...373..159C, doi:10.1051/0004-6361:20010525, S2CID 17519049
  8. Söderhjelm, Staffan (January 1999), "Visual binary orbits and masses POST HIPPARCOS", Astronomy and Astrophysics, 341: 121–140, Bibcode:1999A&A...341..121S
  9. Bowman, Richard L. "Interactive Planetary Orbits - Kepler's Laws Calculations". Archived from the original on 12 December 2012. Retrieved 23 February 2012.
  10. Philip C. Gregory (2012). "Additional Keplerian Signals in the HARPS data for Gliese 667C from a Bayesian Re-analysis". arXiv:1212.4058 [astro-ph.EP].
  11. Sven Wedemeyer. "Life on Gliese 667Cc?". Institute of Theoretical Astrophysics. Archived from the original on 2013-07-03. Retrieved 2012-12-28.
  12. Anglada-Escudé, Guillem; Tuomi, Mikko; Gerlach, Enrico; Barnes, Rory; Heller, René; Jenkins, James S.; Wende, Sebastian; Vogt, Steven S.; Butler, R. Paul; Reiners, Ansgar; Jones, Hugh R. A. (2013-06-07). "A dynamically-packed planetary system around GJ 667C with three super-Earths in its habitable zone" (PDF). Astronomy & Astrophysics. 556: A126. arXiv:1306.6074. Bibcode:2013A&A...556A.126A. doi:10.1051/0004-6361/201321331. S2CID 14559800. Archived from the original (PDF) on 2013-06-30. Retrieved 2013-06-25.
  13. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-18, retrieved 2012-01-16
  14. Anglada-Escudé, Guillem; Tuomi, Mikko; Gerlach, Enrico; Barnes, Rory; Heller, René; Jenkins, James S.; Wende, Sebastian; Vogt, Steven S.; Butler, R. Paul; Reiners, Ansgar; Jones, Hugh R. A. (2013-06-07). "A dynamically-packed planetary system around GJ 667C with three super-Earths in its habitable zone" (PDF). Astronomy & Astrophysics. 556: A126. arXiv:1306.6074. Bibcode:2013A&A...556A.126A. doi:10.1051/0004-6361/201321331. S2CID 14559800. Retrieved 2013-06-25.
  15. Feroz, F.; Hobson, M. P. (2014). "Bayesian analysis of radial velocity data of GJ667C with correlated noise: evidence for only two planets". Monthly Notices of the Royal Astronomical Society. 437 (4): 3540–3549. arXiv:1307.6984. Bibcode:2014MNRAS.437.3540F. doi:10.1093/mnras/stt2148. S2CID 119287992.
  16. Robertson, Paul; Mahadevan, Suvrath (October 2014). "Disentangling Planets and Stellar Activity for Gliese 667C". The Astrophysical Journal . 793 (2): L24. arXiv:1409.0021. Bibcode:2014ApJ...793L..24R. doi:10.1088/2041-8205/793/2/L24. S2CID 118404871.
  17. Tuomi, M.; et al. (11 June 2019). "Frequency of planets orbiting M dwarfs in the Solar neighbourhood". arXiv:1906.04644 [astro-ph.EP].
  18. "Targets Excluded from the Archive". NASA Exoplanet Archive. Retrieved 27 September 2020.
  19. Bonfils, X.; et al. (November 2011), "The HARPS search for southern extra-solar planets XXXI. The M-dwarf sample", Astronomy and Astrophysics, submitted: A109, arXiv:1111.5019, Bibcode:2013A&A...549A.109B, doi:10.1051/0004-6361/201014704, S2CID 119288366
  20. University of Göttingen. Presseinformation: Wissenschaftler entdecken möglicherweise bewohnbare Super-Erde - Göttinger Astrophysiker untersucht Planeten in 22 Lichtjahren Entfernung. Nr. 17/2012 - 02.02.2012. Announcement on university homepage, retrieved 2012-02-02
  21. Chow, Denise (February 2, 2012). "Newfound Alien Planet is Best Candidate Yet to Support Life, Scientists Say". Space.com. Retrieved February 3, 2012.
  22. https://www.drewexmachina.com/2014/09/07/habitable-planet-reality-check-gj-667c/

Notes
  1. Based on a calculated eccentricity value of .
  2. . where is the angular diameter of the star from the surface of the planet in orbit (GJ667Cc in this case), is the angular diameter of the Sun (sol) from the surface of Earth, is the effective temperature of the Sun (sol), the effective temperature of the star, is the luminosity of the star as a fraction of the sun's luminosity and is the distance of the planet from the star in AU. This formula has been used as the luminosity and surface temperature published do not agree with the published radius. If you calculate the radius from the formula radius=sqrt(luminosity)/temp^2 (with all units given in multiples of the sun's values), you will see that the luminosity and temperature give a radius of 0.286 times the radius of the sun, not the same figure published in the literature. If you calculate the angular diameter in the sky using a trigonometric formula (atan(distance/radius)*2), the angular diameter derived using this revised radius agrees with the figures given here, by the shortcut formula above, which essentially makes the same calculation.

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