Gliese 229

Gliese 229 (also written as Gl 229 or GJ 229) is a binary system composed of red dwarf and brown dwarf about 19 light years away in the constellation Lepus. The primary component has 58% of the mass of the Sun,[7] 69% of the Sun's radius,[8] and a very low projected rotation velocity of 1 km/s at the stellar equator.[10]

Gliese 229

Gliese 229 A and B.
Observation data
Epoch J2000      Equinox J2000
Constellation Lepus
Right ascension 06h 10m 34.6154s[1]
Declination −21° 51′ 52.715″[1]
Apparent magnitude (V) 8.14
Characteristics
Spectral type M1Ve/T7[2]
U−B color index +1.222[2]
B−V color index +1.478[2]
Variable type Flare star
Astrometry
Radial velocity (Rv)+3.9[3] km/s
Proper motion (μ) RA: –137.01[1] mas/yr
Dec.: –714.05[1] mas/yr
Parallax (π)173.81 ± 0.99[4] mas
Distance18.8 ± 0.1 ly
(5.75 ± 0.03 pc)
Absolute magnitude (MV)9.33[5]
Absolute bolometric
magnitude (Mbol)		7.96[6]
Details
Mass0.58/0.02[7] M☉
Radius0.69/0.047[8] R☉
Luminosity (bolometric)0.052[nb 1]/~0.000011 L☉
Luminosity (visual, LV)0.0158[nb 2] L☉
Temperature3,700[6]/950[9] K
Rotational velocity (v sin i)1[10] km/s
Other designations
BD-21°1377, HD 42581, HIP 29295, LHS 1827, NSV 2863, SAO 171334, TYC 5945- 765-1
Database references
A
B

The star is known to be a low activity flare star, which means it undergoes random increases in luminosity because of magnetic activity at the surface. The spectrum shows emission lines of calcium in the H and K bands. The emission of X-rays has been detected from the corona of this star.[11] These may be caused by magnetic loops interacting with the gas of the star's outer atmosphere. No large-scale star spot activity has been detected.[2]

The space velocity components of this star are U = +12, V = –11 and W = –12 km/s.[12] The orbit of this star through the Milky Way galaxy has an eccentricity of 0.07 and an orbital inclination of 0.005.[2]

Planetary system

A substellar companion was discovered in 1994 by Caltech astronomers Kulkarni, Tadashi Nakajima, Keith Matthews, and Rebecca Oppenheimer, and Johns Hopkins scientists Sam Durrance and David Golimowski. It was confirmed in 1995 as Gliese 229B,[13][14] one of the first two instances of clear evidence for a brown dwarf, along with Teide 1. Although too small to sustain hydrogen-burning nuclear fusion as in a main sequence star, with a mass of 21 to 52.4 times that of Jupiter (0.02 to 0.05 solar masses), it is still too massive to be a planet. As a brown dwarf, its core temperature is high enough to initiate the fusion of deuterium with a proton to form helium-3, but it is thought that it used up all its deuterium fuel long ago.[15] This object now has a surface temperature of 950 K.[9]

In March 2014, a super-Neptune mass planet candidate was announced in a much closer-in orbit around GJ 229.[16] Given the proximity to the Sun, the orbit of GJ 229Ab might be fully characterized by the Gaia space-astrometry mission or via direct imaging. In 2020, a super-Earth mass planet was discovered around GJ 229. GJ 229Ac orbits the star closer in than GJ 229Ab, it is located towards the outer edge but still well inside the star's habitable zone and in that sense quite similar to Mars in our own solar system.[17]

The Gliese 229 planetary system[17]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
Ac ≥7.93 M⊕ 0.339 122.005 0.29 — —
Ab ≥10.02 M⊕ 0.896 523.242 0.17 — —
B ≥1.62[lower-alpha 1] MJ 19.433 ~50000 0.03 13°+10
−12°		 0.468 RJ
  1. Minimum mass of GJ 229B as measured by radial velocity measurements is 1.62 Mj.[17] However, observations of GJ 229B suggest, that the system is viewed with a relative face-on orientation with an inclination of 13+10
    −12    .[18] If that is true and the planetary system is coplanar, then the real masses of all planets would be about 4.5 times more massive than the minimal mass derived from radial velocity measurements (2.6 up to 57 times of minimal mass, depending on the exact angle of inclination).

References
  1. Perryman, M. A. C.; et al. (1997). "The Hipparcos Catalogue". Astronomy and Astrophysics. 323: L49–L52. Bibcode:1997A&A...323L..49P.
  2. Byrne, P. B.; Doyle, J. G.; Menzies, J. W. (May 1, 1985). "Optical photometry and spectroscopy of the flare star Gliese 229 (=HD42581)". Monthly Notices of the Royal Astronomical Society. 214 (2): 119–130. Bibcode:1985MNRAS.214..119B. doi:10.1093/mnras/214.2.119.
  3. Evans, D. S. (June 20–24, 1966). "The Revision of the General Catalogue of Radial Velocities". In Batten, Alan Henry; Heard, John Frederick (eds.). Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30. University of Toronto: International Astronomical Union. Bibcode:1967IAUS...30...57E.
  4. Perryman; et al. (1997). "HIP 29295". The Hipparcos and Tycho Catalogues. Retrieved 2014-11-29.
  5. "The One Hundred Nearest Star Systems". RECONS. Georgia State University. January 1, 2012. Retrieved 2013-04-16.
  6. Morales, J. C.; Ribas, I.; Jordi, C. (February 2008). "The effect of activity on stellar temperatures and radii". Astronomy and Astrophysics. 478 (2): 507–512. arXiv:0711.3523. Bibcode:2008A&A...478..507M. doi:10.1051/0004-6361:20078324. S2CID 16238033. Data from CDS table J/A+A/478/507.
  7. Zechmeister, M.; Kürster, M.; Endl, M. (October 2009). "The M dwarf planet search programme at the ESO VLT + UVES. A search for terrestrial planets in the habitable zone of M dwarfs". Astronomy and Astrophysics. 505 (2): 859–871. arXiv:0908.0944. Bibcode:2009A&A...505..859Z. doi:10.1051/0004-6361/200912479. S2CID 16845441.
  8. White, Stephen M.; Jackson, Peter D.; Kundu, Mukul R. (December 1989). "A VLA survey of nearby flare stars". Astrophysical Journal Supplement Series. 71: 895–904. Bibcode:1989ApJS...71..895W. doi:10.1086/191401.
  9. Geißler, K.; Chauvin, G.; Sterzik, M. F. (March 2008). "Mid-infrared imaging of brown dwarfs in binary systems". Astronomy and Astrophysics. 480 (1): 193–198. arXiv:0712.1887. Bibcode:2008A&A...480..193G. doi:10.1051/0004-6361:20078229. S2CID 9331798.
  10. Reiners, A. (May 2007). "The narrowest M-dwarf line profiles and the rotation-activity connection at very slow rotation". Astronomy and Astrophysics. 467 (1): 259–268. arXiv:astro-ph/0702634. Bibcode:2007A&A...467..259R. doi:10.1051/0004-6361:20066991. S2CID 8672566.
  11. Schmitt JHMM; Fleming TA; Giampapa MS (September 1995). "The X-Ray View of the Low-Mass Stars in the Solar Neighborhood". Astrophys. J. 450 (9): 392–400. Bibcode:1995ApJ...450..392S. doi:10.1086/176149.
  12. Gliese, W. (1969). "Catalogue of Nearby Stars". Veröffentlichungen des Astronomischen Rechen-Instituts Heidelberg. 22: 1. Bibcode:1969VeARI..22....1G.
  13. "Astronomers Announce First Clear Evidence of a Brown Dwarf". Space Telescope Science Institute news release STScI-1995-48. November 29, 1995. Retrieved 24 September 2013.
  14. Oppenheimer, Ben R. (2014), "Companions of Stars: From Other Stars to Brown Dwarfs to Planets and the Discovery of the First Methane Brown Dwarf", in Joergens, Viki (ed.), 50 Years of Brown Dwarfs - From Prediction to Discovery to Forefront of Research, Astrophysics and Space Science Library, 401, Springer, pp. 81–111, arXiv:1404.4430, doi:10.1007/978-3-319-01162-2_6, ISBN 978-3-319-01162-2, S2CID 118304613
  15. J. Kelly Beatty; Carolyn Collins Petersen; Andrew Chaikin (1999). The New Solar System. Cambridge University Press.
  16. Tuomi, Mikko; et al. (2014). "Bayesian search for low-mass planets around nearby M dwarfs – Estimates for occurrence rate based on global detectability statistics". Monthly Notices of the Royal Astronomical Society. 441 (2): 1545. arXiv:1403.0430. Bibcode:2014MNRAS.441.1545T. doi:10.1093/mnras/stu358. S2CID 32965505.
  17. https://arxiv.org/abs/2001.02577 Search for Nearby Earth Analogs. II. detection of five new planets, eight planet candidates, and confirmation of three planets around nine nearby M dwarfs
  18. Brandt, Timothy D.; Dupuy, Trent J.; Bowler, Brendan P.; Gagliuffi, Daniella C. Bardalez; Faherty, Jacqueline; Brandt, G. Mirek; Michalik, Daniel (2020). "A Dynamical Mass of 70±5 Jupiter Masses for Gliese 229B, the First Imaged T Dwarf". Astronomical Journal. 160: 4. arXiv:1910.01652. doi:10.3847/1538-3881/abb45e. S2CID 222277091.

Notes
  1. Using the absolute bolometric magnitude of Gliese 229 A and the absolute bolometric magnitude of the Sun , the bolometric luminosity can be calculated by
  2. Using the absolute visual magnitude of Gliese 229 A and the absolute visual magnitude of the Sun , the visual luminosity can be calculated by
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