Gliese 180

Gliese  180 (often shortened to GJ 180), is a small red dwarf star in the equatorial constellation of Eridanus. It is invisible to the naked eye with an apparent visual magnitude of 10.9.[2] The star is located at a distance of 39 light years from the Sun based on parallax,[1] and is drifting closer with a radial velocity of −14.6 km/s.[5] It has a high proper motion, traversing the sky at the rate of 0.765 arcseconds per year.[10]

Gliese 180
A star chart of the constellation of Eridanus showing the position of Gliese 180
Observation data
Epoch J2000      Equinox J2000
Constellation Eridanus
Right ascension 04h 53m 49.9798s[1]
Declination −17° 46′ 24.294″[1]
Apparent magnitude (V) 10.894[2]
Characteristics
Spectral type M2V[3] or M3V[4]
U−B color index 1.155[2]
B−V color index 1.549[2]
V−R color index 1.018[2]
R−I color index 1.205[2]
J−H color index 0.553[2]
J−K color index 0.815[2]
Astrometry
Radial velocity (Rv)−14.55±0.24[5] km/s
Proper motion (μ) RA: 408.571[1] mas/yr
Dec.: −644.464[1] mas/yr
Parallax (π)83.7182 ± 0.0313[1] mas
Distance38.96 ± 0.01 ly
(11.945 ± 0.004 pc)
Absolute magnitude (MV)10.48[2]
Details
Mass0.4316±0.0050[3] M☉
Radius0.4229±0.0047[3] R☉
Luminosity0.02427±0.00036[3] L☉
Surface gravity (log g)4.73+0.05
−0.07[6] cgs
Temperature3,634+57
−40[6] K
Metallicity [Fe/H]−0.12±0.16[3] dex
Rotation65 days[7]
Rotational velocity (v sin i)3.4+1.9
−0.8[6] km/s
Age5.0[8] Gyr
Other designations
GJ 180, HIP 22762, L 736-30, LFT 377, LHS 1712, LP 776-27, LPM 198, LTT 2116, NLTT 14144, PLX 1097, TYC 5903-680-1, 2MASS J04534995-1746235,[9] [RHG95] 838
Database references
SIMBADdata
Exoplanet Archivedata
ARICNSdata

The stellar classification of GJ 180 is catalogued as M2V[3] or M3V,[4] depending on the study, which indicates this is a dim red dwarf – an M-type main-sequence star that is generating energy by core hydrogen fusion. Reiners and associates (2012) do not consider it to be active star.[11] It is about five[8] billion years old and is spinning with a projected rotational velocity of ~3 km/s,[6] giving it a rotation period of about 65 days.[7] The star has 43% of the Sun's mass and 42% of the radius of the Sun. It is radiating just 2.4%[3] of the luminosity of the Sun from its photosphere at an effective temperature of 3,634 K.[6]

Planetary system

Gliese 180 is known to have three exoplanets designated Gliese 180 b, Gliese 180 c and Gliese 180 d,[9] by order of distance from the star. The components 'b' anc 'c' are super Earths with an orbital period ratio of 7:5, which suggests a mean motion resonance that is stabilizing the orbits. The habitable zone of this star, by the criteria of Kopparapu and associates (2013), ranges from 0.12 AU out to 0.24 AU, which thus includes object 'c'.[12]

According to the Planetary Habitability Laboratory (PHL) in Puerto Rico, both b and c worlds in the system may be classifiable as potentially habitable planets. Planet Gliese 180 b and Gliese 180 c have masses of 6.4 and 8.3 Earth masses, respectively.[13] However, Dr Mikko Tuomi, of the UK's University of Hertfordshire, whose team identified the planets, disagreed, stating:

"The PHL adds some sort of an “extended HZ”, which I, frankly, do not know how it’s calculated, but that adds some areas of potential habitability to the inner and outer edges of the HZ as we have defined it. They included the inner companion of the GJ 180 system (planet b) that we consider too hot to be potentially habitable.”[13]
The Gliese 180 planetary system[14][15][16]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 0.02611 ± 0.00558 MJ 0.103 ± 0.0008 17.38 ± 0.016 0.11 ± 0.03 — —
с 0.02014 ± 0.00126 MJ 0.129 ± 0.01 24.329 ± 0.014 0.09 ± 0.07 — —
d 7.56 ± 1.07 M⊕ 0.309 ± 0.010 106.300 ± 0.129 0.14 ± 0.04 — —

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. Koen, C.; et al. (April 21, 2010), "UBV(RI)CJHK observations of Hipparcos-selected nearby stars", Monthly Notices of the Royal Astronomical Society, 403 (4): 1949–1968, Bibcode:2010MNRAS.403.1949K, doi:10.1111/j.1365-2966.2009.16182.x.
  3. Schweitzer, A.; et al. (May 2019), "The CARMENES search for exoplanets around M dwarfs. Different roads to radii and masses of the target stars", Astronomy & Astrophysics, 625: 16, arXiv:1904.03231, Bibcode:2019A&A...625A..68S, doi:10.1051/0004-6361/201834965, A68.
  4. Stephenson, C. B. (July 1986), "Dwarf K and M stars of high proper motion found in a hemispheric survey", The Astronomical Journal, 92: 139–165, Bibcode:1986AJ.....92..139S, doi:10.1086/114146.
  5. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  6. Passegger, V. M.; et al. (October 2020), "The CARMENES search for exoplanets around M dwarfs. A deep learning approach to determine fundamental parameters of target stars", Astronomy & Astrophysics, 642: 16, arXiv:2008.01186, Bibcode:2020A&A...642A..22P, doi:10.1051/0004-6361/202038787, A22.
  7. Astudillo-Defru, N.; et al. (April 2017), "Magnetic activity in the HARPS M dwarf sample. The rotation-activity relationship for very low-mass stars through R'HK", Astronomy & Astrophysics, 600: 15, arXiv:1610.09007, Bibcode:2017A&A...600A..13A, doi:10.1051/0004-6361/201527078, S2CID 119237202, A13
  8. Miles, Brittany E.; Shkolnik, Evgenya L. (2017), "HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive", The Astronomical Journal, American Astronomical Society, 154 (2): 67, arXiv:1705.03583, Bibcode:2017AJ....154...67M, doi:10.3847/1538-3881/aa71ab, ISSN 1538-3881, S2CID 119385780.
  9. "L 736-30". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-01-15.
  10. Luyten, Willem J. (1979), LHS catalogue. A catalogue of stars with proper motions exceeding 0″.5 annually (2nd ed.), Minneapolis: University of Minnesota, Bibcode:1979lccs.book.....L.
  11. Reiners, Ansgar; et al. (April 2012), "A Catalog of Rotation and Activity in Early-M Stars", The Astronomical Journal, 143 (4): 15, arXiv:1201.5774, Bibcode:2012AJ....143...93R, doi:10.1088/0004-6256/143/4/93, 93.
  12. 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): 1545–1569, arXiv:1403.0430, Bibcode:2014MNRAS.441.1545T, doi:10.1093/mnras/stu358, S2CID 32965505.
  13. Sutherland, Paul (March 5, 2014). "Habitable planets common around red dwarf stars". Sen. Sen Corporation Ltd.
  14. "Planet Gj 180 b". Extrasolar Planets Encyclopaedia. Retrieved 2014-05-25.
  15. "Planet Gj 180 c". Extrasolar Planets Encyclopaedia. Retrieved 2014-05-25.
  16. Feng, Fabo; et al. (2020), "Search for Nearby Earth Analogs. II. Detection of Five New Planets, Eight Planet Candidates, and Confirmation of Three Planets around Nine Nearby M Dwarfs", The Astrophysical Journal Supplement Series, 246 (1): 11, arXiv:2001.02577, Bibcode:2020ApJS..246...11F, doi:10.3847/1538-4365/ab5e7c, S2CID 210064560.
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