Lacaille 8760

Lacaille 8760 (AX Microscopii) is a red dwarf star in the constellation Microscopium. It is one of the nearest stars to the Sun at about 12.9 light-years' distance, and the brightest M dwarf star in Earth's night sky, although it is generally too faint to be seen without a telescope. At an apparent magnitude of +6.7, it may only be visible to the unaided eye under exceptionally good viewing conditions, under dark skies. It was originally listed in a 1763 catalog that was published posthumously by the French Abbé Nicolas Louis de Lacaille. He observed it in the southern sky while working from an observatory at the Cape of Good Hope.[11]

Lacaille 8760
Observation data
Epoch J2000      Equinox J2000
Constellation Microscopium
Right ascension 21h 17m 15.2697s[1]
Declination −38° 52′ 02.502″[1]
Apparent magnitude (V) 6.67[2]
Characteristics
Spectral type M0Ve[3][4]
U−B color index +1.165[3]
B−V color index +1.395[3]
Variable type Flare star
Astrometry
Radial velocity (Rv)+20.7[4] km/s
Proper motion (μ) RA: -3258.79[1] mas/yr
Dec.: -1146.51[1] mas/yr
Parallax (π)253.41 ± 0.80[5] mas
Distance12.87 ± 0.04 ly
(3.95 ± 0.01 pc)
Absolute magnitude (MV)8.69[2]
Details
Mass0.60[2] M☉
Radius0.51[6] R☉
Luminosity (bolometric)0.072[7] L☉
Luminosity (visual, LV)0.029 L☉
Surface gravity (log g)4.78[6] cgs
Temperature3,800[8] K
Metallicity [Fe/H]−0.01±0.04[9] dex
Rotation40 ± 12 days[10]
Rotational velocity (v sin i)3.3[4] km/s
Age< 0.40[6] Gyr
Other designations
AX Microscopii, AX Mic, GJ 825, HD 202560, LHS 66, CD-39°14192, GCTP 5117, HIP 105090.[3]
Database references
SIMBADdata
Exoplanet Archivedata
ARICNSdata

In the past Lacaille 8760 has been classified anywhere from spectral class K7 down to M2. In 1979 the Irish astronomer Patrick Byrne discovered that it is a flare star,[12] and it was given the variable star designation AX Microscopii. As a flare star it is relatively quiet, only erupting on average less than once per day.

Lacaille 8760 orbits around the galaxy with a relatively high ellipticity of 0.23.[13] Its closest approach to the Sun occurred about 20,000 years ago when it came within 12 light-years (3.7 parsecs).[14] Due to its low mass (60% of the Sun), it has an expected lifespan of about 75 billion (7.5 × 1010) years,[15] seven times longer than the Sun's.

Despite efforts by astronomers, as of 2011 no planets had been detected in orbit around this star.[16]

Lacaille 8760 is one of the largest and brightest red dwarfs known, with about 60% the mass and 51% the radius of the Sun.

References
  1. Perryman, M. A. C.; et al. (July 1997), "The HIPPARCOS Catalogue", Astronomy and Astrophysics, 323: L49–L52, Bibcode:1997A&A...323L..49P.
  2. "The One Hundred Nearest Star Systems", RECONS, Georgia State University, retrieved 2015-06-25.
  3. "V* AX Mic -- Flare Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2011-02-18.
  4. Torres, C. A. O.; et al. (December 2006), "Search for associations containing young stars (SACY). I. Sample and searching method", Astronomy and Astrophysics, 460 (3): 695–708, arXiv:astro-ph/0609258, Bibcode:2006A&A...460..695T, doi:10.1051/0004-6361:20065602, S2CID 16080025. See the online data.
  5. van Leeuwen, F. (2007). "HIP 105090". Validation of the new Hipparcos reduction. Retrieved 2017-06-12.
  6. Takeda, Genya; et al. (February 2007), "Structure and Evolution of Nearby Stars with Planets. II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog", The Astrophysical Journal Supplement Series, 168 (2): 297–318, arXiv:astro-ph/0607235, Bibcode:2007ApJS..168..297T, doi:10.1086/509763, S2CID 18775378, retrieved 2011-08-26.
  7. Moro-Martín, A.; et al. (March 2015). "Does the Presence of Planets Affect the Frequency and Properties of Extrasolar Kuiper Belts? Results from the Herschel Debris and Dunes Surveys". The Astrophysical Journal. 801 (2): 28. arXiv:1501.03813. Bibcode:2015ApJ...801..143M. doi:10.1088/0004-637X/801/2/143. S2CID 55170390.Vizier catalog entry
  8. Gautier, Thomas N., III; et al. (September 2007), "Far-Infrared Properties of M Dwarfs", The Astrophysical Journal, 667 (1): 527–536, arXiv:0707.0464, Bibcode:2007ApJ...667..527G, doi:10.1086/520667, S2CID 15732144.
  9. Lindgren, Sara; Heiter, Ulrike (2017). "Metallicity determination of M dwarfs. Expanded parameter range in metallicity and effective temperature". Astronomy and Astrophysics. 604: A97. arXiv:1705.08785. Bibcode:2017A&A...604A..97L. doi:10.1051/0004-6361/201730715. S2CID 119216828.
  10. Byrne, P. B.; Doyle, J. G. (January 1989), "Activity in late-type dwarfs. III - Chromospheric and transition region line fluxes for two dM stars", Astronomy and Astrophysics, 208 (1–2): 159–165, Bibcode:1989A&A...208..159B.
  11. Croswell, Ken (July 2003), "The Brightest Red Dwarf", Sky & Telescope: 32, retrieved 2011-02-18.
  12. Byrne, P. B. (April 1981), "Gliese 825 - A new flare star", Monthly Notices of the Royal Astronomical Society, 195 (2): 143–147, Bibcode:1981MNRAS.195..143B, doi:10.1093/mnras/195.2.143.
  13. Allen, C.; Herrera, M. A. (April 1998), "The Galactic Orbits of Nearby UV Ceti Stars", Revista Mexicana de Astronomía y Astrofísica, 34: 37–46, Bibcode:1998RMxAA..34...37A.
  14. García-Sánchez, J.; et al. (2001), "Stellar encounters with the solar system" (PDF), Astronomy and Astrophysics, 379 (2): 634–659, Bibcode:2001A&A...379..634G, doi:10.1051/0004-6361:20011330.
  15. Despain, K. H. (December 1981), "Low-mass evolution - Zero-age main sequence to asymptotic giant branch", Astrophysical Journal, Part 1, 251: 639–653, Bibcode:1981ApJ...251..639D, doi:10.1086/159510.
  16. Carson, J. C.; et al. (December 2011), "Low-mass evolution - Zero-age main sequence to asymptotic giant branch", The Astrophysical Journal, 743 (2): 141, arXiv:1110.2191, Bibcode:2011ApJ...743..141C, doi:10.1088/0004-637X/743/2/141, S2CID 119270911.

Notes
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