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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-class main-sequence 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.

This star 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.[14] Number 8760 was assigned to this star in the 1847 edition of Lacaille's catalogue of 9,766 stars by Francis Baily.[15]

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,[16] and it was given the variable star designation AX Microscopii, or AX Mic. As a flare star it is relatively quiescent.

An ultraviolet band light curve for a flare on AX Microscopii, adapted from Byrne (1981)[16]

Lacaille 8760 is one of the largest and brightest red dwarfs known, with about 60%[4] the mass and 51%[8] the radius of the Sun. It is about five[13] billion years old and is spinning at a projected rotational velocity of 3.3 km/s,[6] giving it a rotation period of roughly 40 days.[12] The star is radiating 7.2%[9] of the luminosity of the Sun from its photosphere at an effective temperature of 3,800 K.[10]

Despite efforts by astronomers, as of 2011 no planets had been detected in orbit around this star.[17]

Lacaille 8760 orbits around the galaxy with a relatively high ellipticity of 0.23.[18] Its closest approach to the Sun occurred about 20,000 years ago when it came within 12 light-years (3.7 parsecs).[19] Due to its low mass (60% of the Sun), it has an expected lifespan of about 75 billion (7.5 × 1010) years,[20] seven times longer than the Sun's.

References

  1. ^ e-rara.ch. Johann Elert Bode. Uranographia star atlas (1801), Tabula XVI
  2. ^ Johann Elert Bode. Allgemeine Beschreibung und Nachweisung der Gestirne (1801), Page 67
  3. ^ a b c 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.
  4. ^ a b c d "The One Hundred Nearest Star Systems", RECONS, Georgia State University, retrieved 2015-06-25.
  5. ^ a b c d "V* AX Mic -- Flare Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2011-02-18.
  6. ^ a b c d 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.
  7. ^ Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  8. ^ a b c 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.
  9. ^ a b 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
  10. ^ a b 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.{{citation}}: CS1 maint: multiple names: authors list (link)
  11. ^ 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.
  12. ^ a b 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.
  13. ^ a b Boehle, A.; et al. (October 2019), "Combining high-contrast imaging and radial velocities to constrain the planetary architectures of nearby stars", Astronomy & Astrophysics, 630: 17, arXiv:1907.04334, Bibcode:2019A&A...630A..50B, doi:10.1051/0004-6361/201935733, S2CID 195874049, A50.
  14. ^ Croswell, Ken (July 2003), "The Brightest Red Dwarf", Sky & Telescope: 32, retrieved 2011-02-18.
  15. ^ Francis Baily. A Catalogue of 9766 Stars (1847), Page 219
  16. ^ a b 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.
  17. ^ 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.
  18. ^ 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.
  19. ^ 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.
  20. ^ 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.

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