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-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.

Lacaille 8760

Image of Lacaille 8760 (circled) in Bode's Uranographia (1801).[1] In the corresponding catalog this star is listed as № 36 in constellation Microscopium.[2]
Observation data Epoch J2000      Equinox J2000
Constellation	Microscopium
Right ascension	21h 17m 15.26907s[3]
Declination	−38° 52′ 02.5039″[3]
Apparent magnitude (V)	6.67[4]
Characteristics
Spectral type	M0Ve[5][6]
U−B color index	+1.165[5]
B−V color index	+1.395[5]
Variable type	Flare star
Astrometry
Radial velocity (Rv)	+20.71±0.12[3] km/s
Proper motion (μ)	RA: −3,258.966 mas/yr[3] Dec.: −1,145.862 mas/yr[3]
Parallax (π)	251.9124 ± 0.0352 mas[3]
Distance	12.947 ± 0.002 ly (3.9696 ± 0.0006 pc)
Absolute magnitude (MV)	8.69[4]
Details
Mass	0.60[4] M☉
Radius	0.51[7] R☉
Luminosity (bolometric)	0.072[8] L☉
Luminosity (visual, LV)	0.029 L☉
Surface gravity (log g)	4.78[7] cgs
Temperature	3,800[9] K
Metallicity [Fe/H]	−0.01±0.04[10] dex
Rotation	40±12 d[11]
Rotational velocity (v sin i)	3.3[6] km/s
Age	4.8±2.9[12] Gyr
Other designations
AX Microscopii, AX Mic, CD−39°14192, GJ 825, HD 202560, HIP 105090, LHS 66[5]
Database references
SIMBAD	data
Exoplanet Archive	data
ARICNS	data
Lacaille 8760 Location of Lacaille 8760 in the constellation Microscopium

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.^[13] Number 8760 was assigned to this star in the 1847 edition of Lacaille's catalogue of 9,766 stars by Francis Baily.^[14]

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,^[15] 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)^[15]

Lacaille 8760 is one of the largest and brightest red dwarfs known, with about 60%^[4] the mass and 51%^[7] the radius of the Sun. It is about five^[12] 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.^[11] The star is radiating 7.2%^[8] of the luminosity of the Sun from its photosphere at an effective temperature of 3,800 K.^[9]

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

Lacaille 8760 orbits around the galaxy with a relatively high ellipticity of 0.23.^[17] Its closest approach to the Sun occurred about 20,000 years ago when it came within 12 light-years (3.7 parsecs).^[18] Due to its low mass (60% of the Sun), it has an expected lifespan of about 75 billion (7.5 × 10¹⁰) years,^[19] 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. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
4. "The One Hundred Nearest Star Systems", RECONS, Georgia State University, retrieved 2015-06-25.
5. "V* AX Mic -- Flare Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2011-02-18.
6. 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. 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.
8. 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
9. 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)
10. 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.
11. 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.
12. 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.
13. Croswell, Ken (July 2003), "The Brightest Red Dwarf", Sky & Telescope: 32, retrieved 2011-02-18.
14. Francis Baily. A Catalogue of 9766 Stars (1847), Page 219
15. 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.
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.
17. 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.
18. 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.
19. 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.

External links

• SolStation article