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
Rotational velocity (v sin i)	3.3[6] km/s
Age	4.8±2.9[11] 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.^[12] Number 8760 was assigned to this star in the 1847 edition of Lacaille's catalogue of 9,766 stars by Francis Baily.^[13]

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,^[14] 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)^[14]

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^[11] billion years old and is spinning at a projected rotational velocity of 3.3 km/s.^[6] 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.^[15]

Lacaille 8760 orbits around the galaxy with a relatively high ellipticity of 0.23.^[16] Its closest approach to the Sun occurred about 20,000 years ago when it came within 12 light-years (3.7 parsecs).^[17] Due to its low mass (60% of the Sun), it has an expected lifespan of about 75 billion (7.5 × 10¹⁰) years,^[18] seven times longer than the Sun's.