BO Microscopii

BO Microscopii (BO Mic) is a star in the constellation Microscopium located about 170 light-years (52 parsecs; 11 million astronomical units) from the Sun. It has been dubbed "Speedy Mic" because of its very rapid rotation. The projected rotational velocity at the equator of this star is about 135 km/s (84 mi/s), which, with an estimated inclination of 70° to the line of sight from the Earth, means it completes a rotation every 0.380 ± 0.004 days (9.120 ± 0.096 hours).

BO Microscopii

A visual band light curve for BO Microscopii, adapted from Cutispoto et al. (1997)[1]
Observation data Epoch J2000      Equinox J2000
Constellation	Microscopium
Right ascension	20h 47m 45.00562s[2]
Declination	−36° 35′ 40.7698″[2]
Apparent magnitude (V)	9.39[3]
Characteristics
Spectral type	K3Ve[3]
Variable type	Flare star
Astrometry
Radial velocity (Rv)	−5.64±2.03[2] km/s
Proper motion (μ)	RA: 18.735 mas/yr[2] Dec.: −81.712 mas/yr[2]
Parallax (π)	19.5983±0.5745 mas[2]
Distance	166 ± 5 ly (51 ± 1 pc)
Absolute magnitude (MV)	5.92[4]
Details
Mass	0.82±0.08[5] M☉
Radius	1.06±0.04[5] R☉
Temperature	4750±50[6] K
Metallicity [Fe/H]	−1.49[4] dex
Rotation	0.380±0.004 days[1]
Rotational velocity (v sin i)	135[7] km/s
Age	33±5[6] Myr
Other designations
Speedy Mic, BO Mic, CD−37 13926, CPD−37 8883, HD 197890, HIP 102626, SAO 212437, PPM 300614, TIC 389423271, TYC 7469-997-1, GSC 07469-00997
Database references
SIMBAD	data

The photosphere of this star shows a high level of magnetic activity, with multiple star spots and prominences observed at the same time. As many as 25 prominences have been observed simultaneously, extending outward as far as 3.6 times the radius of the star. BO Mic is a flare star that undergoes sudden increases in X-ray and ultraviolet emissions. These events can emit a hundred times more energy than large solar flares.^[7] Speedy Mic is one of the most active stars in the vicinity of the Sun.^[5]