Speedy Mic
Star in the constellation Microscopium
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Speedy Mic is a star in the constellation Microscopium located about 170 light-years (52 parsecs; 11 million astronomical units) from the Sun. Its name refers to its very rapid rotation; it also has the variable star designation BO Microscopii (BO Mic). 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).[10]
 Map of starspots on the surface of Speedy Mic at different rotation phases. The blue circle is the location of a flare observed in October 2006. | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Microscopium[1] |
| 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 | BY Dra[4] |
| 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) | +6.22[1] |
| Details | |
| Mass | 0.82±0.08[5] M☉ |
| Radius | 1.06±0.04[5] R☉ |
| Luminosity | 0.60[6] L☉ |
| Surface gravity (log g) | 4.28[6] cgs |
| Temperature | 4750±50[7] K |
| Metallicity [Fe/H] | −1.49[8] dex |
| Rotation | 0.380±0.004 days[9] |
| Rotational velocity (v sin i) | 135[10] km/s |
| Age | 33±5[7] 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 star was discovered to be active and a rapid rotator in a 1990 all-sky extreme ultraviolet survey by the ROSAT space telescope, and was given the name Speedy Mic; Mic is the abbreviation for Microscopium.[11] The name has been commonly used since and was officially approved by the IAU Working Group on Star Names on 9 May 2026.[12]
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.[10] Speedy Mic is one of the most active stars in the vicinity of the Sun.[5]