BO Microscopii

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BO Microscopii
Observation data
Epoch J2000      Equinox J2000
Constellation Microscopium
Right ascension 20h 47m 45.00732s[1]
Declination −36° 35′ 40.7905″[1]
Apparent magnitude (V) 9.39[2]
Spectral type K3Ve[2]
Variable type Flare star
Radial velocity (Rv) -10.3[2] km/s
Proper motion (μ) RA: 11.42[1] mas/yr
Dec.: −75.87[1] mas/yr
Parallax (π) 19.16 ± 1.80[1] mas
Distance 170 ± 20 ly
(52 ± 5 pc)
Absolute magnitude (MV) 5.92[3]
Mass 0.82 ± 0.08[4] M
Radius 1.06 ± 0.04[4] R
Metallicity [Fe/H] −1.49[3] dex
Rotational velocity (v sin i) 135[5] km/s
Other designations
CD−37 13926, HD 197890, SAO 212437, HIP 102626.

BO Microscopii (BO Mic) is a star in the constellation Microscopium located about 170 light years from the Sun. It has been dubbed "Speedy Mic" because of the ultra-rapid rotation rate. The projected rotational velocity at the equator of this star is about 135 km/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 hours 7 minutes). 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.[5] Speedy Mic is one of the most active stars in the vicinity of the Sun.[4]


  1. ^ a b c d e van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  2. ^ a b c 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/0609258Freely accessible, Bibcode:2006A&A...460..695T, doi:10.1051/0004-6361:20065602 
  3. ^ a b Holmberg, J.; Nordström, B.; Andersen, J. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:0811.3982Freely accessible, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191 
  4. ^ a b c Dunstone, N. J.; et al. (January 2006), "The coronal structure of Speedy Mic - I. A densely packed prominence system beyond corotation", Monthly Notices of the Royal Astronomical Society, 365 (2): 530–538, arXiv:astro-ph/0510739Freely accessible, Bibcode:2006MNRAS.365..530D, doi:10.1111/j.1365-2966.2005.09729.x 
  5. ^ a b Wolter, U.; et al. (January 2008), "Doppler imaging an X-ray flare on the ultrafast rotator BO Mic. A contemporaneous multiwavelength study using XMM-Newton and VLT", Astronomy and Astrophysics, 478 (1): L11–L14, arXiv:0712.0899Freely accessible, Bibcode:2008A&A...478L..11W, doi:10.1051/0004-6361:20078838