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)14.9842 ± 0.2701[3] mas
Distance218 ± 4 ly
(67 ± 1 pc)
Absolute magnitude (MV)5.92[4]
Mass0.82 ± 0.08[5] M
Radius1.06 ± 0.04[5] R
Diameter1.06 ± 0.04[5] D
Metallicity [Fe/H]−1.49[4] dex
Rotational velocity (v sin i)135[6] km/s
Other designations
CD−37 13926, HD 197890, SAO 212437, HIP 102626.
Database references

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). 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.[6] Speedy Mic is one of the most active stars in the vicinity of the Sun.[5]


  1. 1.0 1.1 1.2 1.3 van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. arXiv:0708.1752. Bibcode 2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. 2.0 2.1 2.2 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
  3. Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. arXiv:1804.09365. Bibcode 2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  4. 4.0 4.1 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:0811.3982, Bibcode 2009A&A...501..941H, doi:10.1051/0004-6361/200811191
  5. 5.0 5.1 5.2 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/0510739, Bibcode 2006MNRAS.365..530D, doi:10.1111/j.1365-2966.2005.09729.x
  6. 6.0 6.1 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:0712.0899, Bibcode 2008A&A...478L..11W, doi:10.1051/0004-6361:20078838

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