Mu Columbae

Mu Columbae (μ Col, μ Columbae) is a star in the constellation of Columba. It is one of the few O-class stars that are visible to the unaided eye.^[8] The star is known to lie approximately 1,900 light years from the Solar System (with an error margin of a few hundred light years).^[6]

μ Columbae

Location of μ Columbae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Columba
Right ascension	05h 45m 59.89502s[1]
Declination	−32° 18′ 23.1623″[1]
Apparent magnitude (V)	5.18[2]
Characteristics
Spectral type	O9.5 V[3]
U−B color index	−1.06[2]
B−V color index	−0.28[2]
Variable type	Suspected[4]
Astrometry
Radial velocity (Rv)	+109.00 ± 1.8[5] km/s
Proper motion (μ)	RA: +3.271 mas/yr[1] Dec.: −22.176 mas/yr[1]
Parallax (π)	1.7024±0.0898 mas[1]
Distance	1,890±110 ly (581±34 pc)[6]
Absolute magnitude (MV)	−3.78±0.11[6]
Details[6]
Mass	18.9±0.3 M☉
Radius	6.3±0.4 R☉
Luminosity	43,650+4,210 −3,840 L☉
Surface gravity (log g)	4.12±0.05 cgs
Temperature	33,400±300 K
Rotational velocity (v sin i)	125±8 km/s
Age	2 – 4[7] Myr
Other designations
HR 1996, CD−32°2538, HD 38666, SAO 196149, HIP 27204
Database references
SIMBAD	data

This is a relatively fast rotating star that completes a full revolution approximately every 1.5 days. (Compare this to the Sun, which at only 22 percent of this star's diameter rotates only once every 25.4 days.) This rate of rotation is fairly typical for stars of this class.

Based on measurements of proper motion and radial velocity, astronomers know that this star and AE Aurigae are moving away from each other at a relative velocity of over 200 km/s. Their common point of origin intersects with Iota Orionis in the Trapezium cluster, some two and half million years in the past. The most likely scenario that could have created these runaway stars is a collision between two binary star systems, with the stars being ejected along different trajectories radial to the point of intersection.^[9]

Etymology

In Chinese astronomy, Mu Columbae is called 屎, Pinyin: Shǐ, meaning "Excrement" or "The Secretions", because this star is marking itself and stand alone in the asterism of the same name within the Three Stars mansion.^[10][11]