BU Canis Minoris

BU Canis Minoris is a quadruple star system in the equatorial constellation of Canis Minor. It has the Henry Draper Catalogue designation of HD 65241, while BU Canis Minoris is its variable star designation. The system is a challenge to view with the naked eye, having a peak apparent visual magnitude of 6.42.^[3] It is located at a distance of approximately 700 light years from the Sun based on parallax,^[2] and is drifting further away with a radial velocity of about +34 km/s.^[3]

BU Canis Minoris

A light curve for BU Canis Minoris, plotted from TESS data[1]
Observation data Epoch J2000      Equinox J2000
Constellation	Canis Minor
Right ascension	07h 58m 05.89734s[2]
Declination	+07° 12′ 48.7030″[2]
Apparent magnitude (V)	6.42[3]
Characteristics
Spectral type	A0V[4]
B−V color index	−0.031±0.008[3]
Astrometry
Radial velocity (Rv)	+34.0±6.5[3] km/s
Proper motion (μ)	RA: −9.407[2] mas/yr Dec.: −11.835[2] mas/yr
Parallax (π)	4.0663±0.0568 mas[2]
Distance	800 ± 10 ly (246 ± 3 pc)
Absolute magnitude (MV)	−0.38[3]
Orbit[5]
Primary	A
Companion	B
Period (P)	6.54 yr
Semi-major axis (a)	16.1 R☉
Eccentricity (e)	0.71
Orbit[5]
Primary	Aa
Companion	Ab
Period (P)	2.94 days
Semi-major axis (a)	16.1 R☉
Eccentricity (e)	0.20
Inclination (i)	83.89°
Orbit[5]
Primary	Ba
Companion	Bb
Period (P)	3.26 days
Semi-major axis (a)	17.3 R☉
Eccentricity (e)	0.22
Inclination (i)	83.40°
Details[5]
BU CMi Aa
Mass	3.40±0.10 M☉
Radius	2.51±0.05 R☉
Surface gravity (log g)	4.088±0.010 cgs
Temperature	10,130±80 K
BU CMi Ab
Mass	3.11±0.10 M☉
Radius	1.80±0.05 R☉
Surface gravity (log g)	4.338±0.010 cgs
Temperature	9,740±80 K
BU CMi Ba
Mass	3.29±0.10 M☉
Radius	2.31±0.05 R☉
Surface gravity (log g)	4.148±0.010 cgs
Temperature	10,180±80 K
BU CMi Bb
Mass	3.29±0.10 M☉
Radius	2.04±0.05 R☉
Surface gravity (log g)	4.259±0.010 cgs
Temperature	9,890±80 K
Other designations
BU CMi, BD+07°1879, HD 65241, HIP 38945, HR 3103, SAO 116179[6]
Database references
SIMBAD	data

BU Canis Majoris was discovered to be a variable star when the Hipparcos data was analyzed. It was given its variable star designation in 1999.^[7]

In 2021, BU Canis Majoris was found to be composed to two eclipsing binaries, totalling four stars. Both pairs are double-lined spectroscopic binary systems that form Algol-like eclipsing binaries.^[5] The orbits of both systems are somewhat eccentric.^[5] The brightness of the system decreases from 6.44 down to 6.53 during the primary eclipse.^[8] It has a stellar classification of A0V,^[4] which matches an A-type main-sequence star that is generating energy through hydrogen fusion at its core. In reality, however, all four stars are nearly equal in properties, and have masses from 3.1 to 3.4 solar masses.^[5] The system is about 200 million years old.^[5]