Krüger 60 (DO Cephei) is a binary star system located 13.1 light-years (4.0 parsecs) from the Sun. These red dwarf stars orbit each other every 44.6 years.

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Quick Facts Observation data Epoch J2000 Equinox, Apparent magnitude (V) ...

Krüger 60 A/B

A blue band light curve for a flare on DO Cephei, adapted from Dal (2020)[1]
Observation data Epoch J2000      Equinox
Constellation	Cepheus
Krüger 60 A
Right ascension	22h 27m 59.55755s[2]
Declination	+57° 41′ 42.0806″[2]
Apparent magnitude (V)	9.59[citation needed]
Krüger 60 B
Right ascension	22h 27m 59.79560s[3]
Declination	+57° 41′ 49.7468″[3]
Apparent magnitude (V)	11.40[citation needed]
Characteristics
Spectral type	M3V/M4V[4]
U−B color index	1.27/1.3[citation needed]
B−V color index	1.65/1.8[citation needed]
Variable type	None/Flare star
Astrometry
Krüger 60 A
Radial velocity (Rv)	–33.1[citation needed] km/s
Proper motion (μ)	RA: −725.227±0.537[2] mas/yr Dec.: −223.461±0.348[2] mas/yr
Parallax (π)	249.3926 ± 0.1653 mas[2]
Distance	13.078 ± 0.009 ly (4.010 ± 0.003 pc)
Absolute magnitude (MV)	11.76
Krüger 60 B
Radial velocity (Rv)	–31.9[citation needed] km/s
Proper motion (μ)	RA: −934.098±1.319[3] mas/yr Dec.: −686.244±1.410[3] mas/yr
Parallax (π)	249.9668 ± 0.7414 mas[3]
Distance	13.05 ± 0.04 ly (4.00 ± 0.01 pc)
Absolute magnitude (MV)	13.46
Details
Krüger 60 A
Mass	0.271[5] M☉
Radius	0.35[6] R☉
Luminosity	0.010[citation needed] L☉
Temperature	3,180[citation needed] K
Metallicity	–0.04[7]
Krüger 60 B
Mass	0.176[5] M☉
Radius	0.24[6] R☉
Luminosity	0.0034[citation needed] L☉
Temperature	2,890[citation needed] K
Orbit[8]
Primary	Krüger 60 A
Companion	Krüger 60 B
Period (P)	44.67 yr
Semi-major axis (a)	2.383″
Eccentricity (e)	0.410
Inclination (i)	167.2°
Longitude of the node (Ω)	154.5°
Periastron epoch (T)	1970.22
Argument of periastron (ω) (primary)	211.0°
Other designations
BD+56° 2783, GJ 860 A/B, HD 239960, HIP 110893, ADS 15972, G 232-075, LHS 3814/3815[9]
Database references
SIMBAD	The system
	A
	B
Krüger 60 Location of Krüger 60 in the constellation Cepheus

Close

The larger, primary star is designated component A, while the secondary, smaller star is labeled component B. Component A has about 27% of the Sun's mass and 35% of the Sun's radius. Component B has about 18% of the Sun's mass and 24% of the Sun's radius.^[5][6] Component B is a flare star and has been given the variable star designation "DO Cephei".^[10] It is an irregular flare that typically doubles in brightness and then returns to normal over an 8-minute period.^{[citation needed]}

On average, the two stars are separated by 9.5 AUs, which is roughly the average distance of Saturn from the Sun. However, their eccentric mutual orbit causes their distance to vary between 5.5 AUs at periastron, to 13.5 at apastron.^{[citation needed]}

This system is orbiting through the Milky Way at a distance from the core that varies from 7–9 kpc with an orbital eccentricity of 0.126–0.130.^[11] The closest approach to the Sun will occur in about 88,600 years when this system will come within 1.95 parsecs.^[12]

Considering the orbit of the members of Krüger 60, detecting an exoplanet through radial velocity could prove difficult, as its orbit would be inclined only 13 degrees from our point of view, and create 1/5th as strong a radial velocity signal as an exoplanet orbiting edge-on from the point of view of the Solar System.

Krüger 60 was proposed as the origin of interstellar comet 2I/Borisov (formerly named C/2019 Q4 (Borisov)) in a preprint submitted to arXiv by Dybczyński, Królikowska, and Wysoczańska.^[13] These authors had from other work a list of stars and stellar systems that can potentially act as perturbers of the Oort cloud comets, and searched it for a past close proximity of 2I/Borisov at a very small relative velocity. While hampered by uncertainty about the orbit of 2I/Borisov and particularly its non-gravitational acceleration (due to cometary outgassing), they initially reached a conclusion that 1 Myr ago 2I/Borisov passed Krüger 60 at a small distance of 1.74 pc while having an extremely small relative velocity of 3.43 km/s. Perturbations of 2I/Borisov's incoming orbit altered the intersection distance with relatively small changes in the relative velocity. However, further study by the same authors presented in the revised version of the preprint instead ruled out the possibility of Krüger 60 as a home system for 2I/Borisov.^[13]

• List of nearest stars and brown dwarfs