Stein 2051 (Gliese 169.1, G 175-034, LHS 26/27) is a nearby binary star system, containing a red dwarf (component A) and a degenerate star (white dwarf) (component B), located in constellation Camelopardalis at about 18 ly from Earth.^[12]

Quick Facts Apparent magnitude (V), Characteristics ...

Stein 2051

Image of Stein 2051 B and a background star taken by the Hubble Space Telescope.[1] Credit: NASA, ESA, and K. Sahu (STScI)
Observation data Epoch J2000      Equinox J2000
Constellation	Camelopardalis
Stein 2051 A
Right ascension	04h 31m 11.5181s[2]
Declination	+58° 58′ 37.461″[2]
Apparent magnitude (V)	10.977[2]
Stein 2051 B
Right ascension	04h 31m 12.570s[3]
Declination	+58° 58′ 41.15″[3]
Apparent magnitude (V)	11.19[3]
Characteristics
Stein 2051 A
Spectral type	M4.0Ve[2]
U−B color index	+1.21[4]
B−V color index	+1.65[4]
Stein 2051 B
Spectral type	DC5[3]
U−B color index	-0.53[4]
B−V color index	+0.31[4]
Astrometry
Stein 2051 A
Radial velocity (Rv)	29 km/s
Proper motion (μ)	RA: 1300.365 mas/yr[5] Dec.: -2046.106 mas/yr[5]
Parallax (π)	181.2438 ± 0.0499 mas[5]
Distance	17.995 ± 0.005 ly (5.517 ± 0.002 pc)
Stein 2051 B
Radial velocity (Rv)	2.0 km/s
Proper motion (μ)	RA: 1334.780±0.021[6] mas/yr Dec.: −1947.638±0.019[6] mas/yr
Parallax (π)	181.2730 ± 0.0203 mas[6]
Distance	17.993 ± 0.002 ly (5.5165 ± 0.0006 pc)
Details[7]
Stein 2051 A
Mass	0.252±0.013[8] M☉
Radius	0.292±0.031[8] R☉
Luminosity	0.0081[8] L☉
Surface gravity (log g)	4.80+0.13 −0.10 cgs
Temperature	3277+42 −75 K
Metallicity [Fe/H]	0.26+0.06 −0.22 dex
Rotational velocity (v sin i)	5.2+1.7 −2.7 km/s
Stein 2051 B
Mass	0.675±0.051[9] M☉
Radius	0.0114±0.0004[9] R☉
Temperature	7122±181[9] K
Other designations
Stein 2051, G 175-34, HIP 21088,[10] WDS J04312+5858AB, GJ 169.1,[11] PLX 986.01[12]
Stein 2051 A: LHS 26, NLTT 13373, TYC 3744-412-1, 2MASS J04311147+585837, WISE J043113.20+585816.7[2]
Stein 2051 B: EGGR 180, LHS 27, NLTT 13375, TYC 3744-2062-1, 2MASS J04311201+5858476, WD 0426+58, WD2 0426+585, WD3 0426+588[3]
Database references
SIMBAD	The system
	A
	B
Stein 2051 Location of Stein 2051 in the constellation Camelopardalis

Close

Stein 2051 is the nearest (red dwarf + white dwarf) separate binary system (40 Eridani BC is located closer at 16.26 light-years,^[13] but it is a part of a triple star system).

Stein 2051 B is the 6th nearest white dwarf after Sirius B, Procyon B, van Maanen's star, LP 145-141 and 40 Eridani B.

The brighter of these two stars is A (a red dwarf), but the more massive is component B (a white dwarf).

In 2017, Stein 2051 B was observed passing in front of a more distant star. The bending of starlight by the gravitational field of the nearer star allowed its mass to be directly measured. The estimated mass of Stein 2051 B is 0.675±0.051 M_☉, which fits the expected range of a white dwarf with a carbon-oxygen core.^[9]