Gliese 105

Gliese 105 (also known as 268 G. Ceti) is a triple star system in the constellation of Cetus. It is located relatively near the Sun at a distance of 23.6 light-years (7.2 parsecs).[10][12] Despite this, even the brightest component is barely visible with the unaided eye (see Bortle scale). No planets have yet been detected around any of the stars in this system.

Gliese 105

Gliese 105 A (left) and C (right).
Observation data Epoch J2000      Equinox J2000
Constellation	Cetus
Gliese 105 A
Right ascension	02h 36m 04.89466s[1]
Declination	+06° 53′ 12.7466″[1]
Apparent magnitude (V)	5.83[2]
Gliese 105 B
Right ascension	02h 36m 15.357s[3]
Declination	+06° 52′ 19.14″[3]
Apparent magnitude (V)	11.670[4]
Gliese 105 C
Right ascension	02h 36m 04.66s[5]
Declination	+06° 53′ 14.8″[5]
Apparent magnitude (V)	16.77[5]
Characteristics
Gliese 105 AC
Spectral type	K3 V[2] + M7 V[6]
U−B color index	+0.800[7]
B−V color index	+0.972[7]
Gliese 105 B
Spectral type	M4.0 V
U−B color index	+1.10[8]
B−V color index	+1.61[8]
Variable type	BY Dra
Astrometry
Gliese 105 A
Radial velocity (Rv)	25.8 ± 0.1[9] km/s
Proper motion (μ)	RA: 1778.585±0.430[10] mas/yr Dec.: 1477.306±0.248[10] mas/yr
Parallax (π)	138.3400 ± 0.3177 mas[10]
Distance	23.58 ± 0.05 ly (7.23 ± 0.02 pc)
Absolute magnitude (MV)	6.50[11]
Gliese 105 B
Proper motion (μ)	RA: 1801.671±0.043[12] mas/yr Dec.: 1450.487±0.038[12] mas/yr
Parallax (π)	138.4371 ± 0.0420 mas[12]
Distance	23.560 ± 0.007 ly (7.223 ± 0.002 pc)
Orbit[13]
Period (P)	76.107 ± 1.820 yr
Semi-major axis (a)	17.0 ± 0.7 au
Eccentricity (e)	0.641 ± 0.004
Inclination (i)	45.5 ± 2.8°
Longitude of the node (Ω)	122.5 ± 3.4°
Periastron epoch (T)	JD 2430414 ± 669
Argument of periastron (ω) (primary)	133.4 ± 0.6°
Semi-amplitude (K1) (primary)	711.7 ± 2.2 km/s
Details
Gliese 105 A
Mass	0.70 ± 0.10[14] M☉
Radius	0.650 ± 0.053[2] R☉
Luminosity (bolometric)	0.26[14] L☉
Surface gravity (log g)	4.40 ± 0.24[15] cgs
Temperature	4777 ± 91[15] K
Metallicity [Fe/H]	−0.03 ± 0.09[15] dex
Gliese 105 B
Mass	0.246 ± 0.025[4] M☉
Radius	0.278 ± 0.010[4] R☉
Temperature	3284 ± 60[4] K
Metallicity [Fe/H]	−0.12 ± 0.03[4] dex
Other designations
268 G. Cet, Gl 105, CCDM J02361+0653, BD+06° 398
Gliese 105 AC: HR 753, HD 16160, LHS 15, LTT 10858, SAO 110636, FK5 1073, G 73-70, G 76-11, LFT 217, HIP 12114
Gliese 105 B: BX Cet, LHS 16, LTT 10859, G 73-71, G 76-12, LFT 217
Database references
SIMBAD	Gl 105
	Gl 105 A
	Gl 105 B
	Gl 105 C
Gliese 105 Location of Gliese 105 in the constellation Cetus

This is a triple system with three stars that are all less massive than the Sun. The brightest component is designated HD 16160, and is known as Gliese 105 A. It is a K-type main-sequence star,[2] about 70% the mass of the Sun.[14] This star is unusual because its eruptions appear to not conform to the Waldmeier effect—i.e., the strongest eruptions of HD 16160 are not the ones characterized by the fast eruption onset.[16]

A nearby star has a similar proper motion to Gliese 105 A, so it is assumed to be physically associated with the primary, and is known as Gliese 105 B. The two have an estimated separation of 1,200 astronomical units (au). It is a BY Draconis variable star whose brightness varies between 11.64 and 11.68 magnitudes; for that reason it has been given the designation BX Ceti.[17]

A third companion, known as Gliese 105 C, lies much closer to A, currently at a distance of approximately 24 au.[6] The pair A-C have an estimated orbital period of about 70 years.[13] While detected directly, Gliese 105 C has also been observed to perturb Gliese 105 A from its usual position;[6] from that, its orbit is estimated to have a high eccentricity of around 0.64 and a semimajor axis of 17 au.[13] Gliese 105 C is an extremely faint red dwarf.[6] It is roughly 8 to 9 percent the mass of the Sun, and it is about 20,000 times fainter than its parent star in visible light—at a distance of 1 au (the distance from the Earth to the Sun) it would only be four times brighter than the full moon.[18]