GJ 1245

GJ 1245 (Gliese 1245) is a double star with components G 208-44 and G 208-45, located 15.2 light-years (4.7 parsecs) away in the constellation Cygnus. G 208-44 is itself a closer double star made up of two red dwarfs, while G 208-45 is also a red dwarf. GJ 1245 is the 43rd closest stellar system to the Solar System.^[14] GJ 1245 A and B are both active flare stars,^[15] and the pair are collectively designated V1581 Cygni.^[16]

V1581 Cygni

GJ 1245 Location of GJ 1245 in the constellation Cygnus
Observation data Epoch J2000      Equinox J2000
Constellation	Cygnus[1]
GJ 1245 AC
Right ascension	19h 53m 55.142s[2]
Declination	+44° 24′ 44.39″[2]
Apparent magnitude (V)	13.46 / 16.75[3]
GJ 1245 B
Right ascension	19h 53m 55.141s[4]
Declination	+44° 24′ 54.15″[4]
Apparent magnitude (V)	14.01[3]
Characteristics
Spectral type	M6V / M8V[5] / M6V[6]
Variable type	UV Cet[7]
Astrometry
Radial velocity (Rv)	3.93±0.38[4] km/s
Proper motion (μ)	RA: 349.363(56) mas/yr[4] Dec.: −480.322(54) mas/yr[4]
Parallax (π)	214.5745±0.0476 mas[4]
Distance	15.200 ± 0.003 ly (4.660 ± 0.001 pc)
Absolute magnitude (MV)	15.12 / 18.41[5] / 15.72[3]
Orbit[8]
Primary	GJ 1245 A
Companion	GJ 1245 C
Period (P)	6,147±17 days
Semi-major axis (a)	0.8267±0.0008″
Eccentricity (e)	0.334±0.002
Inclination (i)	135.7±0.1°
Longitude of the node (Ω)	261.2±0.2°
Periastron epoch (T)	51506.8±2.1
Argument of periastron (ω) (secondary)	36.1±0.2°
Details
GJ 1245 A
Mass	0.120±0.001[5] M☉
Radius	0.146±0.007[5] R☉
Luminosity	0.0014[5] L☉
Temperature	2,927[5] K
Metallicity [Fe/H]	−0.07[5] dex
Age	~300[citation needed] Myr
GJ 1245 C
Mass	0.081±0.001[5] M☉
Radius	0.087±0.004[5] R☉
Luminosity	0.0003[5] L☉
Temperature	2,611[5] K
Metallicity [Fe/H]	−0.08[5] dex
GJ 1245 B
Mass	0.115[9] M☉
Radius	0.142[9] R☉
Luminosity	0.00123[9] L☉
Surface gravity (log g)	5.20[9] cgs
Temperature	2.865[9] K
Metallicity [Fe/H]	−0.05[10] dex
Rotation	0.71[11] days
Rotational velocity (v sin i)	7[11] km/s
Age	3.1[10] Gyr
Other designations
V1581 Cyg, GJ 1245, WDS J19539+4425
GJ 1245 AC: G 208-44, LHS 3494, NLTT 48414, KIC 8451868, 2MASS J19535443+4424541[12]
GJ 1245 B: G 208-45, LHS 3495, NLTT 48415, KIC 8451881, 2MASS J19535508+4424550[6]
Database references
	AC
	B

Blue band light curve for a flare of V1581 Cygni. The left-most point shows a 1 sigma error bar. Adapted from Cristaldi and Rodonò (1976)^[13]

The largest of the three stars, GJ 1245 A (G 208-44 A) is only 12% the Sun's mass.^[5] Of the other two stars, GJ 1245 C (G 208-44 B), is closest to star A at 2 AU away;^[17] it is 8% of the Sun's mass.^[5] The third star, GJ 1245 B (G 208-45), is 27 AU away from star A,^[17] and is estimated to complete an orbit every 279 years.^[18] It is slightly smaller and less luminous than GJ 1245 A.^[9]

See also

• List of nearest stars