Struve 2398

Struve 2398 (Gliese 725) is a binary star system in the northern constellation of Draco. Struve 2398 is star number 2398 in the Struve Double Star Catalog of Russian-German astronomer Friedrich Georg Wilhelm von Struve. The astronomer's surname, and hence the star identifier, is sometimes indicated by a Greek sigma, Σ; hence, this system can be listed with the identifier Σ 2398. Although the components are too faint to be viewed with the naked eye, this star system is among the closest to the Sun. Parallax measurements by the Gaia spacecraft give them an estimated distance of 11.5 light-years (3.5 parsecs) away.

ConstellationDraco^[1][2]

Right ascension18^h 42^m 46.70439^s[3]

Declination+59° 37′ 49.4095″^[3]

Apparentmagnitude(V)8.94^[4]

Quick facts Constellation, Right ascension ...

Struve 2398

Struve 2398 Location of Struve 2398 in the constellation Draco
Observation data Epoch J2000      Equinox ICRS
Constellation	Draco[1][2]
Struve 2398 A
Right ascension	18h 42m 46.70439s[3]
Declination	+59° 37′ 49.4095″[3]
Apparent magnitude (V)	8.94[4]
Struve 2398 B
Right ascension	18h 42m 46.89467s[5]
Declination	+59° 37′ 36.7212″[5]
Apparent magnitude (V)	9.70[4]
Characteristics
A
Evolutionary stage	red dwarf[6]
Spectral type	M3V[7]
U−B color index	1.10[8]
B−V color index	1.54[8]
Variable type	Flare star[9]
B
Evolutionary stage	red dwarf[6]
Spectral type	M3.5V[7]
U−B color index	1.14[8]
B−V color index	1.59[8]
Astrometry
Struve 2398 A
Radial velocity (Rv)	−1.30±0.12[3] km/s
Proper motion (μ)	RA: –1311.679 mas/yr[3] Dec.: +1792.325 mas/yr[3]
Parallax (π)	283.8401±0.0220 mas[3]
Distance	11.4908 ± 0.0009 ly (3.5231 ± 0.0003 pc)
Absolute magnitude (MV)	+11.18[1]
Struve 2398 B
Radial velocity (Rv)	0.88±0.15[5] km/s
Proper motion (μ)	RA: –1400.264 mas/yr[5] Dec.: +1862.525 mas/yr[5]
Parallax (π)	283.8378±0.0287 mas[5]
Distance	11.491 ± 0.001 ly (3.5231 ± 0.0004 pc)
Absolute magnitude (MV)	+12.01[2]
Orbit[10]
Period (P)	1,166±60 years
Semi-major axis (a)	63±1 AU[11]
Eccentricity (e)	0.4396±0.0038
Inclination (i)	73.8±0.3°
Longitude of the node (Ω)	145.32±0.37°
Periastron epoch (T)	1837±4
Argument of periastron (ω) (secondary)	321.3±4.2°
Details
Struve 2398 A
Mass	0.330±0.008[11] M☉
Radius	0.351±0.003[11] R☉
Luminosity	0.01552±0.00007[11] L☉
Surface gravity (log g)	4.87±0.01[11] cgs
Temperature	3,433±68[11] K
Metallicity [Fe/H]	−0.23±0.08[7] dex
Rotation	103.1±6.1[12] days
Rotational velocity (v sin i)	< 2.5[13] km/s
Age	6.2±2.3[11] Gyr
Struve 2398 B
Mass	0.25±0.02[14] M☉
Radius	0.280±0.005[14] R☉
Luminosity	0.00916±0.00006[14] L☉
Surface gravity (log g)	4.82±0.06[14] cgs
Temperature	3,379±31[14] K
Metallicity [Fe/H]	−0.30±0.08[7] dex
Rotation	105.1±3.3[14] days
Rotational velocity (v sin i)	< 2.5[13] km/s
Age	8.7±2.1[14] Gyr
Other designations
Σ 2398, BD+59°1915, GJ 725, ADS 11632
Struve 2398 A: Vyssotsky 184, NSV 11288, HD 173739, HIP 91768, G 227-046, LHS 58
Struve 2398 B: HD 173740, HIP 91772, G 227-047, LHS 59
Database references
SIMBAD	The system
	A
	B
Exoplanet Archive	data

Close

Both stars are small red dwarfs, with each having around a third the Sun's mass and radius. They are each sources of X-ray emission.^[15] They are orbiting with a period of about 871 years, at a separation of about 63 astronomical units with an orbital eccentricity of 0.29.^[11]

The pair has a relatively high proper motion of 2.2 arc seconds per year. The system is on an orbit through the Milky Way that has an eccentricity of 0.05, carrying them as close as 8 kpc and as far as 9 kpc from the Galactic Center. The plane of their galactic orbit carries them as far as 463−489 pc away from the galactic plane.^[16]