20 Ophiuchi

20 Ophiuchi is a class F6IV^[3] (yellow-white subgiant) star in the constellation Ophiuchus. Its apparent magnitude is 4.64^[2] and it is approximately 104 light years away based on parallax.^[1] It lies near the star Zeta Ophiuchi.

20 Ophiuchi

Location of 20 Ophiuchi (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Ophiuchus
Right ascension	16h 49m 50.01604s[1]
Declination	−10° 46′ 58.7775″[1]
Apparent magnitude (V)	4.64[2]
Characteristics
Spectral type	F6IV[3]
U−B color index	+0.07[4]
B−V color index	+0.47[4]
Astrometry
Radial velocity (Rv)	−1.60[5] km/s
Proper motion (μ)	RA: +72.33[1] mas/yr Dec.: −78.80[1] mas/yr
Parallax (π)	31.27±2.16 mas[1]
Distance	104 ± 7 ly (32 ± 2 pc)
Absolute magnitude (MV)	2.13[2]
Orbit[6]
Period (P)	35.5 ± 1.5 yr
Semi-major axis (a)	0.460 ± 0.030″
Eccentricity (e)	0.8 ± 0.2
Inclination (i)	74 ± 11°
Longitude of the node (Ω)	118 ± 9°
Periastron epoch (T)	1981.2 ± 1.7
Argument of periastron (ω) (secondary)	34 ± 26°
Details
20 Oph A
Mass	1.70[7] M☉
Radius	3.0[7] R☉
Luminosity	12.06[2] L☉
Surface gravity (log g)	3.89[8] cgs
Temperature	6,417[8] K
Metallicity [Fe/H]	+0.13[8] dex
Rotational velocity (v sin i)	11.3[9] km/s
20 Oph B
Mass	0.8 ± 0.2[6] M☉
Other designations
BD−10°4394, FK5 1438, GC 22643, HIP 82369, HR 6243, HD 151769, SAO 160118
Database references
SIMBAD	data

20 Ophiuchi is an astrometric binary. The primary star is a late F-type subgiant star. It has a mass 1.72 times that of the Sun.^[6] The companion star regularly perturbs the primary star, causing it to wobble around the barycenter. From this, an orbital period of 35.5 years has been calculated. The secondary star is 0.8 times the mass of the Sun, and it may be a white dwarf or red dwarf.^[6]