Upsilon Ophiuchi

Upsilon Ophiuchi is a quadruple star system in the equatorial constellation of Ophiuchus. It has a white hue and is faintly visible to the naked eye with an apparent visual magnitude of 4.62. The distance to this system is approximately 130 light years based on parallax. It is drifting closer with a radial velocity of −30.6 km/s.

Upsilon Ophiuchi

Location of υ Ophiuchi (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Ophiuchus[1]
Right ascension	16h 27m 48.17331s[2]
Declination	−08° 22′ 18.4156″[2]
Apparent magnitude (V)	4.62[1]
Characteristics
Spectral type	kA2hA5VmA5[3]
U−B color index	+0.06[4]
B−V color index	+0.16[4]
Astrometry
Radial velocity (Rv)	−30.60[5] km/s
Proper motion (μ)	RA: −97.526[2] mas/yr Dec.: −33.97[2] mas/yr
Parallax (π)	25.0819±0.2300 mas[2]
Distance	130 ± 1 ly (39.9 ± 0.4 pc)
Absolute magnitude (MV)	1.75[1]
Orbit[6]
Primary	Aa1
Companion	Aa2
Period (P)	27.218±0.0005 d
Semi-major axis (a)	≥ 0.0583 AU
Eccentricity (e)	0.744±0.002
Periastron epoch (T)	2,438,914.84±0.01 JD
Argument of periastron (ω) (secondary)	333.7±0.7°
Semi-amplitude (K1) (primary)	34.9±0.3 km/s
Semi-amplitude (K2) (secondary)	41.1±0.3 km/s
Orbit[7]
Primary	Aa
Companion	Ab
Period (P)	82.8±1.4 yr
Semi-major axis (a)	0.79±0.03″
Eccentricity (e)	0.45±0.03
Inclination (i)	31.2±5.7°
Longitude of the node (Ω)	86.8±6.9°
Periastron epoch (T)	B 1994.1±1.0
Argument of periastron (ω) (secondary)	177.9±7.4°
Details
Aa1
Mass	1.83[8] M☉
Radius	1.6[8][a] R☉
Luminosity	16.56[1] L☉
Surface gravity (log g)	4.45[9] cgs
Temperature	8,364[9] K
Metallicity [Fe/H]	+0.14[1] dex
Rotational velocity (v sin i)	44[10] km/s
Age	50[8] Myr
Aa2
Mass	1.47[8] M☉
Radius	1.4[8][a] R☉
Age	50[8] Myr
Ab1
Mass	0.82[8] M☉
Radius	0.86[8][a] R☉
Age	45[8] Myr
Ab2
Mass	0.70[8] M☉
Radius	0.69[8][a] R☉
Age	45[8] Myr
Other designations
Alkarab, υ Oph, 3 Ophiuchi, BD−08°4243, FK5 3299, GC 22134, HD 148367, HIP 80628, HR 6129, SAO 141187, CCDM J16278-0822AB, WDS J16278-0822[11]
Database references
SIMBAD	data

				Aa1
				Period = 27.s d
				Ab2
		Period = 82.8 yr
				Ab1
				Sep = 0.06 au
				Ab2

Hierarchy of orbits^[8]

The variable radial velocity of the brighter component was first observed by H. A. Abt in 1961. It is a double-lined spectroscopic binary system with an orbital period of 27.2 days and an eccentricity of 0.74.^[6] They have a combined magnitude of 4.71. Both components are similar stars with a combined stellar classification of kA2hA5VmA5, and one or both are Am stars.^[3] The fainter component has an 82.8 year orbit with the brighter pair at an eccentricity of 0.45,^[7] and is itself binary, making the system a quadruple.^[8] The system is a source for X-ray emission.^[12]

This system forms part of the Upsilon Ophiuchi cluster, a small group of six stars which share similar kinematics and are spread over about eight degrees. The two brightest stars, apart from Upsilon Ophiuchi itself, are sometimes listed as components B and C: B is HD 148300, and C is HD 144660.^[8] Both are 9th-magnitude K-class dwarfs.^[13]

Notes

1. Calculated using angular diameters (0.37, 0.33, 0.20 and 0.16 milliarcseconds) and a distance of 39.9 parsecs via the equation R/R_☉ = (107.5 • 𝜃 • d)/1000, where 𝜃 is the angular diameter and d is the distance.