Rho Ophiuchi

This article is about the star. For the dark cloud star forming region, see Rho Ophiuchi cloud complex.

Rho Ophiuchi (ρ Ophiuchi) is a multiple star system in the constellation Ophiuchus. The central system has an apparent magnitude of 4.63.^[2] Based on the central system's parallax, it is located about 450 light-years distant.^[5] The other stars in the system are slightly farther away.^{[11][clarification needed]}

ρ Ophiuchi

Location of ρ Ophiuchi (circled red)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Ophiuchus
Right ascension	16h 25m 35.11766s[1]
Declination	−23° 26′ 49.8150″[1]
Apparent magnitude (V)	4.63[2]
Characteristics
ρ Oph AB
Spectral type	B2/3V + B2V[3]
U−B color index	−0.56[4]
B−V color index	+0.24[4]
Astrometry
ρ Oph AB
Radial velocity (Rv)	−14.6±1.5[5] km/s
Proper motion (μ)	RA: −5.53 mas/yr[1] Dec.: −21.74 mas/yr[1]
Parallax (π)	7.19±0.13 mas[6]
Distance	451±12 ly (138.2±3.6 pc)[5]
Absolute magnitude (MV)	−2.5±0.3[7]
Orbit[5]
Primary	ρ Oph Aa
Companion	ρ Oph Ab
Period (P)	87.831±0.010 days
Semi-major axis (a)	0.995±0.026 AU
Eccentricity (e)	0.17931±0.00017
Inclination (i)	71.348±0.020°
Longitude of the node (Ω)	303.385±0.034°
Periastron epoch (T)	60101.11 RJD
Argument of periastron (ω) (secondary)	4.80±0.24°
Semi-amplitude (K1) (primary)	55.5±3.6 km/s
Semi-amplitude (K2) (secondary)	65.7±3.6 km/s
Orbit[8]
Primary	ρ Oph A
Companion	ρ Oph B
Period (P)	2,398±326 years
Semi-major axis (a)	4.25±0.79″
Eccentricity (e)	0.675±0.322
Inclination (i)	135.3±6.0°
Longitude of the node (Ω)	77.5±13.5°
Periastron epoch (T)	B 2327±343
Argument of periastron (ω) (secondary)	226.1±15.3°
Orbit[8]
Primary	ρ Oph D
Companion	ρ Oph E
Period (P)	675.5±32.5 years
Semi-major axis (a)	1.01±0.15″
Eccentricity (e)	0.707±0.112
Inclination (i)	134.8±2.7°
Longitude of the node (Ω)	152.7±4.6°
Periastron epoch (T)	B 2008.6±34.2
Argument of periastron (ω) (secondary)	260.4±1.1°
Details[6]
ρ Oph Aa
Mass	9.21±0.79[5] M☉
Radius	4.2±0.3 R☉
Luminosity	4,270+980 −800 L☉
Surface gravity (log g)	4.25±0.25 cgs
Temperature	23,000±1,000 K
Rotation	1.205[9] days
Rotational velocity (v sin i)	206±5 km/s
Age	15±6 Myr
ρ Oph Ab
Mass	7.79±0.70[5] M☉
Radius	3.1±0.2 R☉
Luminosity	1,000+400 −290 L☉
Surface gravity (log g)	4.25±0.25 cgs
Temperature	19,000±1,000 K
Rotational velocity (v sin i)	227±5 km/s
Age	15±6 Myr
ρ Oph B
Mass	8[10] M☉
ρ Oph C
Mass	5[10] M☉
ρ Oph D
Mass	3.06[8] M☉
ρ Oph E
Mass	1.97[8] M☉
Other designations
ρ Oph, 5 Oph, WDS J16256-2327
ρ Oph AB: CD−23°12861, HIP 80473
ρ Oph A: HD 147933, HR 6112, SAO 184382
ρ Oph B: HD 147934, HR 6113, SAO 184381
ρ Oph C: CD−23°12862, HIP 80474, SAO 184383
Database references
SIMBAD	ρ Oph
	ρ Oph A
	ρ Oph B
	ρ Oph C
	ρ Oph D/E

System

Rho Ophiuchi cloud complex (N is up): Antares is the bright star that looks yellow in this image, σ Scorpii is in the red nebula (Sh2-9), and the globular cluster M4 is in between. Rho Ophiuchi is the small group of stars in the blue nebulosity (IC 4604).

The central system is known as Rho Ophiuchi AB. It consists of three blue-colored subgiants or main-sequence stars, designated Rho Ophiuchi Aa, Ab and B, respectively.^[11] Rho Ophiuchi Aa-Ab is a spectroscopic binary with an orbital period of 88 days and an orbital period of 1.1 astronomical units.^[6] Farther away is the B companion, a visual binary whose sky-projected distance from the inner pair appears to be 3.1″, corresponding to a separation of at least 344 AU.^[11] However, the actual separation is larger, and the two take about 2,400 years to complete an orbit.^[8] The two stars dominate the radiation field around the Rho Ophiuchi cloud complex.^[9]

Rho Ophiuchi A emits X-rays, and exhibits strong variability in emission over periods of about 1.2 days, corresponding to its rotation period. The X-ray variability is due to the strong magnetic field of the secondary companion, Rho Ophiuchi Ab, whose dipole strength is 4 kG.^[6][12]

Several other stars are located close to Rho Ophiuchi AB. HD 147932 is located 2.5 arcminutes away (at least 17,000 AU), and is known as Rho Ophiuchi C.^[11] HD 147888 is located 2.82 arcminutes away (at least 19,000 AU), and is known as Rho Ophiuchi DE.^[11] Stars C and D are both B-type main-sequence stars,^[11] and D itself is another binary with an orbital period of around 680 years.^[8]

Cloud complex

Main article: Rho Ophiuchi cloud complex

Rho Ophiuchi is the namesake of the Rho Ophiuchi cloud complex. It is a nebula of gas and dust, which the Rho Ophiuchi system is embedded in. It is one of the easiest star forming regions to observe, as it is one of the nearest, and it is visible from both hemispheres.^[13]

The interstellar extinction (A_V) of Rho Ophiuchi is measured to be 1.45 magnitudes, meaning the dust and gas in front of Rho Ophiuchi absorbs light from the system, making it appear 1.45 magnitudes dimmer than it would be if there were no dust or gas.^[14] Additionally, gas and dust also scatters more higher-frequency light, leaving the light appearing more reddish. The interstellar reddening (E_B−V) of Rho Ophiuchi has been measured to be 0.47 magnitudes.^[7]