Rho Herculis

Rho Herculis (ρ Her, ρ Herculis) is a double star in the constellation of Hercules. The apparent magnitudes of the components are 4.510 and 5.398, respectively. Parallax measurements published in Gaia Data Release 2 put the system at some 360-390 light-years (111-121 parsecs) away.

Rho Herculis

Observation data Epoch J2000      Equinox J2000
Constellation	Hercules
ρ Her A
Right ascension	17h 23m 40.972s[1]
Declination	+37° 08′ 45.33″[1]
Apparent magnitude (V)	4.510[1]
ρ Her B
Right ascension	17h 23m 40.718s
Declination	+37° 08′ 48.44″[1]
Apparent magnitude (V)	5.398[1]
Characteristics
ρ Her A
Spectral type	A0IIIpHgMn[2]
U−B color index	−0.06[3]
B−V color index	+0.00[3]
ρ Her B
Spectral type	B9.5IVn[2]
Astrometry
ρ Her A
Radial velocity (Rv)	−21.0 ± 2[4] km/s
Proper motion (μ)	RA: −38.6[5] mas/yr Dec.: 9.2[5] mas/yr
Parallax (π)	8.3380±0.3358 mas[6]
Distance	390 ± 20 ly (120 ± 5 pc)
ρ Her B
Radial velocity (Rv)	−19.3 ± 2[4] km/s
Proper motion (μ)	RA: −38.6[1] mas/yr Dec.: 9.2[1] mas/yr
Parallax (π)	9.0354 ± 0.1135 mas[7]
Distance	361 ± 5 ly (111 ± 1 pc)
Details
A
Mass	4.00/2.93[8] M☉
Temperature	9,118[6] K
Metallicity [Fe/H]	0.0[9] dex
Rotational velocity (v sin i)	75[10] km/s
B
Mass	3.27[8] M☉
Surface gravity (log g)	3.6[9] cgs
Temperature	8,755[7] K
Rotational velocity (v sin i)	291[10] km/s
Other designations
BD+37°2878, HIP 85112, ADS 10526 AB, CCDM J17236+3708AB
ρ Her A: HD 157779, HR 6485, SAO 66001
ρ Her B: HD 157778, HR 6484, SAO 66000
Database references
SIMBAD	ρ Her
	ρ Her A
	ρ Her B

The two stars of Rho Herculis are separated by four arcseconds, and are known as Rho Herculis A and B, respectively. A is an A-type giant star, while B is a B-type subgiant star.^[2] They are also referred to, rarely, as Rho¹ Herculis and Rho² Herculis. Rho Herculis A is itself a close binary which has been resolved using speckle interferometry, with the two components separated by 0.252″.^[11]

The two visual components have very similar spectral types, between A0 and B9. Rho Herculis A is generally assigned a giant luminosity class, with Rho Herculis B most often considered to be a main sequence star.^[12] Rho Herculis A has been considered to be an Ap star, with unusually strong silicon or mercury and manganese absorption lines in its spectrum,^[2][13] but this is now considered to be dubious.^[14]