Rho Herculis
Binary star in the constellation Hercules
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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.
 | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| 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]