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.
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. 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 .[1]
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.[2] Rho Herculis A has been considered to be an Ap star, with unusually strong silicon or mercury and manganese absorption lines in its spectrum,[3] but this is now considered to be dubious.[4]