Rho Herculis (ρ Her, ρ Herculis) is a

double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a bi ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

of Hercules. The apparent magnitudes of the components are 4.510 and 5.398, respectively.

Parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

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 . 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 In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

star. Rho Herculis A has been considered to be an Ap star, with unusually strong silicon or mercury and manganese

absorption line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

s in its spectrum, but this is now considered to be dubious.

References

{{DEFAULTSORT:Rho Herculis Hercules (constellation) A-type giants B-type subgiants Double stars Herculis, Rho Herculis, 075 Durchmusterung objects 157778 9 085112 6484 5