Rho Ophiuchi (ρ Ophiuchi) is a

multiple star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally called a ''st ...

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 first constellati ...

Ophiuchus Ophiuchus () is a large constellation straddling the celestial equator. Its name comes from the Ancient Greek (), meaning "serpent-bearer", and it is commonly represented as a man grasping a snake. The serpent is represented by the constellati ...

. The central system has an apparent magnitude of 4.63. Based on the central system's

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

, it is located about 450 light-years distant. The other stars in the system are slightly farther away.

System

The central system is known as Rho Ophiuchi AB. It consists of three blue-colored

subgiant A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...

s or

main-sequence star In astronomy, the main sequence is a classification of stars which appear on plots of stellar color versus brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or dwarf stars, and positions of star ...

s, designated Rho Ophiuchi Aa, Ab and B, respectively. Rho Ophiuchi Aa-Ab is a

spectroscopic binary A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

with an orbital period of 88 days and an orbital period of 1.1

astronomical unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...

s. Farther away is the B companion, a

visual binary A visual binary is a gravitationally bound binary star system that can be resolved into two stars. These stars are estimated, via Kepler's third law, to have periods ranging from a few years to thousands of years. A visual binary consists of two st ...

whose sky-projected distance from the inner pair appears to be 3.1″, corresponding to a separation of at least 344 AU. However, the actual separation is larger, and the two take about 2,400 years to complete an orbit. The two stars dominate the radiation field around the Rho Ophiuchi cloud complex. Rho Ophiuchi A emits

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

s, and exhibits strong variability in emission over periods of about 1.2 days, corresponding to its

rotation period In astronomy, the rotation period or spin period of a celestial object (e.g., star, planet, moon, asteroid) has two definitions. The first one corresponds to the '' sidereal rotation period'' (or ''sidereal day''), i.e., the time that the objec ...

. The X-ray variability is due to the strong

magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

of the secondary companion, Rho Ophiuchi Ab, whose dipole strength is 4 kG. 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. HD 147888 is located 2.82 arcminutes away (at least 19,000 AU), and is known as Rho Ophiuchi DE. Stars C and D are both

B-type main-sequence star A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. B-type stars ...

s, and D itself is another binary with an orbital period of around 680 years.

Cloud complex

Rho Ophiuchi is the namesake of the

Rho Ophiuchi cloud complex The Rho Ophiuchi cloud complex is a complex of interstellar clouds with different nebulae, particularly a dark nebula which is centered 1° south of the star ρ Ophiuchi, which it among others extends to, of the constellation Ophiuchus. At an est ...

. 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. The interstellar extinction (A_''V'') of Rho Ophiuchi is measured to be 1.45

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

s, 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. 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.

References

{{DEFAULTSORT:Rho Ophiuchi Ophiuchus 5 B-type main-sequence stars Ophiuchi, Rho Ophiuchi, 05 Durchmusterung objects 147933 080473 6112