Theta Ophiuchi, Latinized from θ 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 equatorial

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 ...

. It lies on the "right foot" of the serpent-bearer, just southwest of Kepler's Star, the nova of 1604. This star has an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

of +3.3, making it readily visible to the naked eye. Based upon

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 ...

measurements from the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions and distances of ...

mission, it is roughly from Earth. It is 1.8 degrees south of the ecliptic and therefore subject to lunar

occultation An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks f ...

s and (very rarely) occulted by a planet. The next occultation by a planet will be by Mars on 3 October 2078. Theta Ophiuchi appears to be a triple star system. The brightest component 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 The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

of 56.71 days and an

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

of 0.17. The third component is 5.5 magnitude star with a

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...

of B5. Its

angular separation Angular distance or angular separation is the measure of the angle between the orientation of two straight lines, rays, or vectors in three-dimensional space, or the central angle subtended by the radii through two points on a sphere. When t ...

from the binary pair is 0.15

arcsecond A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...

s. This system is a

proper motion Proper motion is the astrometric measure of changes in the apparent places of stars or other celestial objects as they move relative to the center of mass of the Solar System. It is measured relative to the distant stars or a stable referenc ...

member of the Upper Scorpius sub-group in the Scorpius–Centaurus OB association, the nearest such co-moving association of massive stars to the Sun. ThetaOphLightCurve

The primary component of this system is a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

of the Beta Cephei type with a period of just 3h 22m. It has an estimated 8.0 to 8.6 times the mass of the Sun and 4.98 to 5.23 times the Sun's radius. Although only 15.8 to 24 million years old, it has begun to evolve away from the

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

and has become a

subgiant star 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 of ...

with a

of B2 IV. This massive star is radiating between 4,740 and 6,230 times the

luminosity of the Sun The solar luminosity () is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal s ...

from its

photosphere The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...

at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of about 22,260 K, giving it the blue-white hue of a B-type star. According to Richard H. Allen's '' Star Names: Their Lore and Meaning'' (1899), θ Oph together with ξ Oph formed the Sogdian ''Wajrik'' "the Magician", the Khorasmian ''Markhashik'' "the Serpent-bitten" and with η Oph the Coptic ''Tshiō'', "the Snake", and ''Aggia'', "the Magician". With ζ Oph, η Oph, and ξ Oph it formed the Persian ''Garafsa'', the Serpent-tamer; a 1971 NASA list of star names includes the name Garafsa for θ Oph.

References

{{DEFAULTSORT:Theta Ophiuchi B-type subgiants Beta Cephei variables 3 Upper Scorpius Ophiuchi, Theta Ophiuchus CD-24 13292 Ophiuchi, 42 157056 084970 6453