Theta Draconis, a name Latinized from θ Draconis, is a

binary star 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 ...

system in the northern circumpolar constellation of Draco. It is faintly visible to the naked eye at night with an apparent visual magnitude of 4.12.

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 place it at an estimated distance of from the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

, and it is drifting closer with a

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

of −8 km/s. It has a relatively high

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 ...

, traversing the

celestial sphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, ...

at the rate of per year. O. J. Eggen included this star as a member of the NGC 1901 supercluster based on its space motion. The binary nature of this system was discovered by W. W. Campbell in 1899, and the first set of

orbital elements Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit. There are many different ways to mathematically describe the same o ...

was published by H. D. Curtis in 1907. It is a single-lined

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 ...

in a close orbit with a period of 3.07 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 ...

(ovalness) of 0.04. The secondary component has been resolved in the

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

H band, allowing an estimation of the mass ratio as . Some velocity variation of K₁ was observed by M. Mayor and T. Mazeh in 1987, which is suggestive of a tertiary component to the system. The primary component is a solar-type star that at various times has been assigned

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 ...

s of F9 V and F8IV-V. The star is about two billion years old and is spinning with a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bu ...

of 31 km/s. It has a high

metallicity In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...

(heavy element abundances) with around 20% more mass than the Sun and nearly three times the Sun's radius. The star displays no chromospheric emission and may be on or entering the subgiant stage. Because of the close orbit, it could be filling up to 60% of its

Roche lobe In astronomy, the Roche lobe is the region around a star in a binary system within which orbiting material is gravitationally bound to that star. It is an approximately teardrop-shaped region bounded by a critical gravitational equipotential, ...

. The star is radiating ten times the luminosity of the Sun 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 .

Chinese name

In Chinese, (), meaning '' Left Wall of Purple Forbidden Enclosure'', refers to an asterism consisting of θ Draconis, ι Draconis, η Draconis, ζ Draconis, υ Draconis,

73 Draconis 73 may refer to: * 73 (number) * One of the years 73 BC, AD 73, 1973, 2073 * 73 (magazine), ''73'' (magazine), a United States-based amateur radio magazine * 73 Best regards, a popular Morse code abbreviations, Morse code abbreviation * ''No. 73'', ...

, γ Cephei and 23 Cassiopeiae. Consequently, the Chinese name for θ Draconis itself is (, .), representing (), meaning ''The First Premier''. 上宰 (Shǎngzǎi) is westernized into ''Shang Tsae'' by R.H. Allen with meaning "the Minor Steward" but it was for η Dra (Aldibain).

References

External links

* {{Sky, 16, 01, 53.35, +, 58, 33, 54.90, 1000000 F-type main-sequence stars Spectroscopic binaries Draco (constellation) Draconis, Theta Durchmusterung objects Draconis, 13 144284 078527 5986