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

binary star A binary star 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 using a telescope as separate stars, in wh ...

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 lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

measurements place it at an estimated distance of from the Sun, and it is drifting closer with a

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

of −8 km/s. It has a relatively high

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

, 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 ...

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

spectroscopic binary A binary star is a system of two star, stars that are gravity, 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 using a telescope as separa ...

in a close orbit with a period of 3.07 days and an eccentricity (ovalness) of 0.04. The secondary component has been resolved in the infrared 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 Solar-type star, solar analogs (also analogues), and solar twins are stars that are particularly similar to the Sun. The stellar classification is a hierarchy with solar twin being most like the Sun followed by solar analog and then solar-typ ...

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 grati ...

s of F9 V and F8IV-V. The star is about two billion years old and is spinning with a projected rotational velocity of 31 km/s. It has a high

metallicity In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...

(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. 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. The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...

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,

γ Cephei Gamma Cephei (γ Cephei, abbreviated Gamma Cep, γ Cep) is a binary star system approximately 45 light-years away in the constellation of Cepheus. The primary (designated Gamma Cephei A, officially named Errai , the traditional name of ...

and

23 Cassiopeiae 3 (three) is a number, numeral and digit. It is the natural number following 2 and preceding 4, and is the smallest odd prime number and the only prime preceding a square number. It has religious or cultural significance in many socie ...

. Consequently, the Chinese name for θ Draconis itself is (, en, the Second Star of Left Wall of Purple Forbidden Enclosure.), 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