Psi1 Draconis (ψ1 Draconis, abbreviated Psi1 Dra, ψ1 Dra), also designated 31 Draconis, is a triple star system in the northern constellation of Draco. The system is fairly close, and is located about 75 light-years (23 parsecs) from the Sun, based on its parallax.
Psi1 Draconis was considered a binary star consisting of an F-type subgiant and an F-type main-sequence star, designated Psi1 Draconis A (officially named Dziban, from the traditional name of the system)[1] and Psi1 Draconis B, respectively. In 2015, Psi1 Draconis A was itself found to be a double-lined spectroscopic binary, making the system a triple. The companion to Psi1 Draconis A was designated Psi1 Draconis C by its discoverers.
Also in 2015, Psi1 Draconis B was discovered to be orbited by an exoplanet, designated Psi1 Draconis Bb.
ψ1 Draconis (Latinised to Psi1 Draconis) is the system's Bayer designation and 31 Draconis its Flamsteed designation. The designation of the components – ψ1 Draconis A and B – derives from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[2]
Psi1 Draconis bore the traditional name of Dziban or Dsiban, derived from the Arabic Adh-Dhi'ban, meaning "The two wolves" or "The two jackals".[3] In 2016, the IAU organized a Working Group on Star Names (WGSN)[4] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[5] It approved the name Dziban for the component Psi1 Draconis A on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[1]
In Chinese astronomy, Psi1 Draconis is called 女史, Pinyin: Nǚshǐ, meaning Female Protocol, because this star is marking itself and stands alone in the asterism Female Protocol in the Purple Forbidden enclosure (see Chinese constellation).[6] 女史 (Nǚshǐ) has been Latinised into Niu She by R.H. Allen, meaning "the Palace Governess", or "a Literary Woman".[3]
ψ1 Draconis AC and ψ1 Draconis B are separated by about 31 arcseconds. Only a very small fraction of the orbit has been observed: an orbital period of 10,000 years has been calculated,[7] but it is extremely preliminary and likely to be in high error.
ψ1 Draconis A and C have varying radial velocities in respect to Earth, indicating that there must be orbital motion. The orbital period is estimated to be around 20 years, and the eccentricity must be fairly high, around 0.679.
Psi1 Draconis Bb is a Jupiter-like exoplanet orbiting Psi1 Draconis B, the secondary star. The planet was discovered when periodic Doppler shifts in the star's spectrum revealed the presence of a planet, similar to the spectroscopic binary nature of Psi1 Draconis AC. Its minimum mass is, and it orbits its host star every 8.5 years taking a relatively eccentric orbit.