Semi-amplitude (K2)(secondary) 11.1 ± 0.2 km/s | Magnitude 4.57 Apparent magnitude (V) 4.57 | |
Similar Iota Draconis, Zeta Draconis, Nu Draconis, Sigma Draconis, Beta Draconis | ||
Psi1 Draconis (ψ1 Dra, ψ1 Draconis), also known as 31 Draconis, is a star system in the northern constellation of Draco. The system is fairly close, and is located about 75 light-years (23 parsecs) away, based on its parallax.
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Nomenclature
ψ1 Draconis (Latinised to Psi1 Draconis) is the system's Bayer 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).
Psi1 Draconis bore the traditional name of Dsiban derived from the Arabic Adh-Dhi'ban, meaning "The two wolves" or "The two jackals".
In Chinese astronomy, Psi1 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). 女史 (Nǚshǐ) has been latinised into Niu She by R.H. Allen, meaning "the Palace Governess", or "a Literary Woman".
Properties
Psi1 Draconis is a binary star. It consists of two stars, an F-type subgiant and an F-type main-sequence star, designated Psi1 Draconis A and Psi1 Draconis B, respectively. The two stars are separated by about 31 arcseconds. Only a very small fraction of the orbit has been observed: an orbit of with a period 10,000 years has been calculated, but it is extremely preliminary and likely to be in high error.
More recently, Psi1 Draconis A was found to be a binary itself, making the system a triple. It is a double-lined spectroscopic binary. The two components 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.
Exoplanet
In 2015, the discovery of a gas giant planet in the Psi1 Draconis system was announced. 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 A. Its minimum mass is 1.53 MJ, and it orbits its host star every 8.5 years taking a relatively eccentric orbit.