Pi1 Cygni

Pi¹ Cygni, also named Azelfafage, is a star in the northern constellation of Cygnus. It is visible to the naked eye, having a combined apparent visual magnitude of 4.66. The distance to this system can be roughly gauged by its annual parallax shift of 1.89 mas, which yields a separation of around 1,700 light years from the Sun, give or take a hundred light years.

Nomenclature

π¹ Cygni is the star's Bayer designation. The designations of the two components as Pi¹ Cygni A and B derive from the convention used by the Washington Multiplicity Catalog for multiple star systems, and adopted by the International Astronomical Union.
It bore the traditional name Azelfafage, derived from the Arabic al-sulaḥfāh, the tortoise, originally a name for Lyra that was misattributed to a star in Cygnus. R. H. Allen's 1899 book Star Names incorrectly states that the name is derived from ظلف الفرس Dhilf al-faras meaning "the horse track" or ذيل الدجاجة Dhail al-dajāja^h meaning "the tail of the hen". In 2016, the IAU organized a IAU [Working Group on Star Names|Working Group on Star Names] to catalogue and standardize proper names for stars. The WGSN approved the name Azelfafage for Pi¹ Cygni on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.
In Chinese, 螣蛇, meaning Flying Serpent, refers to an asterism consisting of Pi¹ Cygni, Alpha Lacertae, 4 Lacertae, Pi² Cygni, HD 206267, Epsilon Cephei, Beta Lacertae, Sigma Cassiopeiae, Rho Cassiopeiae, Tau Cassiopeiae, AR Cassiopeiae, 9 Lacertae, 3 Andromedae, 7 Andromedae, 8 Andromedae, Lambda Andromedae, Kappa Andromedae, Psi Andromedae and Iota Andromedae. Consequently, the Chinese name for Pi¹ Cygni itself is 螣蛇四.

Properties

Pi¹ Cygni has been described as a single-lined spectroscopic binary with a close, circular orbit, having a period of just 26.33 days. However, a 2020 paper finds no radial velocity variations on the timescale of the published orbit.
The primary, visible, star is a somewhat evolved B-type subgiant star with a stellar classification of B3 IV. It has an estimated 10 times the mass of the Sun and around 5.6 times the Sun's radius. The star radiates 16,538 times the solar luminosity from its outer atmosphere at an effective temperature of roughly 18,360 K. It is about 25 million years old and is spinning with a projected [rotational velocity] of 55 km/s.