天津增六

天鹅座28，又名BD+36 3907，HD 191610、SAO 69518、HR 7708，是天鹅座的一颗恒星，视星等为4.93，位于银经73.91，银纬2.04，其B1900.0坐标为赤经20h 5m 42.7s，赤纬+36° 2.04′ 42″。

28 Cygni is a binary star in the northern constellation of Cygnus. It is a faint blue-white hued star but visible to the naked eye with an apparent visual magnitude of 4.93. The distance to 28 Cyg, as estimated from its annual parallax shift of 3.9 mas, is around 840 light years. It has an absolute magnitude of −2.56, which means that if the star were just 10 parsecs (33 light-years) away it would be brighter than Sirius, the brightest star in the night sky.

This primary object is a B-type main-sequence star with a stellar classification of B2.5 V, per Lesh (1968). Slettebak (1982) found a class of B2 IV(e), which would suggest this is a more evolved subgiant star. It is a Be star, which means the spectrum displays emission lines due a disk of ejected gas in a Keplerian orbit around the star. The star displays short-term variability with two or more periods, and is classified as an SX Arietis variable by Samus et al. (2017). It is spinning rapidly with a projected rotational velocity of 320 km/s; estimated at round 80% of the critical rotation rat…

The companion is a subdwarf O star. After previous failed attempts to find the star, the companion was detected using interferometry. It has an orbital period of nearly a year and is separated by 1.9 astronomical units from its host.