BX Trianguli
BX Trianguli is a binary system made up of two red dwarfs, in the constellation Triangulum. Both stars eclipse each other and have an orbital period of four hours and 40 minutes. They are located at around 170 light-years from Earth based upon parallax measurements.
Variability
This is an eclipsing binary variable, first identified by the Northern Sky Variability Survey survey in 2004 and given its variable-star designation BX Trianguli in 2010. Both stars in the system eclipse each other as seen from Earth, causing the brightness of the system to drop from a magnitude of 12.35 to 12.6/12.7 on the secondary/primary ecplise respectively.The system has also been identified as a flare star. Six flares were recorded between 2014 and 2017, the strongest being identified in November 2014, four times stronger than a typical superflare. The large occurrence of flares on BX Trianguli is the highest among eclipsing binaries after Castor C and might be related to rapid mass transfer between the components. These flares likely occur on BX Trianguli B.
BX Trianguli also has strong magnetic activity, manifested as starspots on the primary's surface and Hα emission.
Characteristics
This system is composed of two red dwarfs, which have an ultra-short period of just hours and a separation of 1.33 solar radii, or two and a half times the distance to the Moon. This orbit is one of the shortest known among main sequence stars. The primary star, named BX Trianguli A, has a mass equivalent to 58% the solar mass and a radius equivalent to 60% of the solar radius, while the secondary BX Trianguli B is smaller, at 28% and 27% of the solar mass and radius respectively. BX Trianguli has a semi-detached configuration, with the "A" component being distorted due to gravitational interactions with its partner.There is a star that could be bound to this system, called USNO-B1 1233−0046425, at roughly 3500 astronomical units of distance.