Mu Andromedae
Mu Andromedae is a binary star system in the northern constellation of Andromeda. Its Bayer designation is Latinized from μ Andromedae, and abbreviated Mu And or μ And, respectively. The system has an apparent visual magnitude of 3.87, making it readily visible to the naked eye. Based upon parallax measurements, it is located at a distance of approximately from Earth. In the constellation, the star is situated about halfway between the bright star Mirach to the southwest and the Andromeda Galaxy to the northeast.
The spectrum of this star matches a stellar classification of A5 V, indicating that it is an A-type main sequence star. It has 2.2 times the mass of the Sun and three times the Sun's radius. The star is radiating about 40 times the luminosity of the Sun from its outer envelope at an effective temperature of 8,320 K, giving it the characteristic white glow of an A-type star. It is estimated to be about 724 million years old, with a relatively high projected rotational velocity of 75 km/s.
In 2007, Mu Andromedae was found to be a tidally-locked close binary system with an unseen companion. The two stars orbit each other every 550.7 days. The tidal interactions have spun up the primary star, causing it to become magnetically active and host unusually strong starspots.