RR Ursae Minoris
RR Ursae Minoris, or RR UMi, is a binary star system in the northern circumpolar constellation of Ursa Minor. It can be viewed with the naked eye, typically having an apparent visual magnitude of around 4.710. Based upon an annual parallax shift of as seen from Earth's orbit, it is located 330 light years away. The system is moving further from the Sun with a heliocentric radial velocity of +6 km/s.
This is a single-lined spectroscopic binary system with an orbital period of and an eccentricity of 0.13. The a sin i value is, where a is the semimajor axis and i is the orbital inclination to the line of sight from the Earth. The system is a source for X-ray and far-UV emission, with the latter most likely coming from the companion.
The primary component is an aging red giant star on the asymptotic giant branch with a stellar classification of M4.5 III. It is a semiregular variable of subtype SRb, ranging from magnitude 4.44 to 4.85 over a period of 43.3 days. The interferometry-measured angular diameter of the primary component is, which, at its estimated distance, equates to a physical radius of about 103 times the radius of the Sun.
