61_Ursae_Majoris
61 Ursae Majoris
Star in the Ursa Major constellation
61 Ursae Majoris, abbreviated 61 UMa, is a single[13] star in the northern circumpolar constellation of Ursa Major. It has a yellow-orange hue and is dimly visible to the naked eye with an apparent visual magnitude of 5.35.[2] The distance to this star is 31.2 light years based on parallax,[1] and it is drifting closer with a radial velocity of −5.2 km/s.[6] The star has a relatively high proper motion traversing the sky at the rate of 0.381″ yr−1.[14]
The stellar classification of 61 UMa is G8V,[4] matching a late G-type main-sequence star. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[15] It is considered a solar-type star, having physical properties that make it similar to the Sun.[16] The star has 93%[8] of the mass of the Sun and 86%[9] of the Sun's radius. It is roughly two[8] billion years old and is spinning with a projected rotational velocity of 3.3 km/s,[3] for a period of 17.1 days.[11] The metallicity, or abundance of elements with higher atomic number than helium, appears about the same as in the Sun.[3] The star is radiating 61%[10] of the luminosity of the Sun from its photosphere at an effective temperature of 5,488K.[3]
During the 1950s, Karl Pilowski reported that photographic plates taken of the star appeared to show a variability of 0.2 in magnitude. Follow-up studies initially failed to confirm this variability, and it was found not to be an eclipsing binary based on radial velocity measurements.[17] The star's photosphere is rotating differentially, and the rotation period, typically in the range of 16-18 days, shows a larger difference between different latitudes than for most other stars.[18] It has an active chromosphere that exhibits strong and persistent starspot activity.[9] A flare event was captured in 2013 while the star was being observed by the VATT,[19] and the star has been detected as a source of X-ray emission.[20]
No substellar companions have been observed in orbit around this star, and it appears to lack a dust ring as is found around some comparable stars. A radial velocity survey completed in 2020 has indicated that giant planetary companions are absent.[9] A magnitude 11.35 stellar visual companion was reported by O. Struve in 1850. As of 2015, this star was located at an angular separation of 158.90″ from the brighter star, along a position angle of 86°.[21]