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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]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 11h 41m 03.01594s[1] |
| Declination | +34° 12′ 05.8824″[1] |
| Apparent magnitude (V) | 5.35[2] |
| Characteristics | |
| Evolutionary stage | Main sequence[3] |
| Spectral type | G8V[4] |
| U−B color index | +0.27[5] |
| B−V color index | +0.69[5] |
| Variable type | Suspected |
| Astrometry | |
| Radial velocity (Rv) | −5.18±0.08[6] km/s |
| Proper motion (μ) | RA: −12.247[1] mas/yr Dec.: −381.257[1] mas/yr |
| Parallax (π) | 104.3904 ± 0.1287 mas[1] |
| Distance | 31.24 ± 0.04 ly (9.58 ± 0.01 pc) |
| Absolute magnitude (MV) | 5.53±0.006[7] |
| Details | |
| Mass | 0.93±0.02[8] M☉ |
| Radius | 0.86±0.02[9] R☉ |
| Luminosity | 0.609±0.009[10] L☉ |
| Surface gravity (log g) | 4.54±0.06[3] cgs |
| Temperature | 5,488±44[3] K |
| Metallicity [Fe/H] | −0.03±0.03[3] dex |
| Rotation | 17.1 days[11] |
| Rotational velocity (v sin i) | 3.3[3] km/s |
| Age | 2.1±1.7[8] Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
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]
In the science fiction of Larry Niven's Known Space universe, the homeworld of the major race the Kzinti is the third planet in orbit around 61 Ursae Majoris.[22]
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