  Location of σ2 Ursae Majoris (circled) | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ursa Major |
| σ2 UMa A | |
| Right ascension | 09h10m 23.538s[1] |
| Declination | +67° 08′ 02.44″[1] |
| Apparent magnitude (V) | +4.813[1] |
| σ2 UMa B | |
| Right ascension | 09h10m 23.508s[1] |
| Declination | +67° 08′ 06.58″[1] |
| Apparent magnitude (V) | +10.26[1] |
| Characteristics | |
| Spectral type | F6IV-V / K2V[2] |
| U−B color index | +0.01[3] |
| B−V color index | +0.48[3] |
| Variable type | Suspected[4] |
| Astrometry | |
| σ2 UMa A | |
| Radial velocity (Rv) | −2.92 ± 0.12[5] km/s |
| Proper motion (μ) | RA: 7.1[1] mas/yr Dec.: −95.1[1] mas/yr |
| Parallax (π) | 49.07 ± 0.37 mas[6] |
| Distance | 66.5 ± 0.5 ly (20.4 ± 0.2 pc) |
| Absolute bolometric magnitude (Mbol) | 3.18[7] |
| σ2 UMa B | |
| Proper motion (μ) | RA: 4.1[1] mas/yr Dec.: −30.0[1] mas/yr |
| Absolute magnitude (MV) | 7.16[7] |
| Orbit[8] | |
| Period (P) | 970 ± 118 yr |
| Semi-major axis (a) | 5.80 ± 0.14″ |
| Eccentricity (e) | 0.801 ± 0.017 |
| Inclination (i) | 145.4 ± 1.5° |
| Longitude of the node (Ω) | 102.1 ± 1.9° |
| Periastron epoch (T) | B 1917.39 ± 0.12 |
| Argument of periastron (ω) (secondary) | 332.4 ± 1.9° |
| Details[7] | |
| σ2 UMa A | |
| Mass | 1.31 M☉ |
| Radius | 1.75 ± 0.07 R☉ |
| Surface gravity (log g) | 4.00 ± 0.10 cgs |
| Temperature | 6276 ± 80 K |
| Metallicity [Fe/H] | −0.03 ± 0.07 dex |
| Rotational velocity (v sin i) | 4.1 ± 0.8 km/s |
| σ2 UMa B | |
| Mass | ~0.73 M☉ |
| Temperature | ~4600 K |
| Other designations | |
BD+67°577, Gl 335, HD 78154, HIP 45038, HR 3616, SAO 14788[4] | |
| σ2 UMa A: TYC 4141-1496-1 | |
| σ2 UMa B: TYC 4141-1496-2 | |
| Database references | |
| SIMBAD | AB |
| A | |
| B | |
Sigma2 Ursae Majoris (σ2 Ursae Majoris, σ2 UMa) is a binary star in the constellationofUrsa Major. Parallax measurements made by the Hipparcos spacecraft put it at a distance of about 66.5 light years (20.4 parsecs) from Earth, making this a fairly nearby system. The primary component has an apparent magnitude of about 4.8,[1] meaning it can be seen with the naked eye (see Bortle scale).
This is a visual binary, meaning that the two components can be resolved, and the orbit is derived from the positions of the two stars. The primary component Sigma2 Ursae Majoris A, is a white-colored F-type subgiant. Its radius is about 1.75 times that of the Sun, and it is 31% more massive.[7] The companion is an orange K-type main-sequence star that is much fainter. The two stars are separated about 4 arcseconds away, and because of their slow orbital motion the orbit is poorly known: estimates of the orbital period range from 970 years[8] to over 1,500 years.[9] There is a third component, designated Sigma2 Ursae Majoris C. Located 205 arcseconds from the primary, it is thought to be a line-of-sight coincidence, and is not related to the system.
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