Pi1 Ursae Minoris
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| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Ursa Minor |
| π1 UMi A | |
| Right ascension | 15h 29m 11.18599s[1] |
| Declination | +80° 26′ 54.9713″[1] |
| Apparent magnitude (V) | +6.58[2] |
| π1 UMi B | |
| Right ascension | 15h 29m 23.59426s[1] |
| Declination | +80° 27′ 00.9675″[1] |
| Apparent magnitude (V) | +7.31[2] |
| Characteristics | |
| π1 UMi A | |
| Spectral type | G1.5 V(n)[3] |
| U−B color index | +0.13[2] |
| B−V color index | +0.67[2] |
| π1 UMi B | |
| Spectral type | G9 V[4] |
| U−B color index | +0.37[2] |
| B−V color index | +0.79[2] |
| Astrometry | |
| π1 UMi A | |
| Radial velocity (Rv) | −16.27±0.09[5] km/s |
| Proper motion (μ) | RA: −225.109[6] mas/yr Dec.: +107.575[6] mas/yr |
| Parallax (π) | 45.8577±0.0328 mas[6] |
| Distance | 71.12 ± 0.05 ly (21.81 ± 0.02 pc) |
| Absolute magnitude (MV) | 4.94±0.04[7] |
| π1 UMi B | |
| Radial velocity (Rv) | −15.40±0.70[5] km/s |
| Proper motion (μ) | RA: −217.817[8] mas/yr Dec.: +105.947[8] mas/yr |
| Parallax (π) | 45.8038±0.0352 mas[8] |
| Distance | 71.21 ± 0.05 ly (21.83 ± 0.02 pc) |
| Details | |
| π1 UMi A | |
| Mass | 1.02[9] M☉ |
| Radius | 0.98[6] R☉ |
| Luminosity | 0.929[6] L☉ |
| Surface gravity (log g) | 4.40[10] cgs |
| Temperature | 5,771[10] K |
| Metallicity [Fe/H] | −0.22[11] dex |
| Age | 9.22±3.84[12] Gyr |
| π1 UMi B | |
| Mass | 0.92[9] M☉ |
| Radius | 0.84[8] R☉ |
| Luminosity | 0.520[8] L☉ |
| Surface gravity (log g) | 4.50[10] cgs |
| Temperature | 5,408[10] K |
| Metallicity [Fe/H] | −0.18[11] dex |
| Other designations | |
| π1 UMi, ADS 9696, WDS J15292+8027[13] | |
| π1 UMi A: BD+80°480, HD 139777, HIP 75809, HR 5829, SAO 2556 | |
| π1 UMi B: BD+80°481, HD 139813, HIP 75829, SAO 2558 | |
| Database references | |
| SIMBAD | π1 UMi AB |
| π1 UMi A | |
| π1 UMi B | |
Pi1 Ursae Minoris[14] is a common proper motion binary star[15] system in the northern circumpolar constellation of Ursa Minor. The pair have apparent visual magnitudes of +6.58 and +7.31, with a combined magnitude of 6.1.[2] They are located about 71 light years from the Sun. The two have an angular separation of 31.4 arc seconds,[15] which corresponds to a physical separation of about 680 AU,[16] and orbit each other with a period of about 13,100 years.[9]
Both stars are solar analogs and have been listed as possible members of the Hercules-Lyra association, one of the nearest moving groups to the Sun,[16] although this is now considered unlikely.[17] The primary, π1 Ursae Minoris A, has a mass 2% higher than the sun, an almost identical effective temperature at 5,771 K, a radius 98% of the sun's, and a bolometric luminosity 93% of the sun's. The secondary, π1 Ursae Minoris B, has a mass 92% of the sun's, a slightly lower temperature of 5,408 K, a radius 84% of the sun's, and a luminosity slightly over half of the sun.
