Pi1 Ursae Minoris

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]

For other stars with this Bayer designation, see π Ursae Minoris.

π¹ Ursae Minoris

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

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.