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[6] mas
Distance71.12 ± 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[8] mas
Distance71.21 ± 0.05 ly
(21.83 ± 0.02 pc)
Details
π1 UMi A
Mass1.02[9] M☉
Radius0.98[6] R☉
Luminosity0.929[6] L☉
Surface gravity (log g)4.40[10] cgs
Temperature5,771[10] K
Metallicity [Fe/H]−0.22[11] dex
Age9.22±3.84[12] Gyr
π1 UMi B
Mass0.92[9] M☉
Radius0.84[8] R☉
Luminosity0.520[8] L☉
Surface gravity (log g)4.50[10] cgs
Temperature5,408[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
SIMBADπ1 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.

References
  1. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. Johnson, Harold L. (May 1953), "Photoelectric Observations of Visual Double Stars.", Astrophysical Journal, 117: 361, Bibcode:1953ApJ...117..361J, doi:10.1086/145700.
  3. Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637.
  4. Abt, H. A. (1981), "Visual multiples. VII - MK classifications", The Astrophysical Journal Supplement Series, 45: 437, Bibcode:1981ApJS...45..437A, doi:10.1086/190719.
  5. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, A61.
  6. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  7. Porto de Mello, G. F.; et al. (March 2014), "A photometric and spectroscopic survey of solar twin stars within 50 parsecs of the Sun; I. Atmospheric parameters and color similarity to the Sun", Astronomy and Astrophysics, 563: A52, arXiv:1312.7571, Bibcode:2014A&A...563A..52P, doi:10.1051/0004-6361/201322277.
  8. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  9. Tokovinin, Andrei (2014), "From Binaries to Multiples. II. Hierarchical Multiplicity of F and G Dwarfs", The Astronomical Journal, 147 (4): 14, arXiv:1401.6827, Bibcode:2014AJ....147...87T, doi:10.1088/0004-6256/147/4/87, 87.
  10. Mishenina, T. V.; et al. (April 2013), "Abundances of neutron-capture elements in stars of the Galactic disk substructures", Astronomy & Astrophysics, 552: 12, arXiv:1303.1730, Bibcode:2013A&A...552A.128M, doi:10.1051/0004-6361/201220687, A128.
  11. Casagrande, L.; et al. (2011), "New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey", Astronomy & Astrophysics, 530 (A138): 21, arXiv:1103.4651, Bibcode:2011A&A...530A.138C, doi:10.1051/0004-6361/201016276.
  12. Pace, G. (March 2013), "Chromospheric activity as age indicator. An L-shaped chromospheric-activity versus age diagram", Astronomy & Astrophysics, 551: 4, arXiv:1301.5651, Bibcode:2013A&A...551L...8P, doi:10.1051/0004-6361/201220364, L8.
  13. "** STF 1972AB". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-06-26.
  14. Kepple, George Robert; Sanner, Glen W. (1998), The Night Sky Observers Guide: Spring & summer, 2, Willmann-Bell, p. 418, ISBN 0943396603.
  15. Lépine, Sébastien; Bongiorno, Bethany (March 2007), "New Distant Companions to Known Nearby Stars. II. Faint Companions of Hipparcos Stars and the Frequency of Wide Binary Systems", The Astronomical Journal, 133 (3): 889–905, arXiv:astro-ph/0610605, Bibcode:2007AJ....133..889L, doi:10.1086/510333.
  16. Eisenbeiss, T.; et al. (August 2013), "The Hercules-Lyra association revisited. New age estimation and multiplicity study" (PDF), Astronomy & Astrophysics, 556: 19, arXiv:1312.4045, Bibcode:2013A&A...556A..53E, doi:10.1051/0004-6361/201118362, A53.
  17. Lopez‐Santiago, J.; Montes, D.; Crespo‐Chacon, I.; Fernandez‐Figueroa, M. J. (2006), "The Nearest Young Moving Groups", The Astrophysical Journal, 643 (2): 1160–1165, arXiv:astro-ph/0601573, doi:10.1086/503183.
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