RR Ursae Minoris

RR Ursae Minoris, abbreviated RR UMi, is a binary star[10] system in the northern circumpolar constellation of Ursa Minor. It can be viewed with the naked eye, typically having an apparent visual magnitude of around 4.710.[8] Based upon an annual parallax shift of 10.0 mas[1] as seen from Earth's orbit, it is located 330 light years away. The system is moving further from the Sun with a heliocentric radial velocity of +6 km/s.[6]

RR Ursae Minoris
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Minor
Right ascension 14h 57m 35.01625s[1]
Declination +65° 55′ 56.9143″[1]
Apparent magnitude (V) 4.44 - 4.85[2]
Characteristics
Spectral type M4.55 III[3]
B−V color index 1.590±0.017[4]
Variable type SRb[5]
Astrometry
Radial velocity (Rv)6.21±0.30[6] km/s
Proper motion (μ) RA: −82.191[1] mas/yr
Dec.: +26.981[1] mas/yr
Parallax (π)10.0206 ± 0.6341[1] mas
Distance330 ± 20 ly
(100 ± 6 pc)
Absolute magnitude (MV)−1.11[4]
Orbit[7]
Period (P)748.9 d
Eccentricity (e)0.13±0.05
Inclination (i)79.6±2.4[8]°
Longitude of the node (Ω)48.0±2.5[8]°
Periastron epoch (T)2,444,419±46 JD
Argument of periastron (ω)
(secondary)		212±22°
Semi-amplitude (K1)
(primary)		8.3±0.3 km/s
Details
Mass1.15±0.1[9] M☉
Radius59.8+15.1
−3.6[1] R☉
Luminosity756.7±54.4[1] L☉
Surface gravity (log g)0.00[10] cgs
Temperature3,464[11] K
Other designations
AAVSO 1456+66, RR UMi, BD+66°878, FK5 554, HD 132813, HIP 73199, HR 5589, SAO 16558[12]
Database references
SIMBADdata

This star was found to have a variable radial velocity by J. H. Moore in 1910. It is a single-lined spectroscopic binary system with an orbital period of 2.05 years and an eccentricity (ovalness) of 0.13. The a sin i value is 84 Gm (0.56 AU),[7] where a is the semimajor axis and i is the orbital inclination to the line of sight from the Earth. This gives a lower bound on the physical size of the orbit. The system is a source for X-ray and far-UV emission, with the latter most likely coming from the companion.[10]

The visible component is an aging red giant star on the asymptotic giant branch[10] with a stellar classification of M4.5 III.[3] It was found to be a variable star by J. Ashbrook in 1946,[13] and is catalogued as a semiregular variable of subtype SRb[5] that ranges from magnitude 4.44 to 4.85 over a period of 43.3 days.[2] However, variations in the period have been observed on a time scale of 30–60 days.[14] The star has 1.15[9] times the mass of the Sun and has expanded to 60 times the Sun's radius.[1] It is radiating 757[1] times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 3,464 K.[11]

References
  1. 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.
  2. Otero, Sebastian Alberto (16 November 2009). "RR Ursae Minoris". AAVSO Website. American Association of Variable Star Observers. Retrieved 18 May 2014.
  3. Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins catalog of revised MK types for the cooler stars". Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
  4. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  5. Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  6. 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. S2CID 59451347. A61.
  7. Batten, A. H.; Fletcher, J. M. (July 1986). "A revised spectroscopic orbit for RR Ursae Minoris". Publications of the Astronomical Society of the Pacific. 98: 647–650. Bibcode:1986PASP...98..647B. doi:10.1086/131808.
  8. Ren, Shulin; Fu, Yanning (March 2013). "Hipparcos Photocentric Orbits of 72 Single-lined Spectroscopic Binaries". The Astronomical Journal. 145 (3): 7. Bibcode:2013AJ....145...81R. doi:10.1088/0004-6256/145/3/81. 81.
  9. Halabi, Ghina M.; Eid, Mounib El (2015). "Exploring masses and CNO surface abundances of red giant stars". Monthly Notices of the Royal Astronomical Society. 451 (3): 2957. arXiv:1507.01517. Bibcode:2015MNRAS.451.2957H. doi:10.1093/mnras/stv1141. S2CID 118707332.
  10. Ortiz, Roberto; Guerrero, Martín A. (2016). "Ultraviolet emission from main-sequence companions of AGB stars". Monthly Notices of the Royal Astronomical Society. 461 (3): 3036. arXiv:1606.09086. Bibcode:2016MNRAS.461.3036O. doi:10.1093/mnras/stw1547. S2CID 118619933.
  11. Soubiran, Caroline; et al. (2016). "The PASTEL catalogue: 2016 version". Astronomy & Astrophysics. 591: A118. arXiv:1605.07384. Bibcode:2016A&A...591A.118S. doi:10.1051/0004-6361/201628497. S2CID 119258214.
  12. "RR UMi". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved September 7, 2018.
  13. Dettmar, R. -J.; Gieseking, F. (December 1983). "The intrinsically variable spectroscopic binary RR UMi". Astronomy and Astrophysics, Supplemental Series. 54: 541–543. Bibcode:1983A&AS...54..541D.
  14. Lloyd, C.; West, K. W. (May 1996). "Observations of Low-amplitude Late-Type Variables". Information Bulletin on Variable Stars. 4335: 1. Bibcode:1996IBVS.4335....1L.
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