55 Ursae Majoris
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Right ascension 11h 19m 07.89965s[1]
Declination +38° 11′ 08.0285″[1]
Apparent magnitude (V) 4.80[2] (4.78 / 5.3)[3]
Characteristics
Spectral type A2V[2]
(A1V + A2V + A1V)[4]
U−B color index +0.04[5]
B−V color index +0.09[5]
Astrometry
Radial velocity (Rv)-3.0 ± 2[6] km/s
Proper motion (μ) RA: -58.80[1] mas/yr
Dec.: -65.33[1] mas/yr
Parallax (π)17.00 ± 0.34 mas[1]
Distance192 ± 4 ly
(59 ± 1 pc)
Absolute magnitude (MV)-0.09 ± 0.20[4]
Orbit[4]
Primary55 UMa Aa
Companion55 UMa Ab
Period (P)2.5537985 d
Eccentricity (e)0.323
Periastron epoch (T)2449602.368
Argument of periastron (ω)
(secondary)		116.8°
Semi-amplitude (K1)
(primary)		79.1 km/s
Semi-amplitude (K2)
(secondary)		89.1 km/s
Orbit[4]
Primary55 UMa A
Companion55 UMa B
Period (P)1872.7 ± 7.4 d
Semi-major axis (a)0.0913 ± 0.0009″
Eccentricity (e)0.126 ± 0.008
Inclination (i)64.8 ± 0.8°
Longitude of the node (Ω)130.0 ± 0.8°
Periastron epoch (T)2448805 ± 18
Argument of periastron (ω)
(secondary)		223.9 ± 3.7°
Semi-amplitude (K1)
(primary)		8.4 ± 1.3 km/s
Semi-amplitude (K2)
(secondary)		20.2 ± 6.9 km/s
Details[4]
55 UMa Aa
Mass2.0 M☉
Surface gravity (log g)4.25 cgs
Temperature9230 ± 230 K
Rotational velocity (v sin i)30 ± 4 km/s
55 UMa Ab
Mass1.8 M☉
Surface gravity (log g)4.25 cgs
Temperature8810 ± 250 K
Rotational velocity (v sin i)45 ± 5 km/s
55 UMa B
Mass2.1 M☉
Surface gravity (log g)4.25 cgs
Temperature9290 ± 190 K
Rotational velocity (v sin i)55 ± 5 km/s
Other designations
BD+38 2225, FK5 1293, HD 98353, HIP 55266, HR 4380, SAO 62491
Database references
SIMBADdata

55 Ursae Majoris (55 UMa) is a triple star system in the constellation Ursa Major. Its apparent magnitude is 4.80. Two stars form a close spectroscopic binary with an orbital period of 2.55 days. The third star orbits the central pair every 1873 days.[4] All three stars are A-type main-sequence stars.[4]

References

  1. ^ a b c d e van Leeuwen, F.; et al. (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. S2CID 18759600.
  2. ^ a b "* 55 UMa". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 23 February 2013.
  3. ^ "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Archived from the original on 1 August 2017. Retrieved 24 June 2017.
  4. ^ a b c d e f g Liu, Ning; Gies, Douglas R.; Xiong, Ying; Riddle, Reed L.; Bagnuolo, Jr., William G.; Barry, Donald J.; Ferrara, Elizabeth C.; Hartkopf, William I.; Hooda, Jagbir S.; Mason, Brian D.; McAlister, Harold A.; Roberts, Jr., Lewis C.; Sowers, Jon W. (1997). "Tomographic Separation of Composite Spectra. V. The Triple Star System 55 Ursae Majoris". The Astrophysical Journal. 485 (1): 350–358. Bibcode:1997ApJ...485..350L. doi:10.1086/304418.
  5. ^ a b Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  6. ^ Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Washington. Bibcode:1953GCRV..C......0W.


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