Astronomy:AN Ursae Majoris

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Short description
Variable star in the constellation Ursa Major
AN Ursae Majoris
Observation data
Equinox J2000.0]] (ICRS)
Constellation Ursa Major
Right ascension  11h 04m 25.65570s[1]
Declination +45 03 13.9415°[1]
Apparent magnitude (V) 14.9 – 20.2[2]
Proper motion (μ) RA: −44.989[1] mas/yr
Dec.: −24.972[1] mas/yr
Parallax (π)3.0993 ± 0.1371[1] mas
Distance1,050 ± 50 ly
(320 ± 10 pc)
Variable type Eclipsing + Polar[2]
Period (P)0.0798 d
Eccentricity (e)0.00
Periastron epoch (T)2,444,217.9961 JD
Argument of periastron (ω)
Semi-amplitude (K1)
321 km/s
White dwarf
Mass0.4–0.6[4] M
Temperature≈ 20,000[4] K
Other designations
AN UMa, PG 1101+453,[5] S 07738, X 11016+454[2]
Database references

AN Ursae Majoris is a binary star[3] system in the northern circumpolar constellation of Ursa Major. It is a variable star, with AN Ursae Majoris being the variable star designation, and ranges in brightness from 14.90 down to 20.2.[2] Even at its peak brightness though, the system is much to faint to be visible to the naked eye. Based on parallax measurements, the system is located roughly 1,050 light years away from the Sun.[1]

This is a single-lined spectroscopic binary system a period of 1.92 hours in a close, circular orbit.[3] The pair form an eclipsing binary system that decreases from magnitude 14.9 down to 20.2, once per orbit.[6] This object, along with AM Herculis, define a class of cataclysmic variables known as polars.[7] The pair consist of a low mass white dwarf with a strong magnetic field, interacting with a low–mass main sequence star that has filled its Roche lobe. Matter is being energetically accreted from the main sequence star onto one or both magnetic poles of the white dwarf star, producing emission lines in the spectrum. The magnetic field of the white dwarf has an estimated strength of 35.8 MG.[4]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode2018A&A...616A...1G.  Gaia DR2 record for this source at VizieR.
  2. 2.0 2.1 2.2 2.3 Samus, N. N. et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1 61 (1): 80–88. doi:10.1134/S1063772917010085. Bibcode2017ARep...61...80S. 
  3. 3.0 3.1 3.2 Schneider, D. P.; Young, P. (September 1980). "VV Puppis and AN Ursae Majoris: a radial velocity study.". Astrophysical Journal 240: 871–884. doi:10.1086/158301. Bibcode1980ApJ...240..871S. 
  4. 4.0 4.1 4.2 Sanad, M. R. (2015). "Ultraviolet spectroscopic investigation of HU Aqr and AN UMa with the data from HST and IUE". Baltic Astronomy 24 (3): 327–341. doi:10.1515/astro-2017-0234. Bibcode2015BaltA..24..327S. 
  5. "AN UMa". SIMBAD. Centre de données astronomiques de Strasbourg. 
  6. Avvakumova, E. A. et al. (October 2013). "Eclipsing variables: Catalogue and classification". Astronomische Nachrichten 334 (8): 860. doi:10.1002/asna.201311942. Bibcode2013AN....334..860A. 
  7. Krzeminski, W.; Serkowski, K. (August 1977). "Extremely high circular polarization of AN Ursae Majoris". The Astrophysical Journal Letters 216: L45. doi:10.1086/182506. Bibcode1977ApJ...216L..45K.