AM Herculis

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AM Herculis
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Hercules
Right ascension 18h 16m 13.33s[1]
Declination +49° 52′ 04.2″[1]
Apparent magnitude (V) 12.30-15.7[2]
Spectral type M4.5[1]
Variable type AM/XRM+E[2]
Radial velocity (Rv) -12[1] km/s
Other designations
AN 1923.0028, GSC 3533.01105, X 18149+498[2]
Database references

AM Herculis is a red dwarf variable star located in the constellation Hercules. This star, along with the star AN Ursae Majoris, is the prototype for a category of cataclysmic variable stars called polars, or AM Her type stars.


AM Herculis and was first cataloged in 1923 by Max Wolf and was listed at the time as Veränderlicher 28.1923, which is now AN 28.1923 in the General Catalogue of Variable Stars. It was observed to be an irregular variable star ranging from 12 to 14 in apparent magnitude.[3] In 1976, the astronomer S. Tapia discovered that light from the star is both linearly and circularly polarized, showing that there was a strong magnetic field surrounding the system and revealing that the system was more complex than previously thought.[4][5][6]

See also[edit]


  1. ^ a b c d "V* AM Her -- Cataclysmic Var. AM Her type". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2009-12-16. 
  2. ^ a b c "Query= AM Her". General Catalogue of Variable Stars. Centre de Données astronomiques de Strasbourg. Retrieved 2009-12-16. 
  3. ^ S. Seliwanow (1923). "Mitteilungen über Veränderliche - Veränderlicher 28.1923 Herculis - M. Wolf - December 1923". Astronomische Nachrichten (in German). 220 (15): 255. Bibcode:1924AN....220..249H. doi:10.1002/asna.19232201505. 
  4. ^ Tapia, S. (March 15, 1977). "Discovery of a magnetic compact star in the AM Herculis/3U 1809+50 system". The Astrophysical Journal Letters. 212: L125–L129. Bibcode:1977ApJ...212L.125T. doi:10.1086/182390. 
  5. ^ Hessman, F.V.; Gansicke, B.T. & Mattei, J.A. (September 2000). "The history and source of mass-transfer variations in AM Herculis". Astronomy & Astrophysics. 361: 952–958. Bibcode:2000A&A...361..952H. 
  6. ^ Krzeminski, W. & Serkowski, K. (August 1977). "Extremely high circular polarization of AN Ursae Majoris". The Astrophysical Journal Letters. 216: L45. Bibcode:1977ApJ...216L..45K. doi:10.1086/182506. 
  • Hellier, C. Cataclysmic Variable Stars: How and Why They Vary, Springer, Praxis Publishing Ltd., Chichester, UK, 2001.
  • Hoffmeister, C., Richter, G., and Wenzel, W., Variable Stars, Springer-Verlag, Berlin, 1985.
  • Liller, W. "The Story of AM Herculis", Sky and Telescope, 53, 351-354, 1977.

External links[edit]