AM Herculis is a
binary variable star located in the
constellation
A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.
The origins of the e ...
Hercules. This star, along with the star ''
AN Ursae Majoris
AN Ursae Majoris is a binary star 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. Eve ...
'', is the prototype for a category of
cataclysmic variable stars called ''
polars'', or ''AM Her'' type stars.
History
AM Herculis was first cataloged in 1923 by
Max Wolf
Maximilian Franz Joseph Cornelius Wolf (21 June 1863 – 3 October 1932) was a German astronomer and a pioneer in the field of astrophotography. He was the chairman of astronomy at the University of Heidelberg and director of the Heidelberg-K� ...
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.
[ 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.][
]
System
The AM Herculis binary system contains a white dwarf and a red dwarf
''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...
. The white dwarf is accreting material directly from the red dwarf without an accretion disk. The white dwarf primary is highly magnetic and the infalling material is channelled towards the magnetic poles. The accretion rate is unstable, at times decreasing dramatically and reducing the brightness of the whole system. There are also periodic variations thought to be caused by the appearance and eclipse of the accreting regions during rotation of the white dwarf.[
]
References
Further reading
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External links
Variable Star Of The Month
by the American Association of Variable Star Observers
{{DEFAULTSORT:AM Herculis
Hercules (constellation)
Polars (cataclysmic variable stars)
Herculis, AM
M-type main-sequence stars