AM Herculis is a red dwarf

Red dwarf

According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....

 variable star

Variable star

A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...

 located in the constellation

Constellation

In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Hercules

Hercules (constellation)

Hercules is a constellation named after Hercules, the Roman mythological hero adapted from the Greek hero Heracles. Hercules was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations today...

. This star, along with the star AN Ursae Majoris

AN Ursae Majoris

AN Ursae Majoris is a variable star in the constellation Ursa Major. This star has the strongest known magnetic field among cataclysmic variables , with a field strength of 230 million gauss . This object, along with AM Herculis, define a class of objects known as polars....

, is the prototype for a category of cataclysmic variable stars called polars

Polar (cataclysmic variable)

A Polar is a type of cataclysmic variable binary star system with a very strong magnetic field.In most cataclysmic variables, matter from a main-sequence companion star is gravitationally stripped by a white dwarf star in the form of an accretion disk. In polar systems, the magnetic field of the...

, or AM Her type stars.

History

AM Herculis and was first cataloged in 1923 by Max Wolf

Max Wolf

Maximilian Franz Joseph Cornelius Wolf was a German astronomer and a pioneer in the field of astrophotography...

 and was listed at the time as Veränderlicher 28.1923, which is now AN

Astronomische Nachrichten

Astronomische Nachrichten , one of the first international journals in the field of astronomy, was founded in 1821 by the German astronomer Heinrich Christian Schumacher. It claims to be the oldest astronomical journal in the world that is still being published...

 28.1923 in the General Catalogue of Variable Stars

General Catalogue of Variable Stars

The General Catalogue of Variable Stars is a list of variable stars. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR and edited by B. V. Kukarkin and P. P. Parenago. Second and third editions were published in 1958 and 1968; the fourth...

. It was observed to be an irregular variable star ranging from 12 to 14 in apparent magnitude

Apparent magnitude

The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

. 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.

External links

• Variable Star Of The Month by the American Association of Variable Star Observers