Gamma Andromedae

γ Andromedae is the third brightest star in the constellation Andromeda and is also known as Almach. It is a multiple star system consisting of at least four component stars.

Naming and mythology

Almach, the name being spelled in a variety of ways, derives from the Arabic name of the star, Al ʽAnak al ʽArd, which is a small animal of the weasel family. A subsequent Arabic name for Almach was given as Al Rijl al Musalsalah, indicating Andromeda's foot.

Observational attributes

Almach is a star of apparent magnitude +2.1 at coordinates R.A. 2^h 3^m 54.0^s and Dec. +42° 19ˈ 47ˈˈ. Its parallax of 0.013ˈˈ indicates a distance from Earth of some 250 light years although that may be too small a value.

For the amateur observer γ And. offers a good example of a double stars in which the component stars exhibit contrasting colors.

Physical characteristics

γ Andromedae is a quadruple system composed of the following individual stars:

Component	Magnitude	Spectral class
γ And. A	2.26	K3-IIb
γ And. B	5.1	B8-V
γ And. C	6.3	A0-V
γ And. D

The main component is a giant star with a surface temperature of 4.500 kelvin and an estimated total luminosity of roughly 2.000 times that of the sun. The star is large enough to fill the orbit of Venus if it were in the sun's position.

The secondary star is itself a double system with the stars an average of 0.3ˡˡ apart. The stars orbit each other every 63 years or so. Both stars are main sequence dwarfs. Through spectroscopic observations it was determined that the brighter of these dwarfs is itself also a binary star.