Omicron² Eridani

Omicron² Eridani

For Union system info see 40 Eridani

40 Eridani (abbreviated 40 Eri), also designated Omicron² Eridani (ο² Eridani, abbreviated Omicron² Eri, ο² Eri), is a triple star system in the constellation of Eridanus. Based on parallax measurements taken during the Hipparcos mission, it is less than 17 light-years from the Sun.

The primary star of the system, designated 40 Eridani A, formally named Keid /ˈkaɪd/ from the traditional name for the system, is easily visible to the naked eye. It is orbited by a binary pair whose two components are designated 40 Eridani B and C, and which were discovered on January 31, 1783, by William Herschel .:p73 It was again observed by Friedrich Struve in 1825 and by Otto Struve in 1851.

In 1910, it was discovered that although component B was a faint star, it was white in color. This meant that it had to be a small star; in fact it was a white dwarf, the first discovered. Although it is neither the closest white dwarf, nor the brightest in the night sky, it is by far the easiest to observe; it is nearly three magnitudes brighter than Van Maanen's Star (the nearest solitary white dwarf), and unlike the companions of Procyon and Sirius it is not swamped in the glare of a much brighter primary.