1 Geminorum (1 Gem) is a
star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
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 ...
Gemini. Its
apparent magnitude is 4.15.
In the 19th century,
John Flamsteed numbered the brighter stars, by constellation, from west to east, and 1 Geminorum was the first star listed in Gemini. It is also listed in the
Bright Star Catalogue as star 2134, usually designated HR 2134 with the HR standing for the
Harvard Revised catalog, the precursor to the Bright Star Catalogue.
In 1948, 1 Geminorum was discovered to be a close
double star
In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes.
This occurs because the pair either forms a binary star (i.e. a bi ...
whilst using it to focus a telescope for observations of the planet
Uranus. From initial observations of the
spectrum, it was estimated that both components were giants and that the secondary was itself double.
Radial velocity
The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...
variations had been found in 1906, but only one set of
absorption line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...
s could be detected in the spectrum and it was not possible to calculate a reliable orbit until 1976.
1 Geminorum is a
triple star system 0.17 degree south of the ecliptic. The primary component of the system, 1 Geminorum A, is a
K-type red clump giant star around twice the mass of the
Sun.
Component A is orbited by a
spectroscopic binary
A binary star is a system of two star, stars that are gravity, gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separa ...
pair of stars at a separation of about 9.4
astronomical units every 4877.6 days. The two secondary components, 1 Geminorum Ba and Bb, have not been resolved, but regular periodic
Doppler shift
The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...
s in the spectrum indicate orbital motion of a binary pairing consisting of an
F-type subgiant and a solar-mass star that may be
G-type, separated by approximately 0.1234 astronomical units.
[
In 1893, a 14th magnitude companion was reported by Sherburne Wesley Burnham from the naked-eye star,]
References
{{DEFAULTSORT:1 Geminorum
Gemini (constellation)
K-type giants
Geminorum, 01
Spectroscopic binaries
Triple star systems
Durchmusterung objects
041116
028734
2134
In contemporary history, the third millennium of the anno Domini or Common Era in the Gregorian calendar is the current millennium spanning the years 2001 to 3000 ( 21st to 30th centuries). Ongoing futures studies seek to understand what is l ...
Suspected variables
F-type subgiants
G-type main-sequence stars