Beta Monocerotis (Beta Mon, β Monocerotis, β Mon) is a triple star system in the constellation of

Monoceros Monoceros (Greek: Μονόκερως, "unicorn") is a faint constellation on the celestial equator. Its definition is attributed to the 17th-century Dutch cartographer Petrus Plancius. It is bordered by Orion to the west, Gemini to the north, ...

. To the naked eye, it appears as a single star with an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

of approximately 3.74, making it the brightest visible star in the constellation. A telescope shows a curved line of three pale blue stars (or pale yellow stars, depending on the scope's focus).

William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline ...

who discovered it in 1781 commented that it is "one of the most beautiful sights in the heavens". The star system consists of three

Be stars Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer e ...

, β Monocerotis A, β Monocerotis B, and β Monocerotis C. There is also an additional

visual companion 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 ...

star that is probably not physically close to the other three stars.

System

The three stars of β Monocerotis lie approximately in a straight line. Component B is 7" from component A, and component C a further 3" away. The stars have a common proper motion across the sky and very similar

radial velocities 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 rate of change of the distance or range between the two points. It is equivalent to the vector projection o ...

. They share a single Hipparcos satellite identifier and are assumed to be at the same distance, around 700 light years based on their parallax. β Monocerotis is classified as a variable star, although it is unclear which of the three components causes the brightness changes. The

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

range is given as 3.77 to 3.84 in the Hipparcos photometric band.

Beta Monocerotis A

Beta Monocerotis A (Beta Mon A, β Monocerotis A, β Mon A) is a Be shell star with a mass of approximately 7

solar masses The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass of ...

and a luminosity of 3,200 times the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

's.

Beta Monocerotis B

Beta Monocerotis B (Beta Mon B / β Monocerotis B / β Mon B) is a

Be star Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer e ...

with a mass of approximately 6.2

and a luminosity of 1,600 times the

's.

Beta Monocerotis C

Beta Monocerotis C (Beta Mon C / β Monocerotis C / β Mon C) is a

with a mass of approximately 6

and a luminosity of 1,300 times the

's. This star was observed to be double in

speckle interferometric Speckle imaging describes a range of high-resolution Astrophotography, astronomical imaging techniques based on the analysis of large numbers of short Exposure (photography), exposures that freeze the variation of Astronomical seeing, atmospheri ...

observations in 1988, but this has not been confirmed by later infrared observations.

Visual companion

The triple star system has a

, ''CCDM J06288-0702D'', which has an

of approximately 12 and is visible approximately 25 arcseconds away from β Monocerotis A. It is probably not physically close to the other three stars, merely appearing next to them in the sky.

Notes

References

{{DEFAULTSORT:Beta Monocerotis Monoceros (constellation) Be stars 4 045725 6 7 Monocerotis, Beta 030867 Monocerotis, 11 BD-06 1574 5 Triple star systems Shell stars 2356 7 8