FS Canis Majoris (FS CMa), also known as HD 45677 or MWC 142, is a B-type

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 ...

Canis Major Canis Major is a constellation in the Southern Celestial Hemisphere, southern celestial hemisphere. In the second century, it was included in Ptolemy's 48 constellations, and is counted among the 88 modern constellations. Its name is Latin fo ...

. It has an apparent visual magnitude of approximately 8.50, having varied between magnitudes 7.35 and 8.58. Feinstein and colleagues reported in 1976 that it had decreased by 0.9 magnitude between 1969 and 1976, whereas it had only varied by 0.3 magnitude in the 70 years beforehand. Sometimes it could vary by up to 0.5 magnitude in a year or 0.1 magnitude in a night, and there did not appear to be any regular period to its variability. Astronomer Anatoly Miroshnichenko has made it the prototype of a new type of variable star, the

FS Canis Majoris variable An FS Canis Majoris variable (FS CMa star) is a type of eruptive variable star. The class of variable stars are named after its prototype, FS Canis Majoris. They are somewhat poorly understood, but are probably binary star systems in which mass e ...

s. These are hot blue-white stars that exhibit

forbidden line In spectroscopy, a forbidden mechanism (forbidden transition or forbidden line) is a spectral line associated with absorption or emission of photons by atomic nuclei, atoms, or molecules which undergo a transition that is not allowed by a particu ...

emission and strong

infra-red Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

excess suggestive of very young (

pre-main-sequence A pre-main-sequence star (also known as a PMS star and PMS object) is a star in the stage when it has not yet reached the main sequence. Earlier in its life, the object is a protostar that grows by acquiring mass from its surrounding envelope of ...

) stars yet they do not lie in star-forming regions. Nor did they appear to be stars that had evolved off the main sequence into giant or supergiant stars. It is now thought that they are main-sequence stars that have absorbed or are absorbing matter, most likely from a companion star, and are surrounded by a compact dusty shell. These stars are thought to be significant contributors to interstellar dust. FS Canis Majoris has been well studied due to its dusty disk, which is inclined 51° relative to the plane of sky. The disk has a gap within 5 au of the star. Its spectral type has been previously classified as B2III to B2V and its bolometric magnitude as -4.89. However, investigation of its spectrum in 2006 showed that FS Canis Majoris is a binary system. The system is between 1,250 and 8,000 times as luminous as the Sun. One calculation has the masses of the primary and secondary at 9.3 ± 0.5 and 4.8 ± 0.9 solar masses and radii 6.6 ± 0.5 and 2.9 ± 0.6 times that of the Sun, and surface temperatures of 21,600 ± 350 and 16,380 ± 1,670 K, respectively.

References

{{DEFAULTSORT:FS Canis Majoris Canis Major B-type main-sequence stars 045677 030800 Canis Majoris, FS FS Canis Majoris variables Shell stars Binary stars Durchmusterung objects