TU Muscae, also known as HD100213, is an

eclipsing binary A binary star or binary star system is a Star system, system of two 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 ...

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

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 first constellati ...

Musca. Its

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

ranges from 8.17 to 8.75 over around 1.4 days.

Physical description

TU Muscae is a remote

binary star A binary star or binary star system is a system of two stars that are 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 as separate stars us ...

system made up of two hot luminous blue main sequence stars of spectral types O7.5V and O9.5V, with masses 23 and 15 times that of the Sun. The stars are so close that they are in contact with each other ( overcontact binary) and are classed as a

Beta Lyrae variable Beta Lyrae variables are a class of close binary stars. Their total brightness is variable star, variable because the two component stars orbit each other, and in this orbit one component periodically passes in front of the other one, thereby bloc ...

as their light varies from earth as they eclipse each other. The spectra indicate they are hot stars, with surface temperatures of roughly 37200 and 34700 K respectively. They are both still on the

main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...

of star evolution, burning their core hydrogen. Astronomers Laura Penny and Cynthia Ouszt proposed the two were originally more equal in size but as they became close enough so that material from the less massive star began transferring to the more massive star via Roche-lobe overflow. However they concede that figuring out the evolution of interacting massive binary systems is "a little like trying to unspill milk". The system is thought to be around 4.8 kiloparsecs (~15500 light-years) distant. The period of the magnitude change is increasing, and has been calculated as lengthening by 3.46 seconds a century. This could be due to material from the less massive star being transferred to the more massive one, or there could be a third or fourth as yet undetected star in the multiple star system influencing the orbit. These stars have not been seen as they are much less luminous than the two main stars.

Discovery

TU Muscae was discovered by Dutch astronomer Pieter Oosterhoff in 1928. Initially thought to have a spectrum of B3, later observations in the 1960s and early 1970s indicated it was a hotter star than previously thought—with the spectrum lying in the uncommon O-region.

References

{{DEFAULTSORT:TU Muscae Beta Lyrae variables Musca O-type main-sequence stars Spectroscopic binaries Muscae, TU 100213 056196 J11311091-6544322 Durchmusterung objects