TU Muscae

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TU Muscae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Musca
Right ascension 11h 31m 10.92470s [1]
Declination −65° 44′ 32.1019″ [1]

TU Muscae, also known as HD100213, is a star in the constellation Musca. Its apparent magnitude ranges from 8.17 to 8.75 over around 1.4 days.[2]

It is actually a remote binary star system made up of two hot luminous blue main sequence stars of spectral types O7.5V and O9.5V,[1] 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 as their light varies from earth as they eclipse each other.[3] 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 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".[4] The system is thought to be around 4.8 kiloparsecs (~15500 light-years) distant.[3]

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.[5]

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.[6]


  1. ^ a b c d "TU Muscae – Eclipsing Binary of Beta Lyrae type (semi-detached)". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 28 December 2013. 
  2. ^ BSJ (4 January 2010). "TU Muscae". AAVSO Website. American Association of Variable Star Observers. Retrieved 28 December 2013. 
  3. ^ a b Terrell, Dirk; Munari, Ulisse; Zwitter , Tomaˇz; Nelson, Robert H. (2003). "Observational Studies of Early-type Overcontact Binaries: TU Muscae" 126. pp. 2988–96. 
  4. ^ Penny, Laura R.; Ouzts, Cynthia (2008). "Tomographic Separation of Composite Spectra. XI. The Physical Properties of the Massive Close Binary HD 100213 (TU Muscae)". The Astrophysical Journal 681: 554–61. arXiv:0905.3687. Bibcode:2008ApJ...681..554P. doi:10.1086/587509. 
  5. ^ Andersen, J.; Grønbech, B. (1975). "The close 0-type eclipsing binary TU Muscae". Astronomy & Astrophysics 45: 107–15. Bibcode:1975A&A....45..107A. 
  6. ^ Qian, S.-B.; Yuan, J.-Z.; Liu, L.; He, J.-J.; Fernández Lajús, E.; Kreiner, J. Z. (2007). "Evolutionary states of the two shortest period O-type overcontact binaries V382 Cyg and TU Mus". Monthly Notices of the Royal Astronomical Society 380: 1599–1607. Bibcode:2007MNRAS.380.1599Q. doi:10.1111/j.1365-2966.2007.12184.x.