In stellar evolution, FU Orionis stars are pre-main sequence stars which display an extreme change in magnitude and spectral type. One example is the star V1057 Cyg, which became 6 magnitudes brighter and went from spectral type dKe to F supergiant. In astronomy, stellar evolution is the sequence of changes that a star undergoes during its lifetime, the millions or billions of years during which it emits light and heat. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequenly refined in terms of other characteristics. ...
The current model associates the FU Orionis flare with abrupt disk accretion onto a young, low mass T Tauri star. T Tauri stars are a class of variable stars named after their prototype T Tauri. ...
The prototypes of this class are: FU Ori (http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=FU+Ori&NbIdent=1&Radius=10&Radius.unit=arcmin&CooFrame=FK5&CooEpoch=2000&CooEqui=2000&output.max=all&o.catall=on&output.mesdisp=N&Bibyear1=1983&Bibyear2=2005&Frame1=FK5&Frame2=FK4&Frame3=G&Equi1=2000.0&Equi2=1950.0&Equi3=2000.0&Epoch1=2000.0&Epoch2=1950.0&Epoch3=2000.0), V1057 Cyg (http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=V1057+cyg&NbIdent=1&Radius=10&Radius.unit=arcmin&CooFrame=FK5&CooEpoch=2000&CooEqui=2000&output.max=all&o.catall=on&output.mesdisp=N&Bibyear1=1983&Bibyear2=2005&Frame1=FK5&Frame2=FK4&Frame3=G&Equi1=2000.0&Equi2=1950.0&Equi3=2000.0&Epoch1=2000.0&Epoch2=1950.0&Epoch3=2000.0) and V1515 Cyg (http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=V1515+Cyg&NbIdent=1&Radius=10&Radius.unit=arcmin&CooFrame=FK5&CooEpoch=2000&CooEqui=2000&output.max=all&o.catall=on&output.mesdisp=N&Bibyear1=1983&Bibyear2=2005&Frame1=FK5&Frame2=FK4&Frame3=G&Equi1=2000.0&Equi2=1950.0&Equi3=2000.0&Epoch1=2000.0&Epoch2=1950.0&Epoch3=2000.0); being the more recent addition the embedded protostar V1647 Ori (http://simbad.u-strasbg.fr/sim-id.pl?protocol=html&Ident=V1647+Ori&NbIdent=1&Radius=10&Radius.unit=arcmin&CooFrame=FK5&CooEpoch=2000&CooEqui=2000&output.max=all&o.catall=on&output.mesdisp=N&Bibyear1=1983&Bibyear2=2005&Frame1=FK5&Frame2=FK4&Frame3=G&Equi1=2000.0&Equi2=1950.0&Equi3=2000.0&Epoch1=2000.0&Epoch2=1950.0&Epoch3=2000.0), which erupted in 2004 January. The protostar period is the period in the evolution of a star after the cloud of hydrogen, helium and dust has started contraction and before the star has reached the main sequence on the Hertzsprung-Russell diagram. ...
FUOrionis stars appear to be a stage in the development of T Tauri stars.
They gradually brighten by about six magnitudes over several months, during which time matter is ejected, then remain almost steady or slowly decline by a magnitude or two over a period of years.
All known FU Ori stars (commonly known as fuors) are associated with reflection nebulae.
"The Circumstellar Environment of FUOrionis Stars" Stuart McMuldroch, Ph.D. Thesis (Planetary Science, Prof.
[65] "The FUOrionis Binary System RNO 1B/1C" Stuart McMuldroch, Geoffrey A. Blake, & Anneila I. Sargent 1995, A.J. [66] "Molecular Abundances and Low Mass Star Formation II.
[102] "Far-Infrared Spectroscopy of FU Ori Objects: ISO-LWS Observations" D.
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