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FU Orionis (FUors)

FU Orionis (V1647 Ori) is young pre-main sequence stars, illuminating a McNeil's nebula in the vicinity of NGC 2068 star-forming region.

FUOri.png Plot from D.Chochol et al. 2006.


  • Very rare
  • Outbursts repeat with a time scale of 40 years (1978, 2003)
  • Amplitude: 5 mag over 4 months
  • Outbursts last for 2 years
  • Spectra: F or G supergiants
  • Spectrum: red, heavily veiled continuum with strong emission of <math>H_{\alpha}</math>; in blue consistent with an early B spectral type
  • X-ray variability present
  • FU Ori and V1057 Cyg rise over 1 yr, whereas V1515 Cyg rise over 20 years
  • FU Ori and V1515 Cyg decline over 20-100 years, V1015 Cyg decays faster (10 yrs)

Similar types to FU Ori

EX Lupis (EXors)

OO Serpentis

OO Ser was discovered in 1995 and is similar to FUors and EXors. It was observed in infrared with Infrared Space Observatory and Spitzer (Kospal et al. 2007).