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Eruptive YSOs


FU Oris are an extreme subsample of eruptive classical T Tauri stars. Only one outburst observed, but lasts for decades. Only about a dozen FU Ori bursts observed. FU Ori itself (V1647 Ori) is illuminating a McNeil's nebula in the vicinity of NGC 2068 star-forming region.

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

EX Lupis (EXors) have smaller, shorter, recurrent outbursts

EX Lupi photometry from the ASAS project.

OO Ser was discovered in 1994 and is similar to FUors and EXors, but is so deeply embedded, that at its brightest was not visible in J band (Hodapp et al. 1996). It was observed in infrared with Infrared Space Observatory and Spitzer (Kospal et al. 2007). It has different time scales than FUors and EXors, is rather a fast FUor (similar to V1647 Ori) with a time of rise of about 8 months.


  • diverse zoo of lightcurves
  • many details unknown, unbiased sample required
  • rise time varies from months to years
  • amplitude range from <1 mag to 5 mag
  • outburst last from months to decades
  • extreme events like FU Ori are very rare
  • 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
  • At maximum spectral types are in the range Ae(alpha) - Gpe(alpha)
  • 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)