FU Orionis star

One example is the star V1057 Cyg, which became six magnitudes brighter and went from spectral type dKe to F-type supergiant during 1969-1970.

The current model developed primarily by Lee Hartmann and Scott Jay Kenyon associates the FU Orionis flare with abrupt mass transfer from an accretion disc onto a young, low mass T Tauri star.

However, even with such a relatively short timespan, as of 2015[update] no FU Orionis object had been observed shutting off.

By comparing the number of FUor outbursts to the rate of star formation in the solar neighborhood, it is estimated that the average young star undergoes approximately 10–20 FUor eruptions over its lifetime.

The spectra of FU Orionis stars are dominated by absorption features produced in the inner accretion disc.

Short narrated video about the protostar V1647 Orionis and its X-ray emission in 2004.
The blue band light curve for FU Orionis, adapted from Clarke et al. (2005). [ 1 ] The inset plot, adapted from Siwak, et al. (2013), [ 2 ] illustrates the short timescale variability.