View source for Triggers:FUOri

== 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.

[[File:FUOri.png]]
Plot from [http://www.ta3.sk/caosp/Eedition/FullTexts/vol36no3/pp149-157.pdf D.Chochol et al. 2006].

Characteristics:

* 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) ===

[[File:ExLupi.png|right|400pix|thumb|EX Lupi photometry from Herbig(2007).]]

See Herbig (2007) [http://www.iop.org/EJ/article/1538-3881/133/6/2679/205809.text.html]

* Recurent eruptions
* Amplitudes similar or smaller than in FUors
* Balmer emission lines, He I and other lines as in active T Tauri stars

=== OO Serpentis ===
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 ([http://ukads.nottingham.ac.uk/abs/1996ApJ...468..861H Hodapp et al. 1996]).
It was observed in infrared with ''Infrared Space Observatory'' and Spitzer ([http://arxiv.org/abs/0705.1231 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.