  FU Orionis stars (FUORS) are eruptive pre-main sequence objects thought to
represent quasi-periodic or recurring stages of enhanced accretion during the
low-mass star-forming process. We characterize the sample of known and
candidate FUORS in an homogeneous and consistent way, deriving stellar and
circumstellar parameters for each object. We emphasize the analysis in those
parameters that are supposed to vary during the FUORS stage. We modeled the
SEDs of 24 of the 26 currently known FUORS, using the radiative transfer code
of Whitney et al (2003b). We compare our models with those obtained by
Robitaille et al. (2007) for Taurus class II and I sources in quiescence
periods, by calculating the cumulative distribution of the different
parameters. FUORS have more massive disks: we find that $\sim80\%$ of the disks
in FUORS are more massive than any Taurus class II and I sources in the sample.
Median values for the disk mass accretion rates are ~ 1.e-7 Msun/yr vs ~ 1.e-5
Msun/yr for standard YSOs (young stellar objects) and FUORS, respectively.
While the distributions of envelope mass accretion rates for class I FUORS and
for standard class I objects are similar, FUORS, on average, have higher
envelope mass accretion rates than standard class II and class I sources. Most
FUORS (~ 70%) have envelope mass accretion rates above 1.e-7 Msun/yr. In
contrast, 60% of the classical YSO sample have accretion rates below this
value. Our results support the current scenario in which changes experimented
by the circumstellar disk explain the observed properties of these stars.
However, the increase in the disk mass accretion rate is smaller than
theoretically predicte (Frank et al. 1992; Hartmann & Kenyon 1996), though in
good agreement with previous determinations.
