An ALMA Study of the FU-Ori Type Object V900 Mon: Implications for the
  Progenitor
  We present ALMA observations of 12CO, 13CO, and C18O J=2--1 lines and the 230
GHz continuum for the FU Ori-type object (FUor) V900 Mon (d~1.5 kpc), for which
the accretion burst was triggered between 1953 and 2009. We identified CO
emission associated with a molecular bipolar outflow extending up to a ~10^4 au
scale and a rotating molecular envelope extending over >10^4 au. The
interaction with the hot energetic FUor wind, which was observed using optical
spectroscopy, appears limited to a region within ~400 au of the star. The
envelope mass and the collimation of the extended CO outflow suggest that the
progenitor of this FUor is a low-mass Class I young stellar object (YSO). These
parameters for V900 Mon, another FUor, and a few FUor-like stars are consistent
with the idea that FUor outbursts are associated with normal YSOs. The
continuum emission is marginally resolved in our observations with a 0."2x0."15
(~300x225 au) beam, and a Gaussian model provides a deconvolved FWHM of ~90 au.
The emission is presumably associated with a dusty circumstellar disk, plus a
possible contribution from a wind or a wind cavity close to the star. The warm
compact nature of the disk continuum emission could be explained with viscous
heating of the disk, while gravitational fragmentation in the outer disk and/or
a combination of grain growth and their inward drift may also contribute to its
compact nature.
