An ALMA Study of the FU Ori–type Object V900 Mon: Implications for the Progenitor

We present ALMA observations of (CO)-C-12, (CO)-C-13, and (CO)-O-18 J=2-1 lines and the 230 GHz continuum for the FU Ori-type object (FUor) V900 Mon (d similar to 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 an similar to 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 similar to 400 au of the star. The envelope mass and 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 (similar to 300 x 225 au) beam, and a Gaussian model provides a deconvolved FWHM of similar to 90 au. The emission is presumably associated with a dusty circumstellar disk, plus a possible contribution from a wind or 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.