Mass transport from the envelope to the disk of V346 Nor: a case study
  for the luminosity problem in an FUor-type young eruptive star
  A long-standing open issue of the paradigm of low-mass star formation is the
luminosity problem: most protostars are less luminous than theoretically
predicted. One possible solution is that the accretion process is episodic. FU
Ori-type stars (FUors) are thought to be the visible examples for objects in
the high accretion state. FUors are often surrounded by massive envelopes,
which replenish the disk material and enable the disk to produce accretion
outbursts. However, we have insufficient information on the envelope dynamics
in FUors, about where and how mass transfer from the envelope to the disk
happens. Here we present ALMA observations of the FUor-type star V346 Nor at
1.3 mm continuum and in different CO rotational lines. We mapped the density
and velocity structure of its envelope and analyze the results using channel
maps, position-velocity diagrams, and spectro-astrometric methods. We found
that V346 Nor is surrounded by gaseous material on 10000 au scale in which a
prominent outflow cavity is carved. Within the central $\sim$700 au, the
circumstellar matter forms a flattened pseudo-disk where material is infalling
with conserved angular momentum. Within $\sim$350 au, the velocity profile is
more consistent with a disk in Keplerian rotation around a central star of 0.1
$M_{\odot}$. We determined an infall rate from the envelope onto the disk of
6$\times$10$^{-6}\,M_{\odot}$yr$^{-1}$, a factor of few higher than the
quiescent accretion rate from the disk onto the star, hinting for a mismatch
between the infall and accretion rates as the cause of the eruption.
