Disks and Outflows in CO Rovibrational Emission from Embedded, Low-Mass
  Young Stellar Objects
  Young circumstellar disks that are still embedded in dense molecular
envelopes may differ from their older counterparts, but are historically
difficult to study because emission from a disk can be confused with envelope
or outflow emission. CO fundamental emission is a potentially powerful probe of
the disk/wind structure within a few AU of young protostars. In this paper, we
present high spectral (R=90,000) and spatial (0.3") resolution VLT/CRIRES
M-band spectra of 18 low-mass young stellar objects (YSOs) with dense envelopes
in nearby star-froming regions to explore the utility of CO fundamental 4.6
micron emission as a probe of very young disks. CO fundamental emission is
detected from 14 of the YSOs in our sample. The emission line profiles show a
range of strengths and shapes, but can generally be classified into a broad,
warm component and a narrow, cool component. The broad CO emission is detected
more frequently from YSOs with bolometric luminosities of <15 Lsun than those
with >15 Lsun, and as with CO emission from CTTSs is attributed to the warm
(~1000 K) inner AU of the disk. The CO emission from objects with high
bolometric luminosity is produced in cooler (~320 K), narrow lines in 12CO and
in rarer isotopologues. From some objects, the narrow lines are blueshifted by
up to ~10 km/s, indicating a slow wind origin. For other sources the lines are
located at the systemic velocity of the star and likely arise in the disk. For
a few YSOs, spatially-extended CO and H2 S(9) emission is detected up to 2"
from the central source and is attributed to interactions between the wind and
surrounding molecular material. Warm CO absorption is detected in the wind of
six objects with velocities up to 100 km/s, often in discrete velocity
components. That the wind is partially molecular where it is launched favors
ejection in a disk wind rather than a coronal or chromospheric wind.
