Evidence for episodic warm outflowing CO gas from the intermediate mass
  young stellar object IRAS 08470-4321
  We present a R=10,000 M-band spectrum of LLN19 (IRAS 08470-4321), a heavily
embedded intermediate-mass young stellar object located in the Vela Molecular
Cloud, obtained with VLT-ISAAC. The data were fitted by a 2-slab cold-hot model
and a wind model. The spectrum exhibits deep broad ro-vibrational absorption
lines of 12CO v=1<-0 and 13CO v=1<-0. A weak CO ice feature at 4.67 micron is
also detected. Differences in velocity indicate that the warm gas is distinct
from the cold millimeter emitting gas, which may be associated with the
absorption by cooler gas (45K). The outflowing warm gas at 300-400K and with a
mass-loss rate varying between 0.48E-7 and 4.2E-7 MSun /yr can explain most of
the absorption. Several absorption lines were spectrally resolved in subsequent
spectra obtained with the VLT-CRIRES instrument. Multiple absorption
substructures in the high-resolution (R=100,000) spectra indicate that the
mass-loss is episodic with at least two major events that occurred recently
(<28 years). The discrete mass-loss events together with the large turbulent
width of the gas (dv=10-12 km/s) are consistent with the predictions of the
Jet-Bow shock outflow and the wide-angle wind model. The CO gas/solid column
density ratio of 20-100 in the line-of-sight confirms that the circumstellar
environment of LLN~19 is warm. We also derive a 12C/13C ratio of 67 +/- 3,
consistent with previous measurements in local molecular clouds but not with
the higher ratios found in the envelope of other young stellar objects.
