The Class 0 Protostar BHR71: Herschel Observations and Dust Continuum
  Models
  We use Herschel spectrophotometry of BHR71, an embedded Class 0 protostar, to
provide new constraints on its physical properties. We detect 645 (non-unique)
spectral lines amongst all spatial pixels. At least 61 different spectral lines
originate from the central region. A CO rotational diagram analysis shows four
excitation temperature components, 43 K, 197 K, 397 K, and 1057 K. Low-J CO
lines trace the outflow while the high-J CO lines are centered on the infrared
source. The low-excitation emission lines of H2O trace the large-scale outflow,
while the high-excitation emission lines trace a small-scale distribution
around the equatorial plane. We model the envelope structure using the dust
radiative transfer code, Hyperion, incorporating rotational collapse, an outer
static envelope, outflow cavity, and disk. The evolution of a rotating
collapsing envelope can be constrained by the far-infrared/millimeter SED along
with the azimuthally-averaged radial intensity profile, and the structure of
the outflow cavity plays a critical role at shorter wavelengths. Emission at
20-40 um requires a cavity with a constant-density inner region and a power-law
density outer region. The best fit model has an envelope mass of 19 solar mass
inside a radius of 0.315 pc and a central luminosity of 18.8 solar luminosity.
The time since collapse began is 24630-44000 yr, most likely around 36000 yr.
The corresponding mass infall rate in the envelope (1.2x10$^{-5}$ solar mass
per year) is comparable to the stellar mass accretion rate, while the mass loss
rate estimated from the CO outflow is 20% of the stellar mass accretion rate.
We find no evidence for episodic accretion.
