- CO abundances in a protostellar cloud: freeze-out and desorption in the envelope and outflow of L483
CO isotopes are able to probe the different components in protostellar clouds. These components, core,
envelope and outflow have distinct physical conditions, and sometimes more than one component
contributes to the observed line profile. In this study, we determine how CO isotope abundances
are altered by the physical conditions in the different components. We use a 3D molecular line
transport code to simulate the emission of four CO isotopomers,
12CO J = 2 -> 1, 13CO J = 2 -> 1, C18O J = 2 -> 1 and C17O J = 2 -> 1 from the Class 0/1 object L483,
which contains a cold quiescent core, an infalling envelope and a clear outflow.
Our models replicate James Clerk Maxwell Telescope (JCMT) line observations with the inclusion of
freeze-out, a density profile and infall. Our model profiles of 12CO and 13CO have a
large linewidth due to a high-velocity jet. These profiles replicate the process of more
abundant material being susceptible to a jet. C18O and C17O do not display such a large
linewidth as they trace denser quiescent material deep in the cloud.
Patrick B. Carolan, Matthew P. Redman, Eric Keto & Jonathan M.C. Rawlings, 2008, MNRAS, 383, 705
- Radiative Transfer and Starless Cores
We develop a method of analyzing radio-frequency spectral line observations to derive
data on the temperature, density, velocity, and molecular abundance of the emitting gas.
The method incorporates a radiative transfer code with a new technique for handling
overlapping hyperfine emission lines within the accelerated -iteration algorithm and a
heuristic search algorithm based on simulated annealing. We apply this method to new
observations of N2H+ in three Lynds clouds thought to be starless cores in the first
stages of star formation and determine their density structure. A comparison of the gas
densities derived from the molecular line emission and the millimeter dust emission
suggests that the required dust mass opacity is about 1.3mm=0.04 cm^2/g, consistent with
models of dust grains that have opacities enhanced by ice mantles and fluffy aggregrates.
Eric R. Keto, George B. Rybicki, Edwin A. Bergin & Rene Plume, 2004, ApJ, 613, 355
- Radiative transfer modeling of radio-frequency spectral line data - Accretion onto G10.6 - 0.4
This paper describes a procedure for simulating spectral line images of three-dimensional
molecular clouds. It is suggested that this technique can be useful in the more general
problem of determining the three-dimensional structure of molecular clouds. The technique
is demonstrated by comparing observed and simulated images of the accretion flow associated
with high-mass star formation in the region G10.6 - 0.4. As a result of the comparison,
the temperature, density, and velocity fields are described, and a vector map of the
accretion flow direction and magnitude is presented. The results indicate that the molecular
cloud core is strongly condensed and has approximately equal velocities in rotation and
infall at its current evolutionary state. The rapid collapse and lack of rotational
support suggests that significant angular momentum transfer is occurring over scales
at least as large as those observed (0.5 pc). A milligauss magnetic field would have
sufficient energy to supply the required braking torque of 10 to the 47th ergs.
Eric R. Keto 1990, ApJ, 355, 1990