2014 Special Seminar:
The structure of the transition from the envelope to the rotationally supported disk, the disk-envelope interface, is poorly studied.
This is due to instrumental limitations and lack of disk detections in early embedded protostellar systems.
To probe this region, both CO isotopologues and freeze-out tracers are needed. VLA1623A is a deeply embedded Class 0 protostar with a confirmed rotationally supported disk extending out to at least 150 AU.
This makes VLA1623A an ideal target to study the disk-envelope interface.
We model ALMA Cycle 0 observations of DCO+ and C18O towards VLA1623A. An analytic model using a simple chemical network coupled with radial density and temperature profiles is used as input for line radiative transfer modelling.
Observations show the DCO+ emission towards VLA1623A to border the C18O emission tracing the disk.
Modelling results indicate that a decrease in temperature is needed to reproduce the observed DCO+ emission, while an increase in density reproduces the C18O emission well.
Our results show that the physical structure of the disk-envelope interface differs from the rest of the envelope, highlighting the drastic impact that the disk has on the envelope and temperature structure. Finally, our results show that DCO+ is an excellent tracer of cold temperature regions.