MS Thanh Dat Hoang & Monthly Discussion

/MS Thanh Dat Hoang & Monthly Discussion

MS Thanh Dat Hoang & Monthly Discussion

Event Details

Speaker: Thanh Dat Hoang & , Chair: Tasha Gautam

Title: Studying physical characteristics of protostar envelopes from TOP100 sample with mid- and high-J CO lines

Most high-mass star forming sites in our galaxy have been identified by the
ATLASGAL submm dust continuum survey. From this survey, the TOP100 sample
which consists of the brightest sources in a range of evolutionary stages
was selected. Thereby, studying the TOP100 sample is a key to probe the
evolutionary sequence of high-mass star formation in our galaxy. The sources
we are asking to observe here are selected from different evolutionary
groups of the TOP100 sample. Throughout the evolutionary sequence of high-
mass star formation, dramatic changes are seen at the warm, dense inner
region of protostar envelopes and associated massive outflows. In order to
probe the warm envelopes, we need access to mid- and high-J CO lines which
require a certain level of temperature and density to be excited and these
conditions are likely to exist in the target envelopes. Those lines are now
accessible with new high frequency receivers at ground-base telescopes as
well as on board of SOFIA. Up to the present, a number of mid- and high-J
lines of CO and its isotopologues, which include CO(11-10), CO(16-15),
13CO(6-5), 13CO(8-7), 13CO(10-9), C18O(6-5), and C18O(9-8), have been
observed. Using RADEX, we have succeeded in finding one-component models
that can produce well line ratios from 13CO and C18O lines.
However, our additional RADEX analyses of high-J CO(11-10) and CO(16-15) transitions
hint at the presence of another hot component. That is consistent with HERSCHEL/PACS
results that there is no single-component model that can fit all the CO lines.
With the higher-J CO line proposed in this proposal and extra modelling,
we would be able to explore the hot CO component.