Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Chemical evolution in the environment of intermediate mass young stellar
  objects: NGC7129--FIRS2 and LkH$\alpha$234   We have carried out a molecular survey of the Class 0 IM protostar NGC 7129
-- FIRS 2 (hereafter FIRS 2) and the Herbig Be star LkH$\alpha$ 234 with the
aim of studying the chemical evolution of the envelopes of intermediate-mass
(IM) young stellar objects (YSOs). Both objects have similar luminosities (~500
Lsun) and are located in the same molecular cloud which minimizes the chemical
differences due to different stellar masses or initial cloud conditions.
Moreover, since they are located at the same distance, we have the same spatial
resolution in both objects. A total of 17 molecular species (including rarer
isotopes) have been observed in both objects and the structure of their
envelopes and outflows is determined with unprecedent detail.
  Our results show that the protostellar envelopes are dispersed and warmed up
during the evolution to become a pre-main sequence star. In fact, the envelope
mass decreases by a factor >5 from FIRS 2 to LkH$\alpha$234, while the kinetic
temperature increases from ~13K to 28K. On the other hand, there is no
molecular outflow associated with LkH$\alpha$234. The molecular outflow seems
to stop before the star becomes visible. These physical changes strongly affect
the chemistry of their envelopes.
  Based on our results in FIRS2 and LkH$\alpha$ 234, we propose some abundance
ratios that can be used as chemical clocks for the envelopes of IM YSOs. The
SiO/CS, CN/N2H+, HCN/N2H+, DCO+/HCO+ and D2CO/DCO+ ratios are good diagnostics
of the protostellar evolutionary stage.

31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
3
The categories of this paper are: physics
14
The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
30
The categories of this paper are: q-alg
16
The categories of this paper are: stat
13
The categories of this paper are: quant-ph
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The categories of this paper are: funct-an
24
The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
11
The categories of this paper are: hep-lat
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The categories of this paper are: chao-dyn
10
The categories of this paper are: q-bio