Kinematic study of the molecular gas associated with two cometary
  globules in Sh2-236
  Cometary globules, dense molecular gas structures exposed to the UV
radiation, are found inside HII regions. Understanding the nature and origin of
these structures through a kinematic study of the molecular gas is useful to
advance in our knowledge of the interplay between radiation and molecular gas.
Using ASTE we carried out molecular observations towards two cometary globules
(Sim129 and Sim130) in the HII region Sh2-236. We mapped two regions with the
12CO J=3-2 and HCO+ J=4-3 lines. Additionally, two single pointings of C2H
(N=4-3), HNC and HCN J=4-3 were observed. We combined our observations with
public infrared and optical data to analyse the distribution and kinematics of
the gas. We found kinematic signatures of infalling gas in the 12CO J=3-2 and
C2H J=4-3 spectra towards Sim129 . We detected HCO+, HCN, and HNC J=4-3 only
towards Sim130. The HCN/HNC integrated ratio of about 3 found in Sim130
suggests that the possible star formation activity within the globule has not
yet ionized the gas. The location of NVSS 052255+33315, which peaks towards the
brightest border of the globule, supports this scenario. The non-detection of
these molecules towards Sim129 could be due to the radiation arising from the
star formation activity inside this globule. The ubiquitous presence of the C2H
molecule towards both globules shows the action of nearby O-B stars irradiating
their external layers. Based on mid-infrared emission, we identified two new
structures: a region of diffuse emission (R1) located, in projection, in front
of the head of Sim129, and a pillar-like feature (P1) placed besides Sim130.
Based on 12CO J=3-2, we found molecular gas associated with Sim129, Sim130, R1
and P1 at radial velocities of -1.5, -11, +10, and +4 km/s, respectively.
Therefore, while Sim129 and P1 are located at the far side of the shell, Sim130
is placed at the near side, consistent with earlier results.
