3D structure of HII region Sh2-235 from tunable-filter optical
  observations
  We present observations of the H-alpha, H-beta, [SII] 6716, 6731 and [NII]
6583 emission lines in the galactic HII region Sh2-235 with the Mapper of
Narrow Galaxy Lines (MaNGaL), a tunable filter at the 1-m telescope of Special
Astrophysical Observatory of the Russian Academy of Sciences. We show that the
HII region is obscured by neutral material with AV = 2-4 mag. The area with the
highest AV is situated to the south-west from the ionizing star and coincides
with a maximum detected electron density of >=300 cm(-3). The combination of
these results with archive AKARI far-infrared data allows us to estimate the
contribution of the front and rear walls to the total column density of neutral
material in S235, and explain the three-dimensional structure of the region.
The HII region consist of a denser, more compact portion deeply embedded in the
neutral medium and the less dense and obscured gas. The front and rear walls of
the HII region are inhomogeneous, with the material in the rear wall having a
higher column density. We find a two-sided photodissociation region in the
dense clump S235 East 1, illuminated by a UV field with G0=50-70 and 200 Habing
units in the western and eastern parts, respectively.
