Star formation towards the southern Cometary HII region IRAS 17256-3631
  IRAS 17256-3631 is a southern Galactic massive star forming region located at
a distance of 2 kpc. In this paper, we present a multiwavelength investigation
of the embedded cluster, the HII region, as well as the parent cloud. Radio
images at 325, 610 and 1372 MHz were obtained using GMRT, India while the
near-infrared imaging and spectroscopy were carried out using UKIRT and Mt. Abu
Infrared Telescope, India. The near-infrared K-band image reveals the presence
of a partially embedded infrared cluster. The spectral features of the
brightest star in the cluster, IRS-1, spectroscopically agrees with a late O or
early B star and could be the driving source of this region. Filamentary H_2
emission detected towards the outer envelope indicates presence of highly
excited gas. The parent cloud is investigated at far-infrared to millimeter
wavelengths and eighteen dust clumps have been identified. The spectral energy
distributions (SEDs) of these clumps have been fitted as modified blackbodies
and the best-fit peak temperatures are found to range from 14-33 K, while the
column densities vary from 0.7-8.5x10^22 cm^-2. The radio maps show a cometary
morphology for the distribution of ionized gas that is density bounded towards
the north-west and ionization bounded towards the south-east. This morphology
is better explained with the champagne flow model as compared to the bow shock
model. Using observations at near, mid and far-infrared, submillimeter and
radio wavelengths, we examine the evolutionary stages of various clumps.
