A CO survey on a sample of Herschel cold clumps
  The physical state of cold cloud clumps has a great impact on the process and
efficiency of star formation and the masses of the forming stars inside these
objects. The sub-millimetre survey of the Planck space observatory and the
far-infrared follow-up mapping of the Herschel space telescope provide an
unbiased, large sample of these cold objects. We have observed $^{12}$CO(1$-$0)
and $^{13}$CO(1$-$0) emission in 35 clumps in 26 Herschel fields sampling
different environments in the Galaxy. Densities and temperatures were
calculated from both the dust continuum and the molecular line data, kinematic
distances were derived using $^{13}$CO line velocities and clump sizes and
masses were calculated by fitting 2D Gaussian functions to the optical depth
distribution maps. Clump masses and virial masses were estimated assuming an
upper and lower limit on the kinetic temperatures and considering uncertainties
due to distance limitations. The excitation temperatures are between 8.5$-$19.5
K, while the Herschel-derived dust colour temperatures are 12$-$16 K. The sizes
(0.1$-$3 pc), $^{13}$CO column densities (0.5$-$44$\times$10$^{15}$ cm$^{-2}$)
and masses (from less than 0.1 $M_{\odot}$ to more than 1500 $M_{\odot}$) of
the objects span broad ranges. Eleven gravitationally unbound clumps were
found, many of them smaller than 0.3 pc, but large, parsec-scale clouds with a
few hundred solar masses appear as well. Colder clumps have generally high
column densities but warmer objects appear at both low and higher column
densities. The clump column densities derived from the line and dust
observations correlate well, but are heavily affected by uncertainties of the
dust properties, varying molecular abundances and optical depth effects.
