all its scans, in units of antenna temperature in Kelvin (K). The measurement uncertainty is formed by the statistical errors of the Gaussian fits. Figure \[fig2\] shows one example characterizing our sample of observed sources. The line parameters and continuum temperatures are listed in Table \[Table1\].

![image](W3IRS5_C_RP.eps){width="200pt"} ![image](W3IRS5_Ku_RP.eps){width="200pt"}

Then we used these parameters to calculate optical depths () $$\tau = - \ln(1+T_{L}/(T_{C}+T_{BB}-T_{ex})),$$ where $T_L$ is the observed line temperature, $T_C$ is the continuum temperature, $T_{BB}$ is the 2.7 K background radiation, and $T_{ex}$ is the excitation temperature. We have used the RADEX non-LTE model[^1] (@Van [@der; @Tak2007]) to provide excitation temperatures for our sources (see details in Section 3.2). The apparent maximum optical depths $\tau$, which are the optical depths at the velocities with the most negative (absorption) line temperatures, in the $2_{11}-2_{12}$ transition of H$_2$$^{12}$CO are listed in Table \[Table1\]. In Table \[Table2\], the apparent maximum optical depths of the $1_{10}-1_{11}$ transitions are listed. Finally, we can get with the velocity integrated optical depth the column density, following Wilson et al.(): $$N_1[cm^{-2}] = 1.26 \times 10^{13}T_{ex}\int\tau(V)dV.$$ The radial velocity $V$ is in km s$^{-1}$ and the excitation temperature $T_{ex}$ in K. The numerical coefficient is valid for H$_2$$^{12}$CO; the 