\begin{table}%t1
\caption{\label{tab_lvg}Summary of the $^{13}$CO (2$-$1) and (1$-$0) observations.
  Intensity of the   $^{13}$CO (1$-$0) line ($T_{\rm mb}$) and $^{13}$CO (2$-$1)/(1$-$0) intensity ratio
calculated from the $T_{\rm mb}$ temperatures without any
correction for the different beam sizes. When the  $^{13}$CO (2$-$1) line has not been detected we have used  3$\sigma$~upper limits to  calculate the 2$-$1/1$-$0 ratio. The LVG results for $T_{\rm K}=20$~K are also displayed. 
For the sources where the $^{13}$CO (2$-$1)/(1$-$0) ratio could not be determined, we have assumed a H$_ 2$~density of  $n=10^{3{-}4.5}$~\cmmt. 
The SiO~column density,  $N$(SiO), has been calculated for a H$_2$ density of~$10^{4.5}$~\cmmt .
The SiO~abundance relative to H$_2$, $X$(SiO), has been calculated using a $^{13}$CO abundance
of  $5\times 10^{-6}$  (see text).}
\small%\centering
\par
\begin{tabular}{llllllllll}
\hline\hline\noalign{\smallskip}
 $l $  & $b$   & $v$   & Feature  &     $^{13}$CO (1$-$0)     &   2$-$1/1$-$0  & log($n$(H2)) & $N(^{13}$CO)   & $N$(SiO)          & $X$(SiO)\\
 deg & deg & km~s$^{-1}$ &        &    $T_{\rm mb}$(K)          &             & log(\cmmt) &$10^{16}$ \cmmd & $10^{13}$ \cmmd &  $10^{-9}$   \\
\hline
$ -0.5030$ &$ -0.0500$ &  144.5 & L   & 0.8~$\pm$~0.2 & 0.7~$\pm$~0.4 & ${3.0{-}4.0}$    & 1.1     & $<$$1.1$      & $<$$5$  \\
 $-0.5900$ &$ -0.0500$ &  152.8 & L   & 0.5~$\pm$~0.2 & $<$1.7      & $<$${4.3}$       & 0.38    & $<$$0.8$      & $<$$9.9$ \\
$ -0.6880$ &$ -0.0500 $&  142.5 & L   & 1.0~$\pm$~0.7 & 0.7~$\pm$~0.5 & ${3.{-}3.5}$     & 0.6     & 1.0         & 7.9  \\
  0.9452 & $-0.0500 $&   86.2 & L   & 4.5~$\pm$~0.3 & 1.0~$\pm$~0.1 & ${3.4{-}3.6}$    & 12      & 7.3         & 3.0 \\
  0.1500 &$ -0.0500$ &  154.7 & K   & 1.2~$\pm$~0.1 & 0.6~$\pm$~0.1 & ${3{-}3.5}$      & 0.45    & $<$$0.3$      & $<$$3.1$ \\
  1.3100 & $-0.1300$ &  204.3 & K   & 1.1~$\pm$~0.3 &  ...        & ...            & $2{-}4$     & $<$$0.2$      & $<$$0.33$  \\
  0.3899 & $-0.1500$ &  195.8 & K   & 0.8~$\pm$~0.3 & ...         & ...            & 0.8     & $<$$2.5$      & $<$$15$\\
  1.4027 & $-0.1500$ &  214.3 & K   & 1.0~$\pm$~0.1 & 0.6~$\pm$~0.1 & ${3.{-}3.4}$     &  2      & 0.4         & 0.88\\
  1.5220 &$ -0.1500 $&  219.5 & K   & 1.6~$\pm$~0.3 &  ...        & ...            & 2.5     & 0.2         & 0.4 \\
  0.3899 & $-0.1500$ &  $-92.2$ & M   & 0.5~$\pm$~0.3 & 1.3~$\pm$~0.8 & ${3.5{-}4.3}$    &  $0.2-1$  & 0.3         & $1.3{-}6.8$\\
  0.3899 & $-0.1500 $&  $-71.5$ & M   & 0.3~$\pm$~0.2 & $<$2.3      & $<$${4.3}$       & $>$$0.6$  & 0.6         & $<$$5$\\
  0.9452 &$ -0.0500$ &  $-81.0$ & M   & 1.0~$\pm$~0.3 & 1.0~$\pm$~0.4 & ${3.{-}3.8}$     & 1.1     & 0.7         & 3.2\\
  0.9452 & $-0.0500$ &  $-65.9$ & M   & 1.6~$\pm$~0.3 & 0.7~$\pm$~0.2 & ${3.{-}3.5}$     & 2.8     & 0.4         & 0.63\\
$ -0.6880$ & $-0.0500$ &  $-41.7$ & P   & 0.9~$\pm$~0.4 & 1.5~$\pm$~0.7 & $3.5{-}5 $       & 1.7     & 2.7         & 7.9 \\
 $-0.6880$ & $-0.0500$ &  $-17.5$ & P   & 1.0~$\pm$~0.4 & 2.2~$\pm$~0.9 & ${3.5{-}5}$      & 1.0     & 3.2         & 16 \\
 $-0.6880$ & $-0.0500$ &    2.3 & P   & 2.0~$\pm$~0.4 & 1.5~$\pm$~0.3 & ${3.5{-}5}$      & 1.0     & 5.0         & 25 \\
 $-0.5900$ & $-0.0500$ &  $-41.3$ & P   & 1.6~$\pm$~0.2 & 0.9~$\pm$~0.2 & ${3.5{-}4}$      & 2.2     & $<$$1.4$      & $<$$3.2$  \\
  1.3100 & $-0.1300$ &  $-13.8$ & 1.3 & 2.0~$\pm$~0.3 & 0.8~$\pm$~0.2 & ${3.5{-}4.3}$    & 5.7     & 0.2         & 0.16 \\
  1.3100 & $-0.1300$ &   33.7 & 1.3 & 1.9~$\pm$~0.3 & 1.0~$\pm$~0.2 & ${3.5{-}4.3}$    & 5.7     & 9.5         & 8.3  \\
  1.3100 & $-0.1300$ &   85.0 & 1.3 & 2.4~$\pm$~0.3 & 1.1~$\pm$~0.2 & ${3.5{-}4.3}$    & 7.5     & 5.3         & 3.5  \\
  1.3100 & $-0.1300$ &  135.0 & 1.3 & 0.5~$\pm$~0.3 & $<$1.7      & $<$$10^4$        & 0.4     & $<$$0.1$      & $<$$1.3$  \\
  1.4027 & $-0.1500$ &  $-41.8$ & 1.3 & 1.1~$\pm$~0.1 & 0.6~$\pm$~0.1 & ${3.}$         & 0.6     & $<$$0.1$      & $<$$1.0$ \\
  1.4027 & $-0.1500$ &  $-22.9$ & 1.3 & 1.5~$\pm$~0.3 & 0.7~$\pm$~0.2 & ${3{-}3.5}$      & 1.9     & 0.5         & 1.2\\
  1.4027 & $-0.1500$ &   29.7 & 1.3 & 1.5~$\pm$~0.2 & 0.9~$\pm$~0.2 & ${3.3{-}3.5}$    & $2.2{-}3.5$ & 1.4         & 2.5\\
  1.4027 & $-0.1500 $&   72.3 & 1.3 & 1.6~$\pm$~0.2 & 0.9~$\pm$~0.1 & ${3.3{-}3.5}$    & 6.6     & 2.3         & 1.7 \\
  1.4027 & $-0.1500$ &  123.7 & 1.3 & 0.6~$\pm$~0.0 & 1.3~$\pm$~0.1 & ${3.5{-}4.0}$    & 0.85    & 0.5         & 3\\
  1.5220 & $-0.1500$ &  $-23.4$ & GCR & 1.1~$\pm$~0.8 & 0.8~$\pm$~0.6 & $3.2{-}4$        & 2.3     & 0.5         & 1.0  \\
  1.5220 & $-0.1500$ &   56.0 & GCR & 1.1~$\pm$~0.8 & 0.9~$\pm$~0.7 & $<$$4.3$         & 3.4     & 0.9         & 1.3  \\
 $-0.6880$ & $-0.0500$ & $-129.1$ & GCR & 2.6~$\pm$~0.4 & 1.2~$\pm$~0.2 & $3.5{-}4.5$      & 4.5     & 1.1         & 1.2 \\
 $-0.5900$ & $-0.0500$ &  132.9 & GCR & 0.3~$\pm$~0.0 & $<$3.3      & ...            & 16      & $<$$0.8$      & $<$$0.25$  \\
 $-0.5900$ & $-0.0500$ & $-148.5$ & GCR & 1.1~$\pm$~0.2 & 1.0~$\pm$~0.3 & $3.5{-}4.5$      & 2.5     & $<$$2.6$      & $<$$5.2$ \\
 $-0.5900$ & $-0.0500$ & $-116.7$ & GCR & 5.3~$\pm$~0.2 & 1.0~$\pm$~0.1 & $>$$3.5$         & 9.5     & 3.0         & 1.6 \\
 $-0.5030$ & $-0.0500$ & $-147.4$ & GCR & 1.1~$\pm$~0.2 & 0.6~$\pm$~0.3 & $2.8{-}3.5$      & 0.5     & $0.1{-}0.8$     & $1.3{-}8$ \\
 $-0.5030$ & $-0.0500$ &  $-53.5$ & GCR & 1.0~$\pm$~0.2 & 1.3~$\pm$~0.4 & $3.5{-}4.5$      & 1.4     & $0.7{-}2.1$     & $2.5{-}7.5$ \\
  0.1500 & $-0.0500$ &   25.5 & GCR & 4.0~$\pm$~0.4 & 1.2~$\pm$~0.2 & $>$$3.5$         & 6       & $<$$1$        & 0.79 \\
  0.1500 & $-0.0500$ &   61.1 & GCR & 5.3~$\pm$~0.4 & 1.4~$\pm$~0.1 & $>$$3.5$         & 14      & 1.5         & 0.54 \\
  0.8300 & $-0.1800$ &   31.3 & GCR & 5.0~$\pm$~0.5 & 1.0~$\pm$~0.1 & $>$$3.5$         & 16      & 6.4         & 2  \\
  0.8300 & $-0.1800$ &   56.9 & GCR & 0.5~$\pm$~0.5 & 1.3~$\pm$~1.5 & $3.5{-}4.5$      & 1.1     & 8.5         & 30  \\
  0.8300 & $-0.1800$ &   99.1 & GCR & 1.8~$\pm$~0.5 & 1.0~$\pm$~0.3 & $3.2{-}4.5$      & 1.4     & 1.4         & 5  \\
  0.4100 &  0.0300 &  $-51.0$ & GCR   & 1.1~$\pm$~0.5 & 1.2~$\pm$~0.6 & ${3.5{-}4.2}$    & 1.9     & 2.5         & 6.6\\
  0.4100 &  0.0300 &  $-21.9$ & GCR  & 1.5~$\pm$~0.5 & 0.8~$\pm$~0.3 & ${3.{-}3.5}$     & 3.3     & 1.1         & 1.7 \\
  0.4100 &  0.0300 &   17.0 & GCR & 3.9~$\pm$~0.5 & 1.0~$\pm$~0.2 & $3.5{-}4.3$      & 6.8     & 12          & 8.8 \\
  0.4100 &  0.0300 &   37.9 & GCR & 5.1~$\pm$~0.5 & 1.1~$\pm$~0.1 & $>$$3.5$         & 8.2     & $<$$1.3$      & $< $$0.79$\\
  0.1000 & $-0.1200$ &   $-2.0$ & GCR & 0.8~$\pm$~0.0 & 2.2~$\pm$~0.7 & $>$$3.5$         & 1.1     & 0.9         & 4\\
  0.1000 & $-0.1200$ &   30.1 & GCR & 6.0~$\pm$~0.6 & 1.0~$\pm$~0.2 &  $3.5{-}4.3$     & 25      & 8.2         & 1.64\\
  0.1000 & $-0.1200$ &   68.1 & GCR & 1.9~$\pm$~0.6 & 1.4~$\pm$~0.6 & $>$$3.5$         & 3.8     & 0.9         & 1.2 \\
  0.3899 & $-0.1500$ &  $ -3.5$ & GCR & 1.8~$\pm$~0.2 & 1.5~$\pm$~0.2 & $>$$3.7$         & 1.9     & $<$$0.3$      & $<$$0.7$\\
\hline
\end{tabular}
\end{table}