\begin{table}%t4
\caption{\label{distances of HII regions}Heliocentric distances for the studied \ion{H}{ii} regions.}%\centerline
{\small
\begin{tabular}{llll}
\hline\hline
\ion{H}{ii} region & $n$ & \multicolumn{2}{c}{$d$ (kpc)}  \\
\cline{3-4} 
\noalign{\smallskip}
                   & & This work     & Literature  \\
\hline
\noalign{\smallskip}
\object{Bran~186} & 1 & $3.05 \pm 1.45$ &           \\
\object{NGC~2626} & 1 & $1.20 \pm 0.34$ & 0.95 [1], 1.25 [2] \\
\object{RCW~32}   & 1 & $0.67 \pm 0.17$ & 0.72 [2], 0.70 [3], 0.77 [4] \\
\object{NGC~3503} & 5 & $2.85 \pm 0.37$ & 2.6 [1], 3.5 [5], 4.2 [6] \\           
\object{RCW~55}   & 7 & $4.36 \pm 0.46$ & 4.3 [7], 3.08 [8] \\
\object{RCW~87}   & 2 & $1.23 \pm 0.30$ & 7.6 [9] \\
\object{RCW~98}   & 3 & $2.61 \pm 0.46$ & 2.87 [2], 3.0 [7], 2.8 [10] \\
\object{RCW~99}   & 2 & $3.55 \pm 1.82$ & 3.54 [7] \\
\object{NGC~6334} & 6 & $1.75 \pm 0.26$ & 2.10 [7], 2.3 [11], 1.74 [12] \\       
\hline
\end{tabular}}
\tablebib{[1] \citet{Herbst 1975},
[2] \citet{Crampton & Fisher 1974},
[3] \citet{Georgelin et al 1973},
[4] \citet{Vogt & Moffat 1975},
[5] \citet{Kharchenko et al 2005},
[6] \citet{Moffat & Vogt 1975},
[7] \citet{Avedisova & Kondratenko 1984},
[8] \citet{Brand & Blitz 1993},
[9] \citet{Borissova et al 2006},
[10] \citet{Yamaguchi et al 1999},
[11] \citet{Walborn 1982},
[12] \citet{Neckel 1978}.}\vspace*{-4mm}
\end{table}