\begin{table}%t2
\caption{\label{tab:te}Electron temperatures calculated using data from the literature.}
\small \begin{tabular}{rrlrrl}
\hline\hline \noalign{\smallskip}
Ratio & $T_{\rm e}$ (K) & Ref./Region &  Ratio & $T_{\rm e}$ (K) & Ref./Region \\
\noalign{\smallskip} \hline
\noalign{\smallskip}
\multicolumn{6}{c}{[\ion{O}{iii}] $(\lambda4959+\lambda5007)/\lambda4363$} \\
\noalign{\smallskip} \hline \noalign{\smallskip}
 99.8 & 12~875 & [1]      & 105.1 & 12~625 & [2]      \\
107.4 & 12~519 & [3]      & 110.9 & 12~370 & [4] NW   \\
117.9 & 12~091 & [4] SE   &  96.6 & 13~044 & [5] I    \\
 96.7 & 13~040 & [5] II   &  90.1 & 13~520 & [6] 1--1c \\
 92.6 & 13~263 & [6] 1--2b & 130.3 & 11~665 & [6] 2--1c \\
113.3 & 12~245 & [6] 2--2b &  85.7 & 13~689 & [7] 1    \\
 92.4 & 13~279 & [7] 2    & 108.7 & 12~464 & [7] 3    \\
 98.5 & 12~942 & [7] 4    &  87.2 & 13~590 & [7] 5    \\ 
114.6 & 12~220 & [7] 11   & 113.2 & 12~275 & [7] 12   \\
111.1 & 12~363 & [7] 13   & 108.0 & 12~492 & [7] 14   \\
105.5 & 12~606 & [7] 15   &  99.1 & 12~916 & [7] 16   \\
 95.3 & 13~113 & [7] 17   &  89.1 & 13~472 & [7] 18   \\
108.2 & 12~487 & [8] \\
\noalign{\smallskip}
\hline
\multicolumn{6}{c}{
[\ion{N}{ii}] $(\lambda6548+\lambda6583)/\lambda5755$ 
} \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
 52.22 & 13~510 & [8] \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
\multicolumn{6}{c}{
[\ion{O}{ii}] $(\lambda3726+\lambda3729)/(\lambda7320+\lambda7330)$ 
} \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
40.8 & 11~627 & [5] I  & 35.5 & 12~747 & [5] II \\
43.0 & 11~707 & [7] 1  & 45.6 & 11~305 & [7] 2  \\
35.4 & 13~324 & [7] 3  & 35.7 & 13~262 & [7] 4  \\
45.8 & 11~263 & [7] 5  & 51.8 & 10~501 & [7] 11 \\
41.5 & 11~974 & [7] 12 & 37.7 & 12~768 & [7] 13 \\
34.0 & 13~731 & [7] 14 & 24.9 & 17~902 & [7] 15 \\
32.7 & 14~125 & [7] 16 & 42.6 & 11~773 & [7] 17 \\
33.7 & 13~813 & [7] 18 & 36.7 & 12~459 & [8]    \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
\multicolumn{6}{c}{
[\ion{S}{ii}] $(\lambda6716+\lambda6731)/(\lambda4068+\lambda4076)$ 
} \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
15.2 & 8~613 & [7] 12 & 15.5 &  8~525 & [7] 13 \\
14.0 & 9~110 & [7] 17 & 10.8 & 10~792 & [8]    \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
\end{tabular}
\begin{minipage}[t]{\columnwidth}
References:
[1] Aller \& Faulkner (\cite{Aller1962}); [2] Dickel et~al. (\cite{Dickel1964}); [3]~Dufour (\cite{Dufour1975}); [4]~Dufour \& Harlow (\cite{Dufour1977}); [5]~Peimbert \& \mbox{Torres-Peimbert} (\cite{Peimbert1976}); [6]~Pagel et~al. (\cite{Pagel1978}); [7]~Peimbert et~al. (\cite{Peimbert2000}); [8]~Tsamis et~al. (\cite{Tsamis2003}).
\end{minipage}
\end{table}