Scatter plot from dat file where each mark size depends on 3rd column in table?

Question

I am trying to create a basic scatter plot where each point's mark size has a unique value given by a 3rd column in the dat file. In the code below, mark size should be mediated by the 'Mag' column. For example, if Mag = 0.13, then mark size = 0.13pt. I don't know how to map the 3rd column to mark size. Thanks!

\documentclass[tikz, border=5mm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\usetikzlibrary{plotmarks}
\usepackage{amsmath}
\usepackage{filecontents}
\begin{filecontents}{temp.dat}
RA      DEC     Mag
78.63   -8.20   0.13
88.79   7.41    0.42
81.28   6.35    1.64
84.05   -1.20   1.69
85.19   -1.94   1.77
86.94   -9.67   2.06
83.00   -0.30   2.41
83.86   -5.91   2.77
72.46   6.96    3.19
81.12   -2.40   3.35
83.78   9.93    3.47
79.40   -6.84   3.59
83.78   9.93    3.66
72.80   5.61    3.68
73.56   2.44    3.73
84.69   -2.60   3.79
74.09   13.51   4.06
84.23   9.29    4.09
80.99   -7.81   4.12
90.60   9.65    4.13
82.70   5.95    4.2
72.65   8.90    4.35
91.89   14.77   4.397
88.60   20.28   4.4
83.71   9.49    4.41
78.32   2.86    4.44
74.64   1.71    4.459
92.98   14.21   4.48
83.85   -4.84   4.59
84.80   4.12    4.59
\end{filecontents}
\begin{document}
\pgfplotstableread{temp.dat}{\tempdat}
\begin{tikzpicture}
\begin{axis}
\addplot[%
    only marks,
    mark=*,
] 
table [x={RA},y={DEC}] {\tempdat};
\end{axis}
\end{tikzpicture}
\end{document}