Adapting my answer to Is it possible to have a two-column figure caption in revtex?
\documentclass{aastex}
%\usepackage{spr-astr-addons} % I haven't it
\usepackage{url}\urlstyle{rm}
\usepackage{graphicx}
\usepackage{color}
\usepackage[caption=false]{subfig}
\usepackage{lipsum}
\captionsetup[subfigure]{position=top}
\makeatletter
\newcommand{\twocolumncaption}{\@dblarg\@twocolumncaption}
\def\@twocolumncaption[#1]#2{%
\renewcommand{\@makecaption}[2]{%
\par\vskip\abovecaptionskip\begingroup\small\rmfamily
\splittopskip=0pt
\setbox\@tempboxa=\vbox{
\@arrayparboxrestore \let \\\@normalcr
\hsize=.5\hsize \advance\hsize-1em
\let\\\heading@cr
\noindent ##1\ ##2\par% this line for aastex
}%
\vbadness=10000
\setbox\z@=\vsplit\@tempboxa to .55\ht\@tempboxa
\setbox\z@=\vtop{\hrule height 0pt \unvbox\z@}
\setbox\tw@=\vtop{\hrule height 0pt \unvbox\@tempboxa}
\noindent\box\z@\hfill\box\tw@\par
\endgroup\vskip \belowcaptionskip
}%
\setlength{\abovecaptionskip}{4ex}%
\caption[#1]{#2}%
}
\makeatother
\begin{document}
\title{Title}
\author{A. Uthor}
\affil{Somewhere}
\begin{abstract}
\lipsum[2]
\begin{description}
\item[PACS numbers] 04.50.Kd, 04.20.-q, 04.25.Nx
\end{description}
\end{abstract}
\keywords{Keywords}
\maketitle
\section{Intro}
\lipsum[1-3]
\begin{figure*}
\centering
\subfloat[]{\includegraphics[width=0.25\textwidth]{example-image}}\
\subfloat[]{\includegraphics[width=0.25\textwidth]{example-image}}\
\subfloat[]{\includegraphics[width=0.25\textwidth]{example-image}}\
\subfloat[]{\includegraphics[width=0.25\textwidth]{example-image}}\
\subfloat[]{\includegraphics[width=0.25\textwidth]{example-image}}\
\subfloat[]{\includegraphics[width=0.25\textwidth]{example-image}}\
\subfloat[]{\includegraphics[width=0.25\textwidth]{example-image}}\
\subfloat[]{\includegraphics[width=0.25\textwidth]{example-image}}\
\subfloat[]{\includegraphics[width=0.25\textwidth]{example-image}}
\twocolumncaption{%
Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Ut purus elit, vestibulum ut,
placerat ac, adipiscing vitae, felis. Curabitur dictum gravida mauris. Nam arcu libero,
nonummy eget, consectetuer id, vulputate a, magna. Donec vehicula augue eu neque.
Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis
egestas. Mauris ut leo. Cras viverra metus rhoncus sem. Nulla et lectus vestibulum
urna fringilla.}
\end{figure*}
\lipsum
\section{Conclusion}
\lipsum
\end{document}

If the Springer style already makes the two column caption, remove the code from \makeatletter
to \makeatother
(included) and just use \caption
.
aastex
document class you use. (It doesn't appear to be the latest version, i.e., version 6.1, as that document class isn't compatible with some of the other LaTeX packages you load.) – Mico Oct 21 '16 at 13:07aastex
. I am new to latex. Is there a way to check it? – MrDi Oct 21 '16 at 13:15