Dot with only operator overline

Question

I have read this question Special character "dot over dash" for solved my problem. But my question is little different and it is not duplicate.

How to have using command \overline a \dot (or more greater than \dot in the middle and is it almost near the vector mark \overline? I bring back what I would like with a picture:

I made a very impromptu attempt.

\documentclass[a4paper,12pt]{article}
\usepackage{mathtools}
\begin{document}
\[\dot{\hspace{-.072cm}\overline J}=\frac{\partial \overline J}{\partial \tau}\]
\end{document}

Answer 1

Honestly I'm not sure it's worth the effort (I use \overline as rarely as possible). My phantasy wasn't rich enough to come up with a name...

\documentclass{article}

\def\foo{\mathpalette\fooaux}
\def\fooaux#1#2{%
  \mkern2mu
  \setbox0=\hbox{\mathsurround=0pt$#1\overline{\mkern-2mu #2 \mkern2mu}$}%
  \setbox1=\hbox to \wd0{\hss$#1\cdot$\hss}%
  \vbox{\offinterlineskip\copy1\vskip-.4\ht1\box0}%
  \mkern-2mu
}

\begin{document}

$\dot{\overline{J}} J \overline{J} J \foo{J}J$

$\scriptstyle \dot{\overline{J}} J \overline{J} J\ foo{J}J$

$\scriptscriptstyle \dot{\overline{J}} J \overline{J} J \foo{J}J$

\end{document}

Answer 2

\documentclass{article}
\usepackage{stackengine,amsmath,graphicx}
\stackMath
\newcommand\overlinedot[1]{%
  \stackengine{.2pt}{\overline{#1}}{\scalebox{2}{.}}{O}{c}{F}{F}{S}%
}
\begin{document}
\[
\overlinedot{J}=\overlinedot{x}
\]
\end{document}

A version that works across math styles.

\documentclass{article}
\usepackage{stackengine,amsmath,graphicx,scalerel}
\newcommand\overlinedot[1]{\ThisStyle{\ensurestackMath{\stackengine%
  {.2\LMpt}{\SavedStyle\overline{#1}}{\scalebox{2}{$\SavedStyle.$}}{O}{c}{F}{F}{S}%
}}}
\begin{document}
\[
\overlinedot{J}=\overlinedot{x}
\]
\[
\scriptstyle\overlinedot{J}=\overlinedot{x}
\]
\[
\scriptscriptstyle\overlinedot{J}=\overlinedot{x}
\]
\end{document}

Answer 3

\documentclass[a4paper,12pt]{article}
\usepackage{mathtools}

\usepackage{mattens}
\SetSymbFont{\relax}

\begin{document}

\[\bS[\dot]{J}=\frac{\partial \overline J}{\partial \tau}\]

\end{document}