كيف  أمنع ظهور الخط الأسود على وثيقة ببرنامج LaTeX؟

جرب الكود التالي، والذي حاولت من خلاله منع ظهور الخط العريض بجانب الرسم:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{verbatim}
\usepackage{tikz}
\usepackage{amsmath}
\usepackage[margin=3cm]{geometry}
\usepackage{mathtools}
\usepackage{graphicx}
%\usepackage[]{mcode}
\usepackage[swedish]{babel}
\usetikzlibrary{calc}
\usepackage{float}
\usepackage{subfig}

\parindent=0pt
\setlength{\parskip}{1em}

\title{Matematisk modellering}
\author{}
\date{February 2016}
\begin{document}

\begin{figure*}[t!]\centering
\begin{tikzpicture}
[
scale=3,
>=stealth,
point/.style = {draw, circle,  fill = black, inner sep = 1pt},
dot/.style   = {draw, circle,  fill = black, inner sep = .2pt},
]
%
% the circle
\draw (0,0) circle (2.12cm);
%
% triangle nodes: just points on the circle
\node (n0) at (0,0) [point, label = below:$S$] {};
\node (n1) at (-1.5,1.5) [point, label = below:$R_{1}$] {};
\node (n2) at (-3,0) [point, label = {below left:$R_{2}$}] {};
\node (n3) at (-2.12,0) [point, label = {below left:$q$}] {};
%
% triangle edges: connect the vertices, and leave a node at the midpoint
\draw[-] (n0) -- node (a) [label = {below left:$\gamma$}] {} (n1);
\draw[-] (n0) -- node (a) [label = {below right:$\gamma$}] {} (n2);
\draw[-] (n2) -- node (a) [label = {below :$vt_{1,2}$}] {} (n3);
\end{tikzpicture}

\end{figure*}

\end{document}

وهذه هي نتيجة ما حصلت عليه: