Clash between siunitx and AASTeX

Question

I am encoutering an issue when trying to use the table formatting provided by siunitx in a AASTeX document.

\documentclass{aastex631}
\let\tablenum\relax
\usepackage{siunitx}

\begin{document} 
    
\begin{tabular}{S[table-format = 1.2e2]|S[table-format = 1.2e2]}
 1.23e45 & 6.78e9 \\
\end{tabular}

\end{document}

(the \let\tablenum\relax is already here to solve some conflicts between the two, as described in AASTeX Author Guide

I am simply trying to define two columns with siunitx formatting and I get the following error:

Misplaced alignment tab character &.
You have placed an alignment tab character '&' in the wrong place. If you want to align something, you must write it inside an align environment such as \begin{align} … \end{align}, \begin{tabular} … \end{tabular}, etc. If you want to write an ampersand '&' in text, you must write \& instead.

If I replace aastex631 by article in the first line or if I only define one S column, the issue disappears. But in my real case, I need to use aastex631 AND to define at least three S columns.

Do you know where the issue could come from, and how I could solve it?

Thanks in advance!

Answer 1

The class makes the & active and disturbs the parsing of siunitx. It seems to work if you add a \relax

\documentclass{aastex631}
\let\tablenum\relax
\usepackage{siunitx}
\begin{document}

\begin{tabular}{S[table-format = 1.2e2]|S[table-format = 1.2e2]}
 1.23e45 \relax & 6.78e9 \\
\end{tabular}

\end{document}