Space underneath double horizontal lines in deluxetable

[dsvinkin]

Hi All,

I have discovered the following issue (aastex 6.3 and 6.3.1). In case of
\documentclass[manuscript]{aastex631}
the modification of the table text size with \tabletypesize, e.g.
...
\begin{deluxetable*}{cchlDlc}
\tabletypesize{\scriptsize}
\tablenum{1}
\tablecaption{Fun facts about the first 10 messier objects\label{tab:messier}}
...
gives the following result (produced using sample631.tex from aastex 6.3.1 distribution from https://journals.aas.org/aastex-package-for-manuscript-preparation/):

As we (@mulanov and me) found that this issue is due to reduction of the vertical skip
\hline\hline\noalign{\vskip-9pt}%
at line 4913 of aastex631.cls (after \def\zdeluxetable)
Removing \noalign{\vskip-9pt} makes table look normal.

The comment at the end of cls file:

14. \tablehead in deluxetable had too much space underneath
    double horizontal lines. Made custom negative skip based
    on each style, tested, and supplied tabsamples.zip showing
    tableheads in each style.

mentions "custom negative skip", but the skip seems to be fixed (not custom).