For users on Linux operating systems, one change in v6.1 will cause problems on compilation. A hidden ".bib" file is created in v6.1 but the default behavior LaTeX on Linux is to not allow any files to be written that begin with a period. This is not a problem on Windows or Mac operating systems. There are two work arounds available until this bug is fixed (Note that the first option has been implemented in any copy of aastex61.cls downloaded after Dec. 28th, 2016).
%% get rid of \jobname Notes being sent to .aux file:
openout_any=a pdflatex file