Sirius C is invisible to the photographic lens and the naked eye but this does not mean that it does not exist. Sirius B was known to the Dogon for over 4,000 years before its existence was proven.
Ironically, the name for Sirius C is the same name given to the location where Egyptian high culture emerged....ANU.
Sirius B itself is a star much younger in its development than our Sol. And Sirius is a binary system still in its infancy.
Personally, since the Dogon correctly have created a calendar system based on the Sothic cycle that is still in use among their society I shall accept their account until it is proven inaccurate.