The central star of the Ring Nebula is discovered by Fredrich von Hahn: the central star is a white dwarf star with a temperature of between 100000 and 120000 K.
^Elaut, L. (July 1969). "The theory of membranes of F. X. Bichat and his predecessors". Sudhoffs Archiv (West Germany) 53 (1): 68–76. ISSN0039-4564. PMID4241888.