citation-style-language/styles — pull request #554 by indiajoe (2013-05-15 08:54:32+00:00)
Title: Changed et-al-use-first="3"

For ApJ journal, If there are more than 5 authors, then "et al." should be added after first three authors name.
See http://aas.org/authors/manuscript-preparation-aj-apj-author-instructions#references