By default, when using citep with natbib, the output is something like (Author et al., 1999), where there is a comma after the author, before the date. This is not the same format like that of ApJ, where the extra comma is not included. Using aastex or emulateapj should usually take care of this, but if you need to use natbib alone, it is possible to change the format using the ”aysep={char}” option in ”setcitestyle”:
setcitestyle{aysep={}}More info about this method here: gking.harvard.edu/files/natnotes2.pdf
More generally, you can use ”bibpunct” to change more of the punctuations. This command requires specification of six different components:
- the opening bracket symbol, default = (
- the closing bracket symbol, default = )
- the punctuation between multiple citations, default = ;
- the letter `n’ for numerical style, or `s’ for numerical superscript style, any other letter for author-year, default = author-year;
- the punctuation that comes between the author names and the year
- the punctuation that comes between years or numbers when common author lists are suppressed (default = ,);
The optional argument is the character preceding a post-note, default is a comma plus space. In redefining this character, one must include a space if one is wanted.
Example 1, bibpunct{[}{]}{,}{a}{}{;} changes the output of
citepjon90,jon91,jam92
into [Jones et al. 1990; 1991, James et al. 1992].
Example 2, bibpunct[; ]{(}{)}{,}{a}{}{;} changes the output of
citep[and references therein]{jon90}
into (Jones et al. 1990; and references therein).
See http://merkel.zoneo.net/Latex/natbib.php for more info.