I want to use the aastex style for an overleaf document, but I need to change the bibliography style, such that the references are indicated in the text as this is the references [1] and in the bibliography can mantain the standard \bibliographystyle{aasjournal}. I have read that I can get something similar by using \usepackage[square,numbers]{natbib}.

However, if I simply try to compile


it returns a conflict error:

 LaTeX Error: Option clash for package natbib.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.


The package natbib has already been loaded with options:
There has now been an attempt to load it with options
Adding the global options:
to your \documentclass declaration may fix this.
Try typing  <return>  to proceed.

Now, if I go to the aastex63.cls document, I only find two entries related to natbib and this problem:

% Restore natbib package without sorting. 

% only redefine sort@cites for natbib versions < 2009

I thought it was enough to comment out the first two of these lines, but this is evidently wrong. Any advice?

  • Hi, I work for the AAS Journals. This might be better handled on github.com/AASJournals/AASTeX60, but why do you need AASTeX and numbered rather than Author (Year) citations? This isn't a supported use case.
    – Gus
    May 1, 2020 at 19:01
  • @Gus, thank you. Dual-anonymous asks for that. I do not have a github account. Can I still post there?
    – Py-ser
    May 1, 2020 at 19:11
  • Do you mean dual-anonymous for PSJ? I am unaware of that requirement! Can you provide a link? And yes, you would need a github account to post there. This is fine though. If there's a deep issue we can't fix then I'll post an issue so we can keep track of it.
    – Gus
    May 1, 2020 at 19:42
  • It is a proposal that requires dual-anonymous. Not a journal publication.
    – Py-ser
    May 1, 2020 at 19:46
  • Ah, thank you. Again, I'm not sure that this is a supported use case (numbered references) since we have formally adopted Author (Year) style. If there is a proposal system that is requiring you to use AASTeX6+ and aasjournal.bst then please let me know. I think that the deeper problem is that AASTeX wraps revtex, which prevents passing natbib options all the way into it. But honestly I'm stumped.
    – Gus
    May 1, 2020 at 20:20

1 Answer 1


Try this:



\renewcommand\bibnumfmt[1]{[#1] }

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .