I'm working with the natbib package and the aa bibliography style for the Astronomy & Astrophysics journal. One author wrote two papers in the same year. The problem is with how the references and citations are sorted. schoier 2006b is being displayed as schoier 2006a.

My bibliographic entry:

   author = {{Sch{\"o}ier}, F.~L. and {Olofsson}, H. and {Lundgren}, A.~A.
    title = "{SiO in C-rich circumstellar envelopes of AGB stars: effects of non-LTE chemistry and grain adsorption}",
  journal = {\aap},
 keywords = {stars: AGB and post-AGB, stars: carbon, stars: circumstellar matter, stars: late-type, stars: mass-loss},
     year = 2006,
    month = jul,
   volume = 454,
    pages = {247-255},
      doi = {10.1051/0004-6361:20054795},
   adsurl = {http://adsabs.harvard.edu/abs/2006A%26A...454..247S},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}

   author = {{Sch{\"o}ier}, F.~L. and {Fong}, D. and {Olofsson}, H. and {Zhang}, Q. and 
    {Patel}, N.},
    title = "{The Distribution of SiO in the Circumstellar Envelope around IRC +10216}",
  journal = {\apj},
 keywords = {Stars: Circumstellar Matter, Stars: Abundances, Stars: AGB and Post-AGB, Stars: Carbon, Stars: Individual: Alphanumeric: IRC +10216, Stars: Mass Loss},
     year = 2006,
    month = oct,
   volume = 649,
    pages = {965-972},
      doi = {10.1086/506199},
   adsurl = {http://adsabs.harvard.edu/abs/2006ApJ...649..965S},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}

My code:




In the output bibliography, the references a and b are wrongly associated:

Schöier, F. L., Fong, D., Olofsson, H., Zhang, Q., & Patel, N. 2006a, ApJ, 649,965
Schöier, F. L., Olofsson, H., & Lundgren, A. A. 2006b, A&A, 454, 247

This happens as well in the text.

  • 3
    The entry keys in your database the (sch2006a and sch2006b) usually have no bearing on the sorting and ultimately the disambiguation letter added after the year. In this case you get the result because the name list of the Schöier, F. L., Fong, D., sorts before Schöier, F. L., Olofsson, H. (F<O). If you wanted a different sort order you would have to tweak stuff manually or tell your style to also take the month into account (jul<oct)
    – moewe
    Mar 1, 2019 at 13:00
  • 1
    Given that you are using a publisher class I would not bother modifying the style: The output is (hopefully) as desired by the publisher (and if not, that would be a bug to report to the maintainer).
    – moewe
    Mar 1, 2019 at 13:07

1 Answer 1


The aa bibliography style appears to sort entries alphabetically by the surnames of all authors, not just by the surname of the first author.

Both entries have the same first author ("Schöier"). However, the entry with key sch2006b has "Fong" as the second author. It is therefore correctly sorted before the sch2006a entry, whose second author is "Olofsson".

The fact that the key sch2006a precedes sch2006b alphabetically is of no consequence.

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