Letters can have up to 30 references in the main text; additional references can be cited in (and listed after) the Methods section, as detailed above. Each reference should have its own number, and you should please include final page numbers, as well as initial ones, unless the first ‘page’ is an article number (i.e. A&A beginning in 2010, ApJ beginning in 2011). Our abbreviations for the common astronomy journals are: Astrophys. J., Astron. J., Astron. Astrophys., Mon. Not. R. Astron. Soc.. Authors' last names should come first, followed by their initials. Any reference to work in preparation should be made in the main text, and not numbered in the reference list. As we are now printing the titles of all references cited, we would appreciate it if you could include them in the revised version of your text. The year of publication should be in parentheses at the end of the line.