Astronomy Astrophysics Formatting Requirements: A&A Guide

A&A has specific abstract formatting rules that differ from most journals.

• Word limit: 300 words; the aa.cls class shows an error message for an abstract over 300 words

• Structure: Structured abstracts are encouraged but not mandatory

• Mandatory paragraphs if you use a structured abstract: Aims, Methods, and Results (Context and Conclusions are optional)

A&A encourages a structured abstract, which uses headings that define several short paragraphs. If you use one, Aims, Methods and Results are mandatory, and you may add an introductory Context paragraph and a final Conclusions paragraph. Authors who prefer the traditional form are asked to follow the same logical structure implicitly. The abstract should be self-contained: no references, and abbreviations or acronyms should be introduced. The elements, in order:

1. Context: Background and motivation (optional heading)

1. Aims: What the paper sets out to do (mandatory heading)

1. Methods: How it was done (mandatory heading)

1. Results: What was found, with quantitative data (mandatory heading)

1. Conclusions: What it means (optional heading)

The structured abstract is an encouraged convention rather than a requirement, so a traditional abstract that follows the same logic is acceptable.

A&A has detailed figure requirements. Figures are a major component of most astronomy papers.

Figure formatting requirements:

Color: The guide does not allow background grids and colors in figures unless they contain additional information, and it asks authors to avoid combining red and green because color-blind readers cannot distinguish them. It also asks authors to check whether laser-printed originals of figures are acceptable, especially for grayscale. Use distinct line styles (solid, dashed, dotted) in addition to colors, and avoid relying on color alone to distinguish data series.

Astronomical imaging conventions: Sky images should follow the IAU convention (north up, east left). Coordinate axes should use standard astronomical notation (Right Ascension in hours/minutes/seconds, Declination in degrees/arcminutes/arcseconds). Spectral plots should clearly label wavelength or frequency units.

Table formatting: A&A uses its own table formatting through LaTeX. Use the table environment. Every column, including the first, needs a heading. Units go in parentheses immediately below the column headings, the caption goes above the table, and a table including its caption usually must not exceed 23.5 cm in height. For large tables of primary data, A&A archives the data at the CDS (the Strasbourg astronomical data center, which hosts VizieR).

A&A uses a distinctive author-year citation style that differs from both the AAS (ApJ) system and the standard astronomy citation formats.

In-text citations:

• Single author: Author (Year) or (Author Year)

• Two authors: Author1 & Author2 (Year) or (Author1 & Author2 Year)

• Three or more: Author1 et al. (Year) or (Author1 et al. Year)

Reference list format:

The reference list is alphabetical by first author's last name.

Author, A. B., Author, C. D., & Author, E. F. Year, Journal Abbreviation, Volume, Page

Key formatting details:

• Author names: Last name, initials (with periods)

• Ampersand before last author

• Year follows author list

• Journal abbreviation follows A&A conventions (A&A, ApJ, MNRAS, etc.)

• Volume number follows journal abbreviation

• Article or page number (e.g., A23 for A&A articles)

• No title in the reference (this is a key difference from many journals)

Worked example:

Zhang, Y., Chen, L., & Patel, W. R. 2026, A&A, 689, A145

Note: no article title. A&A references for journal articles don't include the article title. This is one of the most distinctive features of the A&A reference format. Book references do include titles, but journal articles do not. This catches authors coming from journals that require titles in all references.

The natbib package, used with aa.cls, handles the citation formatting automatically. Use \citet{} for textual citations and \citep{} for parenthetical citations.

A&A requires manuscripts to be formatted in LaTeX2e using the current A&A macro package, which includes the aa.cls document class. There is no Word option.

LaTeX setup:

• Document class: \documentclass{aa} (using the aa.cls file)

• Download the latest A&A macro package, including aa.cls, from the A&A LaTeX instructions

• The package includes aa.cls, aa.bst (bibliography style), and a template file

• Use natbib for citations: \usepackage{natbib}

• Use standard astronomy packages: astropy, aastex_hack isn't needed since you're using aa.cls

Key aa.cls features:

• Handles the two-column layout automatically

• Provides \abstract{} with Context, Aims, Methods, Results, Conclusions support

• Includes \keywords{} for keyword specification

• Provides \corrauth and \email for author e-mail addresses (class update, March 2026)

Essential tip: Don't modify the aa.cls file. The guide warns that using aa.cls with other versions or implementations may cause difficulties, and it asks authors not to use self-made definitions because they get lost during conversion. If you need custom formatting, use standard LaTeX commands within the aa.cls framework.

No article titles in references. This is the single most common formatting error from first-time A&A authors. Journal article references in the A&A style do not include the article title. Only book references, proceedings, and theses include titles. The aa.bst bibliography style handles this automatically if your.bib file is properly formatted.

Page charges for long papers. Pages above the caps (12 main-body pages and 8 appendix pages for a regular paper) incur page charges of EUR 150 to 200 per page, and first authors from non-sponsoring countries also pay per page within the cap. Plan your paper length accordingly. Large tables of primary data can be archived at the CDS.

Appendices are camera-ready. From July 2021, A&A does not typeset appendix pages and includes them at the end of the article as camera-ready material. No correction, copyediting or layout change is made after the publisher receives the accepted version, so prepare appendices carefully.

Keywords from a controlled list. A&A allows a maximum of 6 key words, selected from a list common to the major astronomical and astrophysical journals. You can't use free-form keywords. Check the list on the A&A website before selecting your keywords.

Astronomical object names. A&A links the most important objects in an article to the Simbad or NED databases with the \object{} directive. The guide says the number of such links should not exceed some 10-20 occurrences and that the directive should be avoided in tabular material, so tag only the objects the article studies.

CDS data deposit. A&A makes it mandatory to publish the data presented and discussed in an article and needed to reproduce the results, usually at the Centre de Donnees astronomiques de Strasbourg (CDS), immediately upon acceptance. The CDS requires data tables in ASCII format with a ReadMe file, and primary data can also be archived as FITS files. If the primary observational data are already archived at a public facility such as ESO or HST, only the reduced data are archived.

Language editing. A&A sends papers to language editors after acceptance, at the recommendation of the referee or one of the editors, and not all papers are looked at by a language editor. The guide holds the authors responsible for a correct formulation of their text.

Section numbering. A&A uses numbered sections. The standard structure is: 1. Introduction, 2. Observations/Methods, 3. Results, 4. Discussion, 5. Conclusions. Follow the numbering convention.

A standard A&A Regular Article follows this structure:

The structure is flexible within this framework. Observational papers might combine Observations and Results. Theoretical papers might have a Theory section. Instrumentation papers will have their own appropriate structure.

For manuscripts targeting Astronomy & Astrophysics, four patterns generate the most consistent desk-rejection outcomes.

A&A LaTeX class (aa.cls) not used. The journal requires the aa.cls macro package, available from the A&A website. Papers formatted in AASTeX (the ApJ/AJ standard) or with a generic LaTeX article class are returned before peer review. The confusion between aa.cls and aastex is the single most common administrative return at A&A: the two packages produce visually similar output, but reviewers and editors can identify the wrong class file from the typesetting conventions and header format.

Observational data not deposited or referenced in CDS/VizieR. A&A makes it mandatory to publish the data needed to reproduce the results, usually at the Strasbourg CDS, and the text should refer to the material published electronically. Papers reporting astrometric catalogues, photometric survey data, or spectral line lists without CDS submission are asked to complete the deposit upon acceptance.

Incremental result submitted as a Regular Article. A&A discontinued its Research Notes category in 2016, so a single novel result or incremental follow-up has no short category of its own. Incremental or confirmatory results submitted as Regular Articles are flagged at editorial triage; the editor will typically reject for scope.

Statistical reporting inconsistent with astronomical community standards. A&A applies community norms for uncertainty reporting: symmetric and asymmetric error bars, upper limit conventions, Bayesian credible intervals vs. frequentist confidence intervals, and completeness corrections for survey-based results. Papers reporting detection significance without false-alarm probability analysis, or photometric fits without explicit uncertainty propagation, are sent back for methodological revision before the science is assessed, and in our review work this is the failure that most often survives an otherwise clean aa.cls compile.

A Astronomy & Astrophysics submission readiness check evaluates manuscript structure, LaTeX template compliance, and data availability against these desk-rejection patterns before submission.