Astronomy Astrophysics Formatting Requirements: A&A Guide

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

• Word limit: Approximately 250 words for Regular Articles, 100 words for Letters and Research Notes
• Structure: Semi-structured with specific elements
• Required elements: Context, Aims, Methods, Results, and Conclusions

The A&A abstract uses an informal structured format. While it doesn't use bold subheadings like a medical journal, the abstract should address these elements in order:

1. Context: Background and motivation (1-2 sentences)
2. Aims: What the paper sets out to do (1 sentence)
3. Methods: How it was done (1-2 sentences)
4. Results: What was found, with quantitative data (2-3 sentences)
5. Conclusions: What it means (1 sentence)

This semi-structured format is unique to A&A and isn't used by ApJ or MNRAS. Follow the convention. Reviewers and editors notice when the abstract doesn't address all five elements.

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

Figure formatting requirements:

Color figures: Color is free for the online version of the paper. However, the print edition uses grayscale. This means all figures must be legible in grayscale. Use distinct line styles (solid, dashed, dotted) in addition to colors, and avoid relying on color alone to distinguish data series. You'll need to provide both color and grayscale versions if the color version isn't readable in black and white.

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 or table* environment. Every column needs a header. Units go in the header row (in parentheses or using appropriate notation). Footnotes below using superscript lowercase letters. For large data tables, A&A encourages the use of VizieR (the CDS astronomical catalog service) to host the data.

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)

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 the use of its own LaTeX document class, aa.cls. While Word submissions are theoretically accepted, the journal's workflow is built entirely around LaTeX.

LaTeX setup:

• Document class: \documentclass{aa} (using the aa.cls file)
• Download aa.cls from the A&A author page
• 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
• Supports \onlineonlytable for tables published only online
• Handles the \thanksref system for affiliations

Essential tip: Don't modify the aa.cls file. The production team uses the standard version, and modifications can cause compilation errors. If you need custom formatting, use standard LaTeX commands within the aa.cls framework.

1. 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.

2. Page charges for long papers. Papers exceeding 16 printed pages incur mandatory page charges. The rate is set by the journal and isn't trivial. Plan your paper length accordingly. Move large tables and supplementary data to online-only appendices or VizieR.

3. Online-only tables and figures. A&A supports online-only material that appears in the electronic version but not the print edition. Use \onlineonlytable and \onlineonlyfigure environments. Large catalogs, extensive data tables, and supplementary figures should use this feature rather than being submitted as separate supplementary files.

4. Keywords from a controlled list. A&A requires keywords selected from the journal's standardized keyword list. You can't use free-form keywords. The list covers astronomical objects, techniques, physical processes, and survey categories. Check the list on the A&A website before selecting your keywords.

5. Astronomical object names. Use SIMBAD-compatible object names. When first mentioning an astronomical object, include its standard identifier. A&A links object names to the SIMBAD database, so using non-standard names breaks the linking system.

6. CDS data deposit. A&A encourages (and for large catalogs, requires) data deposit with the Centre de Donnees astronomiques de Strasbourg (CDS). Tables available through VizieR should be formatted using the CDS standard and referenced in the paper.

7. Language editor availability. A&A provides language editing for non-native English speakers. The service is free and is offered during the editorial process. This is unusual for a major journal and is worth knowing about.

8. 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:

1. Title (descriptive, specific to the astronomical topic)
2. Author names and affiliations (using the aa.cls affiliation system)
3. Abstract (semi-structured: Context, Aims, Methods, Results, Conclusions)
4. Keywords (from the A&A controlled keyword list)
5. 1. Introduction
6. 2. Observations and Data Reduction (or Methods/Theory)
7. 3. Results
8. 4. Discussion
9. 5. Conclusions
10. Acknowledgements
11. References (alphabetical, no article titles)
12. Appendices (optional)
13. Online-only material (if applicable)

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.

These cause the most delays at A&A:

• Including article titles in journal references (A&A style omits them)
• Not using the aa.cls document class
• Using free-form keywords instead of the A&A controlled list
• Exceeding 16 pages without budgeting for page charges
• Color figures that aren't legible in grayscale
• Non-standard astronomical object names that don't link to SIMBAD
• Using AAS or MNRAS citation format instead of A&A style
• Missing the semi-structured abstract format (Context, Aims, Methods, Results, Conclusions)
• Figures in wrong format (A&A prefers EPS/PDF, not TIFF)

For more on this journal, see our Astronomy & Astrophysics submission guide, Astronomy & Astrophysics submission process, and Astronomy & Astrophysics cover letter guide.

For the official author guidelines and the aa.cls download, visit the A&A information for authors.

Treat A&A formatting as part of the scientific package. The aa.cls file, structured abstract, reference style, controlled keywords, figure formats, and page-length economics all tell editors whether the manuscript was prepared for this journal rather than transferred from ApJ, MNRAS, or a generic astronomy template.

In our pre-submission review work with 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 requires that tables of observational data accompanying a paper be submitted to the Strasbourg CDS for hosting in VizieR, with the accession reference included in the manuscript. Papers reporting astrometric catalogues, photometric survey data, or spectral line lists without CDS submission face delays at the proof stage and requests to complete the deposit before publication.

Research Note scope submitted as a Regular Article. A&A distinguishes Research Notes (single novel result or incremental follow-up, maximum 4 published pages) from Regular Articles (full investigation). Incremental or confirmatory results submitted as Regular Articles are flagged at editorial triage; the editor will typically ask for reclassification or 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.

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