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Have questions not answered here? CONTACT US: j.eldridge [at] and e.r.stanway [at] 

The Binary Population and Spectral Synthesis code (BPASS) is the result of combining my stellar evolution models with libraries of synthetic atmosphere spectra to create a unique tool to model many details of stellar populations. While similar codes (such as starburst99) exist BPASS has important features, each of which set it apart from other codes and in combination make it the cutting edge. First, and most important, is the inclusion of binary evolution in modelling the stellar populations. The general effect of binaries is to cause a population of stars to look bluer at an older age than predicted by single-star models. Secondly, detailed stellar evolution models are used rather than an approximate rapid population synthesis method. Thirdly, only theoretical model spectra are used in the syntheses with as few empirical inputs as possible to create completely synthetic models to compare with observations.  

On this site we make available standard outputs from our code for single and binary star populations. Select the data you require from the menu above. If you require data that is not here please email us.

The current version of the code is Version 2.2.1 (July 2018)

The v2.2 release (May 2018) was accompanied by a release paper: Stanway & Eldridge (2018), which builds on the more detailed model description in Eldridge, Stanway et al (2017, PASA)arXiv:1710.02154.  Subversion v2.2.1 fixes a slight mis-scaling of a small number of white dwarf atmospheres, which resulted in negative fluxes at a handful of ages and wavelengths. Changes to most observable parameters are very small. 

Python users are encouraged to download and use the BPASS Python package HOKI, prepared for the project by Heloise Stevance. HOKI is designed to make reading and manipulating BPASS files straightforward in the Python environment. The HOKI website also includes a number of recipes, tutorials and example applications.

License: The results from BPASS and CURVEPOPS available on this site licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Creative Commons License

Older releases:

Version 2.1 (deprecated)

Version 2.0 (deprecated)

this was the first release with many improvements to BPASS, it is discussed in:

Version 1.1 (deprecated): this was the version that first included stars that experience quasi-homogeneous evolution at the lowest metallicities of Z=0.001 and 0.004. The version and results are outlined in:

Version 1.0 (deprecated): this was the first version of the code. The models and synthesis code are outlined in the following papers:



Current members of the BPASS team:

  • JJ Eldridge: j.eldridge [at]
  • Elizabeth Stanway: e.r.stanway [at]
  • Heloise Stevance
  • Conor Byrne
  • Ashley Chrimes
  • Max Briel
  • Wouter van Zeist
  • Sohan Ghodla
  • Gareth Jones
  • Petra Tang

BPASS collaborators:

  • John Bray
  • Stephanie Greis
  • Aida Wofford
  • Monica Relaño
  • Joe Walmswell
  • Maciej Hermanowicz
  • Lin Xiao
  • Liam McLelland

The creation of BPASS has been supported by:





  • Department of Physics, University of Auckland, New Zealand.
  • Department of Physics, University of Warwick, United Kingom.
  • Astrophysics Research Centre, Department of Physics, Queen’s University Belfast, Northern Ireland.
  • Institute of Astronomy, University of Cambridge, United Kingdom.
  • Institut d’Astrophysique de Paris, University de Pierre & Marie Curie, France.


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