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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 2.3. (Released March 2022)

This is a limited release of spectral synthesis products only, exploring the effects of varying the stellar atmosphere compositions, used together with the v2.2 population synthesis models. The v2.3 release is accompanied by a release paper: Byrne et al (2022). It builds on the more detailed descriptions of the physics in Stanway & Eldridge (2018),  and Eldridge, Stanway et al (2017, PASA)arXiv:1710.02154

The variant spectral synthesis libraries discussed in Byrne et al 2023 can be found at BPASS v2.3.1 release.

The stochastic sampling data discussed in Stanway & Eldridge 2023 and based on BPASS v2.2.1 can be found at BPASS_v2.2_stochastic

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 2.2.1 (Current results for popsynth and data products)

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:


Principle Investigators of the BPASS project:

  • JJ Eldridge: j.eldridge [at] 
  • Elizabeth Stanway: e.r.stanway [at]

Past and present postdoctoral researchers on the BPASS team:

  • Heloise Stevance (Postdoctoral Researcher)
  • Conor Byrne (Postdoctoral Researcher)

Past and present postgraduate students working on the BPASS team:

  • Ashley Chrimes (now postdoctoral researcher)
  • Gareth Jones (PhD candidate)
  • Sohan Ghodla (PhD candidate)
  • Max Briel (PhD candidate)
  • Wouter van Zeist (PhD candidate)
  • Petra Tang (PhD candidate)
  • John Bray (now postdoctoral researcher)
  • Lin Xiao (now postdoctoral researcher)
  • Liam McClelland (left astronomy)
  • Steph Greis (left astronomy)

The creation of BPASS has been supported by:

  • Royal Society te Aparangi, New Zealand.
  • Science and Technology Facilities Council, United Kingdom.
  • Department of Physics, University of Auckland, New Zealand.
  • Department of Physics, University of Warwick, United Kingdom.
  • 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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