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Binary Population And Spectral Synthesis (BPASS)

Note that this page mirrors content on the BPASS page at This mirror is maintained by Elizabeth Stanway.

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 detailed binary 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, 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, we use only theoretical model spectra i with as few empirical inputs as possible to create completely synthetic models to compare with observations. Fourthly, we encourage use of Cloudy (Ferland et al., 1998) to determine the nebular emission. Finally, the code is easily adaptable to determine the input physical parameters required to match observations.

On this site we make available standard outputs from our code for single and binary star populations. If you require data that is not here please email us with your request or suggestion.

The current version of the code is Version 2.3. (Released March 2022)

The v2.3 release is accompanied by a paper: Byrne et al (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. It builds on the more detailed descriptions of the physics in Stanway & Eldridge (2018), and Eldridge, Stanway et al (2017, PASA), arXiv:1710.02154. BPASS v2.2 remains the preferred data release for population synthesis data products.

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

The Python package HOKI is designed to make reading and manipulating BPASS output files more straightforward for Python users, and includes a number of tutorials which are recommended for new users. It is described in Stevance et al (2020).

June 2021: Due to frequent requests, we make available a set of cloudy-processed BPASS v2.2.1 files including nebular emissionLink opens in a new window, but caution that users should ensure they understand the radiative transfer prescription in Cloudy and ensure that the input parameters are appropriate for their science.

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

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.


This site also hosts other results from the Auckland Stars Group that are not included in BPASS. These can be found under the Other Results page. To date these numbers are based on the following paper:


BPASS image