Have questions not answered here? CONTACT US: j.eldridge [at] auckland.ac.nz and e.r.stanway [at] warwick.ac.uk 

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 five 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, I use only theoretical model spectra in my syntheses with as few empirical inputs as possible to create completely synthetic models to compare with observations. Fourthly, I use Cloudy (Ferland et al., 1998) to determine the nebular emission. This means I model not only the stars in detail but also the surrounding gas. 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. Select the data you require from the menu on the left. If you require data that is not here please email us.

The current version of the code is Version 2.1. It is discussed in detail in:

Version 2.0: this was the first release with many improvements to BPASS, it is discussed in:

Version 1.1: 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: this was the first version of the code. The models and synthesis code are outlined in the following papers:


BPASS results: outlining the predictions from BPASS and the importance of interacting binaries on stellar populations are outlined in:

Version 2:

Version 1:

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 can be found at:

Current members of the BPASS team:

  • JJ Eldridge: j.eldridge [at] auckland.ac.nz
  • Elizabeth Stanway: e.r.stanway [at] warwick.ac.uk.
  • Lin Xiao
  • Liam McClelland
  • John Bray

BPASS collaborators:

  • Stephanie Greis
  • Aida Wofford
  • Monica Relaño
  • Joe Walmswell
  • Maciej Hermanowicz

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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