BPASS v2.3

Latest BPASS version 2.3 Data Release (March 2022)

This version of BPASS represents a limited data release, which extends our BPASS v2.2 model grid. The version 2.3 models are identical in input physics to the version 2.2 release, except that they substitute the newer C3K stellar atmosphere models of main sequence and giant stars for the older CKC14 atmosphere model grid. This permits elemental abundance ratios to be modified.

They are presented for a single IMF (imf135_300). However at each metallicity, we now produce five possible spectral energy distributions constructed with stellar atmosphere models with different elemental compositions. The stellar atmospheres were constructed with the Asplund et al (2009) Solar chemical composition. The filename suffixes [a-02, a+00, a+02, a+04, a+06] refer respectively to stellar models with the same total metal fraction by mass (Z, with Zsun=0.020), but in which the fraction of mass in alpha elements relative to Iron has been modified by Δ(log(alpha/Fe)) = -0.2, +0.0, +0.2, +0.4 and +0.6.

To maintain the same total metallicity, this implies that Fe/H must also vary (i.e. spectra which are alpha-rich compared to Solar composition are also Iron poor). We note that the v2.2.1 models (which used an older Solar abundance pattern) had a slightly higher alpha to iron ratio than the base abundance pattern used here.

BPASS v2.3 is described in Byrne et al (2022, MNRAS in press). Its underlying physics is described in the v2.2 paper Stanway & Eldridge (2018, MNRAS). This, in turn, builds on the much longer and more detailed v2.1 release paper Eldridge, Stanway et al, 2017, PASA .

We have also produced an updated User Manual which we strongly recommend users examine, which provides file name explanations and readmes for the output. This is available as a PDF typeset in both Arial and OpenDyslexic3 (a font designed for use by those with specific learning differences).

The v2.3 data release is stored on OneDrive at BPASS_v2.3_release.

The limited v2.3 release contains spectral synthesis data products as follows (all versus age, for 1 IMF, 13 metallicities, 5 abundance grids):

• Spectral Energy Distributions
• Ionizing flux predictions
• Broadband colours
• Lick Indices
• UV line indices

For full details, and README details for the data files, we again recommend the User Manual. The file format has not changed and files remain compatible with the Hoki python package.

We would appreciate the inclusion of the following acknowledgement where appropriate:

“This work made use of v2.3 of the Binary Population and Spectral Synthesis (BPASS) models as described in Byrne et al (2022) and Stanway & Eldridge (2018).”

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

Note:

The slightly older v2.2.1 models are still online at this link and are still the primary release for all population synthesis and stellar model outputs.