Our recently published stellar population models (Dahmer-Hahn et al. 2026). Built with the Maraston (1998, 2005) code, following the recipe of Maraston & Stromback (2011), and the BOSZ library of stars (Bohlin et al. 2017, Meszaros et al. 2024) as input. The latest version of the BOSZ library covers a wide range of stellar parameters, namely Teff between 2,800 and 16,000K, log(g) between -0.5 and 5.5, total metallicity [M/H] between -2.5 and +0.75, with wavelength coverage between 500 and 320,000A. This stellar parameter space allows the calculation of models older than ~0.1Gyr. The models, as of November/2026, come in for four combinations of [alpha/M] and [C/M]:

- [alpha/M]=+0.00, [C/M]=+0.00
- [alpha/M]=+0.00, [C/M]=+0.25
- [alpha/M]=+0.25, [C/M]=+0.25
- [alpha/M]=+0.25, [C/M]=+0.50

Each combination of [alpha/M] and [C/M] comes in four metallicities:

- [Fe/H]=+0.35
- [Fe/H]=+0.00
- [Fe/H]=-0.33
- [Fe/H]=-1.35

Three IMFs:

- IMF=+1.30, Kroupa
- IMF=+2.35, Salpeter
- IMF=+3.00, bottom-heavy

And ages between 0.1 and 15Gyr.

Naming convention is:

M26_BOSZ_feh*****_a*****_c*****_t*****_imf*****.spec

Where asterisks represent each respective parameter. So, for example:

M26_BOSZ_feh+0.00_a+0.00_c+0.00_t0.1E9_imf+3.00.spec

Represents a model with:

[Fe/H]=+0.00
[alpha/M]=+0.00
[C/M]=+0.00
Age=0.1Gyr
IMF=+3.00, i.e. bottom heavy

These models are the first in the literature to fully explain CO bands in the Near-Infrared. The following Figure shows how models with [alpha/M]=0 and [C/M]=0 are not deep enough to explain the CO absorptions in massive Early-Type galaxies (represented by the shaded grey region), but can be reproduced when alpha and carbon abundance is increased.