Emission line extinction mechanism

[BabisDaoutis]

Hi,

I was running some models with the FSPS to test the attenuation and extinction. I set the extinction parameter dust_type = 0 for all models. The first model has dust1 = 0.7 and dust2 = 0.3, while for the second I tried dust1 = 0.35 and dust2 = 0.15 (all the other parameters were the same). I noticed that there is a slight difference in the luminosities of the emission lines produced from these two runs. I was wondering the following:

1) What is the exact extinction mechanism applied to the emission lines? 2) What is the exact attenuation mechanism applied to UV radiation from the stellar populations? 3) How can I control the extinction applied to the emission lines and the UV radiation from the stars separately?

Best, Babis

[bd-j]

Hi @BabisDaoutis

The attenuation model is based on the Charlot & Fall 2000 two component model. Briefly, when add_neb_emission=True and nebemlineinspec=True the emission lines (and nebular continuum) are added to the spectra of 'young' stars, and then the lines and young stellar continuum are attenuated by e^(-dust1 (lambda/5500)^dust1_index). The result is added to the spectra of the 'old' stars and the sum is further attenuated by e^(-dust2 k_lambda) where k_lambda is the shape of the attenuation curve (a power-law for dust_type=0). So you'd expect to see the emission lines be different for different amounts of dust2 or dust1.

The physical picture is that the young stars that are powering the nebular emission would be attenuated by the same dust that affects the nebular continuum itself. There is no way to attenuate the nebular emission and the young starlight separately.