There are three different types of models: average, R(V)+ dependent prediction, and shape fitting.
These models provide averages from the literature with the ability to interpolate between the observed data points. Models are provided for the Milky Way for the optical (Bastiaansen 1992), ultraviolet through near-infrared (Gordon, Cartlege, & Clayton 2009) and near- and mid-infrared (Rieke & Lebofsky 1985; Indebetouw et al. 2005; Chiar & Tielens 2006; Fritz et al. 2011) and the Magellanic Clouds (Gordon et al. 2003).
For the Milky Way for the ultraviolet through near-infrared, one of the R(V) dependent models with R(V) = 3.1 (see next section) is often used for the Milky Way ‘average’.
R(V) (+ other variables) dependent prediction models¶
These models provide predictions of the shape of the dust extinction given input variable(s).
The R(V) dependent models include CCM89 the original such model (Cardelli, Clayton, and Mathis 1989), the O94 model that updates the optical portion of the CCM89 model (O’Donnell 1994), and the F99 model (Fitzpatrick 1999) updated as F04 (Fitzpatrick 2004), These models are based on the average behavior of extinction in the Milky Way as a function of R(V). The M14 model refines the optical portion of the CCM89 model (Maiz Apellaniz et al. 2014), was developed for the LMC but has been shown valid elsewhere in the Milky Way.
In addition, the (R(V), f_A) two parameter relationship from Gordon et al. (2016) is included. This model is based on the average behavior of extinction in the Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud.
These models provide literature grain models interpolated between the computed data points. These dust grain models are based on fitting observed extinction curves and other observed properties of dust (e.g., abundances, IR emission). Models are provided for the Milky Way calculated for the X-ray to the submm.
Shape fitting models¶
These models are used to fit the detailed shape of dust extinction curves. The FM90 (Fitzpatrick & Mass 1990) model uses 6 parameters to fit the shape of the ultraviolet extinction. The P92 (Pei 1992) uses 19 parameters to fit the shape of the X-ray to far-infrared extinction. The G21 (Gordon et al. 2021) models uses 10 parameters to fit the shape of the NIR/MIR 1-40 micron extinction.