How to Choose a Model¶
The dust_extinction package provides a suite of dust extinction models.
Which model to use can depend on the wavelength range of interest, the expected
type of extinction, or some other property.
Average Models¶
Simple Average Curves¶
These are straightforward averages of observed extinction curves. They are the
simplest models and include models for the MW
(GCC09_MWAvg), the LMC
(G03_LMCAvg,
G03_LMC2) and the SMC
(G03_SMCBar).
One often used alternative to these straight average models is to use one of the parameter dependent models with the average R(V) value. For the Milky Way, the usual average used is R(V) = 3.1.
| Model | x range | wavelength range | galaxy |
|---|---|---|---|
| GCC09_MWAvg | 0.3 - 10.96 | 0.0912 - 3.3 | MW |
| G03_LMCAvg | 0.3 - 10.0 | 0.1 - 3.3 | LMC |
| G03_LMC2 | 0.3 - 10.0 | 0.1 - 3.3 | LMC (30 Dor) |
| G03_SMCBar | 0.3 - 10.0 | 0.1 - 3.3 | SMC |
Parameter Dependent Average Curves¶
The models that are dependent on parameters provide average curves that account for overall changes in the extinction curve shapes. For example, the average behavior of Milky Way extinction curves has been shown to be dependent on R(V) = A(V)/E(B-V). R(V) roughly tracks with the average dust grain size.
The most general model is G16 as this
model encompasses the average measured behavior of extinction curves in the MW,
LMC, and SMC. The G16 model reduces
to the F99 model with fA=
1.0. If only MW type extinction is expected, then the
F20 model should be considered as it
is based on spectroscopic extinction curves in the optical and ultraviolet and
significantly more extinction curves than the
CCM89 or
O94 models.
| Model | Parameters | x range [1/micron] | wavelength range [micron] | galaxy |
|---|---|---|---|---|
| CCM89 | R(V) | 0.3 - 10.0 | 0.1 - 3.3 | MW |
| O94 | R(V) | 0.3 - 10.0 | 0.1 - 3.3 | MW |
| F99, F04 | R(V) | 0.3 - 10.0 | 0.1 - 3.3 | MW |
| VCG04 | R(V) | 3.3 - 8.0 | 0.125 - 0.31 | MW |
| GCC09 | R(V) | 3.3 - 11.0 | 0.091 - 0.31 | MW |
| M14 | R_5495 | 0.3 - 3.3 | 0.31 - 3.3 | MW, LMC |
| G16 | R(V)_A, f_A | 0.3 - 10.0 | 0.1 - 3.3 | MW, LMC, SMC |
| F99, F04 | R(V) | 0.3 - 8.7 | 0.115 - 3.3 | MW |
Notes¶
The GCC09 model is the only
model that applies all the way to 912 A, but has the limitation that it
only applies to the UV spectral region (not derived in the NIR/Optical).
The M14 models focus on refining
models in the optical, and use the
CCM89 models for the NIR and the UV.
The M14 models use
R_5495 = A(5485)/E(4405-5495), the spectroscopic equivalent to
band-integrated R(V); see the paper for discussion. Because of a spurious
feature in the near UV caused by smoothly tying their optical to the
CCM89 UV, only the NIR and
optical portions of the M14
models are provided here.
Shape Models¶
The models that focus on describing the full extinction curve shape are usually
used to fit measured extinction curves. These models allow features in the
extinction curve to be measured (e.g., 2175 A bump or 10 micron silicate
feature). The P92 is the most
general as it covers the a very broad wavelength range. The
FM90 model has been extensively used,
but only covers the UV wavelength range.
| Model | x range | wavelength range | # of parameters |
|---|---|---|---|
| FM90 | 3.13 - 11.0 | 0.0912 - 0.32 | 6 |
| P92 | 0.001 - 1000 | 0.001 - 1000 | 19 (24 possible) |