xdust.grainpop¶

The SingleGrainPop object is used to model a population of dust grains based on three distinct properties:

the grain size distribution (see xdust.graindist.sizedist)
composition type specifying the optical constants (see xdust.graindist.composition)
the scattering physics model (see xdust.scatteringmodel)

Furthermore, the GrainPop object contains a list of SingleGrainPop objects, which can be called upon using keys, like a dictionary. Keys have to be specified when the GrainPop object is initialized.

Module provides

SingleGrainPop class
GrainPop class
Helper functions

SingleGrainPop¶

class xdust.grainpop.SingleGrainPop(dtype, cmtype, stype, shape='Sphere', md=0.0001, scatm_from_file=None, **kwargs)[source]¶

Bases: GrainDist

SingleGrainPop unifies the grain size distribution (its parent class) with extinction model calculations. It provides attributes and convenience functions for easy access to frequently needed information. Only one dust composition can be modeled at a time.

Parameters:

dtype (string or custom xdust.graindist.sizedist) – Defines the grain radius distribution, string options: ‘Grain’, ‘Powerlaw’, ‘ExpCutoff’
cmtype (string or custom xdust.graindist.composition) – Defines the optical constants and material density of the compound, string options: ‘Drude’, ‘Silicate’, ‘Graphite’
stype (string or custom xdust.scatteringmodel) – Defines what extinction model calculator to use, string options: ‘RG’ (Rayleigh-Gans), ‘Mie’ (Mie scattering)
shape (string) – Only ‘Sphere’ is supported, some day might be used to define a custom shape
md (float) – Dust mass column [g cm^-2]
scatm_from_file (string) – If provided, will read in a scattering model from a FITS file, and use the scattering model parameters and scattering properties from the file.
**kwargs – Extra inputs passed to GrainDist.__init__.

Note

If an input for scatm_from_file is provided, then the stype input will be ignored.

lam¶

wavelength or energy used for the extinction computation

Type:: astropy.units.Quantity

tau_sca¶

scattering optical depth for this grain population

Type:: numpy.ndarray float

tau_abs¶

absorption optical depth for this grain population

Type:: numpy.ndarray float

tau_ext¶

extinction (scattering + absorption) optical depth for this grain population

Type:: numpy.ndarray float

diff¶

[cm^2 ster^-1] differential scattering cross-section as a function of wavelength/energy, grain size, and angle (NE x NA x NTH)

Type:: astropy.units.Quantity

int_diff¶

[ster^-1] differential cross-section integrated over grain size distribution, \(d au/d\Omega\) (NE x NTH)

Type:: astropy.units.Quantity

GrainPop¶

class xdust.grainpop.GrainPop(gpoplist, keys=None, description='Custom_GrainPopDict')[source]¶

Bases: object

A collection of SingleGrainPop objects. Each SingleGrainPop represents a different composition (or perhaps different geometries of grain size distribution). Each SingleGrainPop object has a label string, and can be accessed in the same was as key-value pairs are accessed in a Python dictionary.

Parameters:

gpoplist (Python list of SingleGrainPop objects) – Will be paired, in order, with the values in keys
keys (Python list of strings) – Labels for each SingleGrainPop object. (Default: None, will make the keys a list of integers starting with 0)
description (string) – A description for this collection

keys¶

Labels for each SingleGrainPop object.

Type:: Python list of strings

gpoplist¶

Paired, in order, with the values in keys

Type:: Python list of SingleGrainPop objects

description¶

A description for this collection

Type:: string

lam¶

Wavelength or energy used for the extinction computation

Type:: astropy.units.Quantity

md¶

Total dust mass column [g cm^-2], sum of the md values from each SingleGrainPop in the collection

Type:: float

tau_ext¶

Total extinction optical depth as a function of wavelength / energy

Type:: numpy.ndarray

tau_sca¶

Total scattering optical depth as a function of wavelength / energy

Type:: numpy.ndarray

tau_abs¶

Total absorption optical depth as a function of wavelength / energy

Type:: numpy.ndarray

Helper functions¶

xdust.grainpop.make_MRN(amin=0.005, amax=0.3, p=3.5, md=0.0001, fsil=0.6, **kwargs)[source]¶

Builds a xdust.grainpop object describing an MRN dust grain size distribution, which is a mixture of silicate and graphite grains. Applies the 1/3 parallel, 2/3 perpendicular assumption of graphite grain orientations.

Parameters:

amin (astropy.units.Quantity or float) – Minimum grain radius; if a float, micron units assumed
amax (astropy.units.Quantity or float) – Maximum grain radius; if a float, micron units assumed
p (float) – Powerlaw slope for grain size distribution
md (float) – Dust mass column [g cm^-2]
fsil (float) – Fraction of dust mass in silicate grains
**kwargs – Passed to graindist.sizedist.Powerlaw().

Returns:

A xdust.grainpop with keys 'sil', 'gra_para', and 'gra_perp' for the silicate, graphite parallel, and graphite perpendicular grain populations, respectively.

Return type:

GrainPop

xdust.grainpop.make_MRN_RGDrude(amin=0.005, amax=0.3, p=3.5, rho=3.0, md=0.0001, **kwargs)[source]¶

Builds a SingleGrainPop object describing an MRN dust grain size distribution, but uses Rayleigh-Gans scattering with the Drude approximation, which approximates the dust grain as a sphere of free electrons.

Parameters:

amin (astropy.units.Quantity or float) – Minimum grain radius; if a float, micron units assumed
amax (astropy.units.Quantity or float) – Maximum grain radius; if a float, micron units assumed
p (float) – Powerlaw slope for grain size distribution
rho (float) – Density of the dust grain material [g cm^-3]
md (float) – Dust mass column [g cm^-2]
**kwargs – Passed to graindist.sizedist.Powerlaw().

Returns:

A SingleGrainPop using the 'RG' scattering model and 'Drude' composition.

Return type:

SingleGrainPop