xdust.graindist.composition

The composition library is built on the superclass Composition, which holds the optical constants and material density [g cm^-3] of a grain composition type.

Premade composition types

• CmDrude – Drude approximation, treating the grain as a mass of free electrons

• CmSilicate – astronomical silicates (Draine 2003)

• CmGraphite – graphite (Draine 2003)

Composition

class xdust.graindist.composition.Composition

Bases: object

Composition class for storing information about grain material

cmtype

Label for the compound.

Type:

str

rho

Density of the material [g cm^-3].

Type:

float

citation

Citation for the optical constants loaded.

Type:

str

wavel

Wavelength grid for optical constants.

Type:

astropy.units.Quantity

revals

Real part of the complex index of refraction.

Type:

numpy.ndarray

imvals

Imaginary part of the complex index of refraction.

Type:

numpy.ndarray

cm(x)

Returns the complex index of refraction using Python complex numbers

Parameters:

x (astropy.units.Quantity or numpy.ndarray) – Wavelength or energy; if an astropy.units.Quantity, converted to the same units as self.wavel; if a plain array, keV units are assumed.

Returns:

Complex index of refraction \(n = n_r + i n_i\).

Return type:

complex or numpy.ndarray of complex

ip(x)

Interpolate over the input wavelength grid to get the imaginary part of the complex index of refraction.

Parameters:

x (astropy.units.Quantity or numpy.ndarray) – Wavelength or energy; if an astropy.units.Quantity, converted to the same units as self.wavel; if a plain array, keV units are assumed.

Returns:

np.interp(x, self.wavel, self.imvals, left=0.0, right=0.0)

Return type:

numpy.ndarray

plot(ax, lam=None, rppart=True, impart=True, xunit=None, label='')

Plots the different parts of the complex index of refraction on a matplotlib axis

Parameters:

• ax (matplotlib.pyplot.Axes) – The axes on which to plot.

• lam (astropy.units.Quantity or numpy.ndarray, optional) – If None, plots using the default self.wavel grid; otherwise interpolates onto the provided grid. Plain arrays are assumed to be in keV.

• rppart (bool) – If True (default), plot the real part \(|Re(m)-1|\).

• impart (bool) – If True (default), plot the imaginary part \(Im(m)\).

• xunit (str, optional) – Unit string for the x-axis. Defaults to self.wavel.unit.

• label (str) – Prefix string appended to legend labels.

rp(x)

Interpolate over the input wavelength grid to get the real part of the complex index of refraction.

Parameters:

x (astropy.units.Quantity or numpy.ndarray) – Wavelength or energy; if an astropy.units.Quantity, converted to the same units as self.wavel; if a plain array, keV units are assumed.

Returns:

np.interp(x, self.wavel, self.revals, left=1.0, right=1.0)

Return type:

numpy.ndarray

CmDrude

class xdust.graindist.composition.CmDrude(rho=3.0)

Bases: Composition

Optical constants under the Drude approximation.

ip(x)

Gives the imaginary part of the complex index of refraction under the Drude approximation.

Parameters:

x (astropy.units.Quantity or numpy.ndarray) – Wavelength or energy; plain arrays are assumed to be in keV.

Returns:

0.0 for scalar input; array of zeros matching the length of x for array input.

Return type:

float or numpy.ndarray

rp(x)

Calculate the real part of the complex index of refraction under the Drude approximation.

Parameters:

x (astropy.units.Quantity or numpy.ndarray) – Wavelength or energy; plain arrays are assumed to be in keV.

Returns:

\(1 + (\rho / 2 m_p)(r_e / 2\pi)\lambda^2\)

Return type:

numpy.ndarray

CmSilicate

class xdust.graindist.composition.CmSilicate(rho=3.8)

Bases: Composition

Optical constants for Silicate from Draine (2003), ApJ 598, 1026

CmGraphite

class xdust.graindist.composition.CmGraphite(rho=2.2, size='big', orient='perp')

Bases: Composition

Optical constants for Graphite from Draine (2003), ApJ 598, 1026

size

'big' gives results for 0.1 um sized graphite grains at 20 K; 'small' gives results for 0.01 um sized grains at 20 K.

Type:

str

orient

'perp' gives results for E-field perpendicular to the c-axis; 'para' gives results for E-field parallel to the c-axis.

Type:

str