extinction.ccm89(wave, a_v, r_v, unit='aa', out=None)

Cardelli, Clayton & Mathis (1989) extinction function.

The parameters given in the original paper [1] are used. The claimed validity is 1250 Angstroms to 3.3 microns.

wave : numpy.ndarray (1-d)

Wavelengths or wavenumbers.

a_v : float

Scaling parameter, A_V: extinction in magnitudes at characteristic V band wavelength.

r_v : float

Ratio of total to selective extinction, A_V / E(B-V).

unit : {‘aa’, ‘invum’}, optional

Unit of wave: ‘aa’ (Angstroms) or ‘invum’ (inverse microns).

out : np.ndarray, optional

If specified, store output values in this array.

Extinction in magnitudes at each input wavelength.


In Cardelli, Clayton & Mathis (1989) the mean R_V-dependent extinction law, is parameterized as

\[<A(\lambda)/A_V> = a(x) + b(x) / R_V\]

where the coefficients a(x) and b(x) are functions of wavelength. At a wavelength of approximately 5494.5 angstroms (a characteristic wavelength for the V band), a(x) = 1 and b(x) = 0, so that A(5494.5 angstroms) = A_V. This function returns

\[A(\lambda) = A_V (a(x) + b(x) / R_V)\]


[1]Cardelli, J. A., Clayton, G. C., & Mathis, J. S. 1989, ApJ, 345, 245