calculate_concentration_index

petrofit.petrosian.calculate_concentration_index(fraction_1, fraction_2, r_list, flux_list, r_petrosian, flux_err=None, r_petrosian_err=None, epsilon=2.0, epsilon_fraction=0.99, interp_kind='cubic', interp_num=5000)

Calculates Petrosian concentration index.

concentration_index = C_1_2 = 5 * np.log10( r(fraction_2) / r(fraction_1) )

Parameters:

fraction_1float

Fraction of total light enclosed by the radius in the denominator.

fraction_2float

Fraction of total light enclosed by the radius in the numerator.

r_listnumpy.array

Array of radii in pixels.

flux_listnumpy.array

Array of photometric flux values.

r_petrosianfloat

Petrosian radius

flux_errint or numpy.array, optional

Array of errors in the flux values. If None, erros are not computed even if r_petro_err is provided.

r_petrosian_errfloat, optional

1-sigma error in r_petro. If set to None and flux_err is provided, r_petro_err is assumed to be 0 when computing errors.

epsilonfloat, default=2.

Epsilon value (used to determine r_epsilon). N.B: r_epsilon = r_petrosian * epsilon`

epsilon_fraction: float, default=0.99

Fraction of total flux that is recovered by r_petrosian * epsilon.

interp_kindstr or int, optional

Specifies the kind of interpolation used on the curve of growth (i.e r_list vs flux_list)

interp_numint

Number of interpolation function sampling radii.

Returns:

r_fraction_1, r_fraction_2, concentration_index

• r_fraction_1float or np.nan

  Radius containing fraction_1 of the total flux.

• r_fraction_2: float or np.nan

  Radius containing fraction_2 of the total flux.

• concentration_indexfloat or np.nan

  Concentration index