calculate_petrosian_r

petrofit.petrosian.calculate_petrosian_r(r_list, petrosian_list, petrosian_err=None, eta=0.2, interp_kind='cubic', interp_num=5000)

Calculate petrosian radius from photometric values using interpolation. The Petrosian radius is defined as the radius at which the petrosian profile equals eta.

Parameters:

r_listnumpy.array

Array of radii in pixels.

petrosian_listnumpy.array

Array of petrosian values at each value of area_list

petrosian_errnumpy.array

Array of 1-sigma errors in the Petrosian values.

etafloat, default=0.2

Eta is the petrosian value which defines the r_petrosian.

interp_kindstr or int, optional

Specifies the kind of interpolation as a string or as an integer specifying the order of the spline interpolator to use. If set to None, the radius is computed descretely. The string has to be one of ‘linear’, ‘nearest’, ‘nearest-up’, ‘zero’, ‘slinear’, ‘quadratic’, ‘cubic’, ‘previous’, or ‘next’. ‘zero’, ‘slinear’, ‘quadratic’ and ‘cubic’ refer to a spline interpolation of zeroth, first, second or third order; ‘previous’ and ‘next’ simply return the previous or next value of the point; ‘nearest-up’ and ‘nearest’ differ when interpolating half-integers (e.g. 0.5, 1.5) in that ‘nearest-up’ rounds up and ‘nearest’ rounds down. Default is ‘linear’.

interp_numint

Number of interpolation function sampling radii.

Returns:

r_petrofloat or numpy.nan

Petrosian radius

r_petro_errfloat or numpy.nan

1-sigma error in r_petro. Computed if petrosian_err is provided.