# fit_upper_harmonic¶

photutils.isophote.fit_upper_harmonic(phi, intensities, order)[source]

Fit upper harmonic function to a set of (angle, intensity) pairs.

With order set to 3 or 4, the resulting amplitudes, divided by the semimajor axis length and local gradient, measure the deviations from perfect ellipticity.

The harmonic function that is fit is:

$y(phi, order) = y0 + An*\sin(order*phi) + Bn*\cos(order*phi)$
Parameters
phifloat or ndarray

The angle(s) along the elliptical path, going towards the positive y axis, starting coincident with the position angle. That is, the angles are defined from the semimajor axis that lies in the positive x quadrant.

intensitiesndarray

The intensities measured along the elliptical path, at the angles defined by the phi parameter.

orderint

The order of the harmonic to be fitted.

Returns
y0, An, Bnfloat

The fitted harmonic values.