@staticmethod
def _polynomial(x, y, p):
    """Polynomial that can be fitted to an isochrone.

        Args:
            x: Colours of points in isochrone.
            y: Magnitudes of points in isochrone.
            p: Coefficients for polynomial.

        Returns:
            Evaluated polynomial.
        """
    return p[0] + p[1] * x + p[2] * y + p[3] * x * x + p[4] * y * y + p[5
        ] * x * y + p[6] * x * x * x + p[7] * x * x * y + p[8] * x * y * y + p[
        9] * y * y * y
