code: def _planck_deriv(self, lam, Teff):
          
  
          expterm = np.exp(self.h*self.c/lam/self.k/Teff)
          return 2*self.h*self.c*self.c/self.k/Teff/lam**7 * (expterm-1)**-2 * (self.h*self.c*expterm-5*lam*self.k*Teff*(expterm-1))
docs: Computes the derivative of the monochromatic blackbody intensity using
          the Planck function.
  
          @lam: wavelength in m
          @Teff: effective temperature in K
  
          Returns: the derivative of monochromatic blackbody intensity