A new analytical scattering phase function for interstellar dust

Context: Properly modelling scattering by interstellar dust grains requires a good characterisation of the phase function. The Henyey-Greenstein function has become standard for describing anisotropic grains, but it is poor representation real outside optical range. Aims: We investigate alternatives that would allow properties to be described. Our goal find balance between realism and complexity: should flexible enough provide an accurate fit over wide wavelength range, simple easy handle, especially in context radiative transfer calculations. Methods: various analytical functions corresponding BARE-GR-S model, one most popular commonly adopted models dust. weigh accuracy against number free parameters functions. Results: confirm poorly describe particularly at ultraviolet (UV) wavelengths, with relative differences up 50%. Draine alleviates this problem near-infrared (NIR) not UV. two-term Reynolds-McCormick function, recently advocated light nanoscale materials aquatic media, describes data very well, its five are degenerate. propose simpler ultraspherical-2 (TTU2) also provides excellent entire UV-NIR (Abridged)