LOSVD for the Hydra I PN sample from Fig. 1 (black histogram), compared with a simulated MSIS LOSVD (green histogram) for a Gaussian velocity distribution with σ_core = 464   km   s^-1; see text for further details. The blue-red solid line shows the combined filter transmission curve as given in Eq. (7). The vertical magenta, green and gray lines mark the systemic velocity of Hydra I, NGC 3311 and NGC 3309, respectively.