ИСТИНА

Outer stellar rings are a common feature of lenticular galaxy disks: according to the latest statistics by Comeron et al. (2014), half of all S0s have outer stellar rings. Meantime, the bar frequency falls just toward this morphological type: according to Laurikainen et al. (2011, 2013), only 35% of all S0s demonstrate some signs of bar presence in the NIR while among spirals this fraction is 80%. These two opposite tendencies provoke some doubts about the resonance origin of a bulk of outer rings. The outer rings in lenticular galaxies may be either starforming ones or rather old. We have undertaken spectral study of a small sample of the S0s with the outer rings seen in UV. Spectral-line diagnostics demonstrate a variety of excitation mechanisms for the outer starforming rings: their ionized gas is excited by young stars or by shock waves in equal fractions. When we can estimate the oxygen abundance, it is always close to the solar one that is unexpected taking into account large radial distances of the rings. The gas kinematics is often decoupled from the stellar one. I discuss possible origin of the outer ring structures in S0 galaxies and their role as a signature of the evolution paths of this morphological type.