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We present results of studying star-forming rings in six lenticular galaxies obtained with the narrow-band photometry in the H and [N II] 6583 emission lines using the MaNGaL tunable-filter mapper at the 2.5-m telescope of CMO of SAI MSU. The gas excitation mechanism estimated from the relation of the H and [N II] 6583 line fluxes occurred to be inhomogeneous along the ring: three outer rings have narrow segments of position angles, in which shocks waves dominate in the ring. Since the nature of the rings is most likely accretionary, the location of shock excitation in the outer rings indicates the direction of arrival of the external gas inflow. Star formation events in the rings are probably quite brief and effective: we mainly observe homogeneous sub-solar metallicity of the gas close to the level of local saturation of the gas chemical evolution in the star formation process and switching of the localization of the star-forming sites on a time scale of about 100 Myr. In NGC 932, we have caught the very beginning of the external gas accretion: there is still little of it in the galaxy, and the metallicity of the gas in the star-forming ring has not yet reached saturation. [ABSTRACT FROM AUTHOR]

Abstract—Using the MaNGaL tunable-filter photometer at the 2.5-m telescope of the Caucasian Mountain Observatory of the Sternberg Astronomical Institute of Lomonosov Moscow State University, we studied star formation in an early-type gas-rich galaxy, which was until now considered to be elliptical,—NGC 5173. The gas has probably been accreted in the recent past by the galaxy from a direction inclined to its disk. Star formation that we observe now has led in the past 400 Myr to the formation of compact massive clusters with shock excitation of gas around them—a star formation behavior corresponding to what is usually observed in the interacting Antennae-like galaxies. In combination with the almost solar metallicity of the gas, this allows us to conclude that NGC 5173 has assimilate a very gas-rich companion with a mass of at least 10–20% of its own stellar mass. [ABSTRACT FROM AUTHOR]