Semi-regular red giants as distance indicators

Context. Semi-regular variables (SRVs) are similar to Miras in brightness, and they also follow one or more period–luminosity relations (PLRs), though not necessarily the same as Miras. As potential standard candles challenging than because of their smaller variability amplitudes less regular light curves, but substantially numerous especially promising for probing old stellar populations. Aims. We aim characterise SRVs, specifically focusing on connection with Miras, order prepare ground investigating distance indicators. Methods. examine SRVs Magellanic Clouds from OGLE-III observations, data Gaia 2MASS. After cleaning sample periods unrelated pulsation, we classify each source by chemical type combination pulsation modes. results terms global photometric properties. Results. identify four SRV groups that fit general evolutionary scenario predicted theory. dominated fundamental-mode very if mono-periodic. They further split into two subgroups, which follows sequence period–amplitude diagrams, without discontinuity. Conclusions. The similarities between suggest latter can be adopted indicators a way is complementary use former, thereby at least doubling available number long-period (LPVs) suitable traditional amplitude-based separation appropriate, physically sound criterion should involve periods. While this would require comparatively longer time-series, expected become accessible coming years even weak sources thanks current future large-scale surveys. table reclassified LPVs made public.