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In dusty cool-star outflow or ejection events around asymptotic giant branch (AGB) or R Coronae Borealis or RCB-like stars, dust is accelerated by radiation from the star and coupled to the gas via collisional drag forces. It has recently been shown that such dust-gas mixtures are unstable to a super-class of instabilities called the resonant drag instabilities (RDIs), which promote dust clustering. We therefore consider idealized simulations of the RDIs operating on a spectrum of dust grain sizes subject to radiative acceleration (allowing for different grain optical properties), coupled to the gas with a realistic drag law, including or excluding the effects of magnetic fields and charged grains, and calculate for the first time how the RDIs could contribute to observed variability. We show that the RDIs naturally produce significant variations (spatially and temporally) ($\sim 10\!-\!20{{\ \rm per\ cent}}$ 1 σ-level) in the extinction, corresponding to $\sim 0.1\!-\!1\,$mag level in the stellar types above, on time-scales of order months to a year. The fluctuations are surprisingly robust to the assumed size of the source as they are dominated by large-scale modes, which also means their spatial structure could be resolved in some nearby systems. We also quantify how this produces variations in the line-of-sight grain size-distribution. All of these variations are similar to those observed, suggesting that the RDIs may play a key role driving observed spatial and temporal variability in dust extinction within dusty outflow/ejection events around cool stars. We further propose that the measured variations in grain sizes could directly be used to identify the presence of the RDIs in close by systems with observations.

Recent studies have shown that live (not decayed) radioactive 60Fe is present in deep-ocean samples, Antarctic snow, lunar regolith, and cosmic rays. 60Fe represents supernova (SN) ejecta deposited in the Solar system around $3 \, \rm Myr$ ago, and recently an earlier pulse ${\approx}7 \ \rm Myr$ ago has been found. These data point to one or multiple near-Earth SN explosions that presumably participated in the formation of the Local Bubble. We explore this theory using 3D high-resolution smooth-particle hydrodynamical simulations of isolated SNe with ejecta tracers in a uniform interstellar medium (ISM). The simulation allows us to trace the SN ejecta in gas form and those eject in dust grains that are entrained with the gas. We consider two cases of diffused ejecta: when the ejecta are well-mixed in the shock and when they are not. In the latter case, we find that these ejecta remain far behind the forward shock, limiting the distance to which entrained ejecta can be delivered to ≈100 pc in an ISM with $n_\mathrm{H}=0.1\,\, \rm cm^{-3}$ mean hydrogen density. We show that the intensity and the duration of 60Fe accretion depend on the ISM density and the trajectory of the Solar system. Furthermore, we show the possibility of reproducing the two observed peaks in 60Fe concentration with this model by assuming two linear trajectories for the Solar system with 30-km s−1 velocity. The fact that we can reproduce the two observed peaks further supports the theory that the 60Fe signal was originated from near-Earth SNe.