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Abstract Infrared (IR) studies of asymptotic giant branch (AGB) stars are critical to our understanding of the formation of cosmic dust. In this investigation, we explore the mid- to far-IR emission of the oxygen-rich AGB star RT Virginis. This optically thin dusty environment has unusual spectral features when compared to other stars in its class. To explore this enigmatic object we use the one-dimensional radiative transfer modeling code DUSTY. Modeled spectra are compared with observations from the Infrared Space Observatory, InfraRed Astronomical Satellite, the Herschel Space Observatory, and a host of other sources to determine the properties of RT Vir's circumstellar material. Our models suggest a set of two distant and cool dust shells at low optical depths (τ_V,inner= 0.16,τ_V,outer= 0.06), with inner dust temperaturesT₁= 330 K,T₃= 94 K. Overall, these dust shells exhibit a chemical composition consistent with dust typically found around O-rich AGB stars. However, the distribution of materials differs significantly. The inner shell consists of a mixture of silicates, Al₂O₃, FeO, and Fe, while the outer shell primarily contains crystalline Al₂O₃polymorphs. This chemical change is indicative of two distinct epochs of dust formation around RT Vir. These changes in dust composition are driven by either changes in the pressure–temperature conditions around the star or by a decrease in the C/O ratio due to hot-bottom burning. 

ABSTRACT We present the second data release for the H i-MaNGA programme of H i follow-up observations for the SDSS-IV MaNGA survey. This release contains measurements for 3669 unique galaxies, combining 2108 Green Bank Telescope observations with an updated crossmatch of the MaNGA sample with the ALFALFA survey. We combine these data with MaNGA spectroscopic measurements to examine relationships between H i-to-stellar mass ratio ($${\rm M_{H\, {\small I}}/{M_*}}$$) and average ISM/star formation properties probed by optical emission lines. $${\rm M_{H\, {\small I}}/{M_*}}$$ is very weakly correlated with the equivalent width of H α, implying a loose connection between the instantaneous star formation rate and the H i reservoir, although the link between $${\rm M_{H\, {\small I}}/{M_*}}$$ and star formation strengthens when averaged even over only moderate time-scales (∼30 Myr). Galaxies with elevated H i depletion times have enhanced [O i]/H α and depressed H α surface brightness, consistent with more H i residing in a diffuse and/or shock-heated phase that is less capable of condensing into molecular clouds. Of all optical lines, $${\rm M_{H\, {\small I}}/{M_*}}$$ correlates most strongly with oxygen equivalent width, EW(O), which is likely a result of the existing correlation between $${\rm M_{H\, {\small I}}/{M_*}}$$ and gas-phase metallicity. Residuals in the $${\rm M_{H\, {\small I}}/{M_*}}$$−EW(O) relation are again correlated with [O i]/H α and H α surface brightness, suggesting they are also driven by variations in the fraction of diffuse and/or shock-heated gas. We recover the strong anticorrelation between $${\rm M_{H\, {\small I}}/{M_*}}$$ and gas-phase metallicity seen in previous studies. We also find a relationship between $${\rm M_{H\, {\small I}}/{M_*}}$$ and [O i]6302/H α, suggesting that higher fractions of diffuse and/or shock-heated gas are more prevalent in gas-rich galaxies.