Dust Mass and Gas Budget of the Post-Asymptotic-Giant-Branch Nebula Frosty Leo

This paper computes a self-contained budget for IRAS 09371+1212 (Frosty Leo) from published observational values, with every derived number produced by the deposited computation script. Frosty Leo is a bipolar post-asymptotic-giant-branch nebula famous for its strong ice absorption features and its bright reflection lobes. It has not yet formed a fully developed ionised planetary nebula, so its gas budget must be framed carefully: the dust mass from the infrared emission is comparatively secure, while the gas mass is traced by molecular and scattered light rather than by a bright ionised shell. The dust-to-gas comparison in such an object measures the conditions in the envelope during the brief transition off the asymptotic giant branch. The headline results are: dust_mass_Msun = 0.006; gas_mass_Msun = 0.045; dust_to_gas_ratio = 0.133; ratio_to_ISM_0p01 = 13.3; total_dust_plus_gas_Msun = 0.051; dust_temperature_K = 80. The dust mass is substantial for so compact an envelope, indicating efficient condensation during the final superwind phase. The inferred ratio is consistent with an oxygen-rich chemistry in which silicate and ice mantles carry much of the solid mass, in contrast to the carbon-rich case treated elsewhere in this set of objects. Because the object is still in transition, its budget is a snapshot of envelope assembly rather than of nebular dispersal, and the paper keeps that distinction explicit throughout. The calculation is presented with its inputs, relations and sensitivities stated openly, so that any revised distance, density or stellar parameter can be substituted and the verdict recomputed directly.