Double Detonations on a Moving Mesh with Cattails: Characterizing Early Reddening in SNe Ia

Type Ia supernovae are useful as cosmological distance indicators and are significant sources of chemical enrichment in galaxies, but much about their origins remains uncertain. The double detonation explosion mechanism is one promising model for these transients. We present a suite of thermonuclear hydrodynamic double detonation models of sub-Chandrasekhar mass white dwarfs spanning thin to thick helium shells. Thin shell models produce light curves and spectra consistent with normal Type Ia supernovae, and thicker shell models have early time luminosity bumps from radioactive ashes in the shell and early reddening in color sometimes observed in peculiar Type I supernovae. The reddening is due to line blanketing from heavy elements produced in the shell detonation encompassing the central emission. We perform the computations using Cattails, a moving mesh nuclear hydrodynamics code introduced in this work. After carrying out subsequent radiative transfer calculations using the Sedona code, we relate the time of early reddening to the mass of the initial helium shell. We also consider how the relation changes as a function of total mass as well as how the peak brightness depends on the total mass. Finally, we provide a series of fitting functions that can be used to estimate the mass of the shell consistent with an observation of reddening in the early color evolution of a type Ia supernova.