The 2D Distribution of Iron Rich Ejecta in the Remnant of SN 1885 in M31

TL;DR

This study uses HST ultraviolet images to map the 2D distribution of iron ejecta in the SN 1885 remnant, providing insights into the explosion mechanism and ejecta geometry of this probable Type Ia supernova.

Contribution

It presents the first detailed 2D iron distribution in SN 1885 remnant using UV absorption imaging, offering new constraints on Type Ia supernova explosion models.

Findings

Fe II distribution shows four streams extending to 10,000 km/s

Ca II absorption is concentrated in a spherical shell at 1,000-5,000 km/s

Distribution supports delayed detonation models and suggests a symmetric explosion

Abstract

We present Hubble Space Telescope (HST) ultraviolet Fe I and Fe II images of the remnant of Supernova 1885 (S And) which is observed in absorption against the bulge of the Andromeda galaxy, M31. We compare these Fe I and Fe II absorption line images to previous HST absorption images of S And, of which the highest quality and theoretically cleanest is Ca II H & K. Because the remnant is still in free expansion, these images provide a 2D look at the distribution of iron synthesized in this probable Type Ia explosion, thus providing insights and constraints for theoretical SN Ia models. The Fe I images show extended absorption offset to the east from the remnant's center as defined by Ca II images and is likely an ionization effect due to self-shielding. More significant is the remnant's apparent Fe II distribution which consists of four streams or plumes of Fe-rich material seen in absorption that extend from remnant center out to about 10,000 km/s. This is in contrast to the remnant's Ca II absorption, which is concentrated in a clumpy, roughly spherical shell at 1000 to 5000 km/s but which extends out to 12,500 km/s. The observed distributions of Ca and Fe rich ejecta in the SN 1885 remnant are consistent with delayed detonation white dwarf models. The largely spherical symmetry of the Ca-rich layer argues against a highly anisotropic explosion as might result from a violent merger of two white dwarfs.