Cosmic Origins Spectrograph Observations of the Chemical Composition of LMC N132D

TL;DR

This study uses Hubble's Cosmic Origins Spectrograph to analyze the chemical composition and velocity structure of an oxygen-rich knot in the supernova remnant N132D, revealing detailed elemental abundances and physical conditions.

Contribution

First ultraviolet spectral resolution of N132D's oxygen-rich knot, enabling detailed analysis of its chemical and velocity structure.

Findings

No nitrogen detected in N132D.

Multiple carbon species at different velocities.

Silicon and helium associated with the oxygen-rich knot.

Abstract

We present new far-ultraviolet spectra of an oxygen-rich knot in the Large Magellanic Cloud supernova remnant N132D, obtained with the Hubble Space Telescope/Cosmic Origins Spectrograph. Moderate resolution (v~200 km/s) spectra in the HST far-ultraviolet bandpass (1150 - 1750 A) show emission from several ionization states of oxygen as well as trace amounts of other species. We use the improvements in sensitivity and resolving power offered by COS to separate contributions from different velocity components within the remnant, as well as emission from different species within the oxygen-rich knot itself. This is the first time that compositional and velocity structure in the ultraviolet emission lines from N132D has been resolved, and we use this to assess the chemical composition of the remnant. No nitrogen is detected in N132D and multiple carbon species are found at velocities inconsistent with the main oxygen component. We find helium and silicon to be associated with the oxygen-rich knot, and use the reddening-corrected line strengths of OIII], OIV], OV, and SiIV to constrain the composition and physical characteristics of this oxygen-rich knot. We find that models with a silicon-to-oxygen abundance ratio of N(Si)/N(O) = 0.01 can reproduce the observed emission for a shock velocity of ~130 km/s, implying a mass of ~50 solar masses for the N132D progenitor star.