Mikako

Title: ALMA observations of supernova 1987A – mixing, nucleosynthesis and dynamics of the ejecta

We present a molecular line survey for supernova 1987A, using the Atacama Large Millimetre/submillimetre Array (ALMA). We detected the CO, SiO, HCO+ and SO molecular lines from the ejecta. Those molecules can probe three different aspects of the SN 1987A ejecta:

1. Footprints of mixing and dynamics in the early days after the supernova explosion,
2. Molecular chemistry in the last twenty-five years
3. Explosive nuclear synthesis, using isotopologues, hence isotope ratios

The extent of mixing after supernova explosions is still not well understood. Molecules can provide a new tool to probe this: microscopic mixing stirs the elements from different layers of nuclear-reaction zones in the stellar core, opening the possibility to form molecules with elements from different nuclear-burning zones. This process should have increased the abundance of HCO+, making it feasible now for ALMA to detect them.

Our new ALMA observations have revealed several interesting features of the molecular gas. For instance, the SiO molecular lines clearly show dips in the line profile, while the CO lines do not. The different line profiles suggest that SiO and CO are spatially distributed at different locations. This could potentially be caused by different dynamics taking place immediately after the explosion, as SN hydrodynamical simulations suggest.

ALMA spectra contain lines of isotopologues, which are molecules composed of atoms with different isotopes, and allow us to estimate the isotope ratios. Our upper limits of 28Si/29Si and 28Si/30Si are consistent with theoretically predicted values for SN 1987A. However, the ratios are at least a factor of two larger than isotopes measured in SN-associated pre-solar grains. Such thing could support the theory that neutron-rich isotopes are produced less efficiently in low metallicity environments, such as the Large Magellanic Cloud, where SN 1987A is located.