Albert Sneppen: Identification of yttrium in a kilonova photosphere

Thursday 25 May 2023, 13:00 → 14:00 Europe/Stockholm

Albano 3: 6228 - Mega (22 seats) (Albano Building 3)

Neutron star mergers are believed to be a major cosmological source of rapid neutron-capture elements. However, the kilonovae associated with neutron star mergers have to date yielded only a single well-identified spectral signature: the P Cygni line of Sr II at about 1 micron in the spectra of the optical transient, AT2017gfo. Such P Cygni lines are important, because they provide significant information not just potentially on the elemental composition of the merger ejecta, but also on the velocity, geometry, and abundance stratification of the explosion. In this talk, I will present evidence for a previously unrecognised P Cygni line in the spectra of AT2017gfo that emerged several days after the explosion. We show that such a feature is actually predicted by the 4d^2--4d5p transitions in Y II in terms of central wavelength, velocity stratification, prominence of the feature and the timing of the first appearance. We will discuss the implications of this identification for the synthesis of the heaviest elements in the universe