We have computed atomic structure and both radiative and collision rate data for a range of ions, as motivated by proposed observational identifications (Sr, Y, Z, Te, W). These new data have been incorporated into atomic models used for our radiative transfer to quantify their impact on early phase spectra. Using these new atomic data we have also been able to quantify requirements for ejected masses of particular ions that would be required, if observed features are correctly attributed to these species.
Using the high quality data on the kilonova AT2017gfo, features are shown to evolve rapidly, even hour-by-hour, due to rapid recombination transitions. Our work also indicates the prominent 1µm P Cygni line in AT2017gfo, which appeared suddenly at approximately 1.17 days, is inconsistent with a He I identification based on its temporal evolution, and reinforces its interpretation as Sr II because the emergence time and early spectral shape of this feature are shown to be consistent with Sr II, providing a direct measurement of the ejecta's ionisation temperature from the Sr III to Sr II recombination under LTE conditions. This derived ionisation temperature was found to be highly consistent with the emitted blackbody radiation temperature, and AT2017gfo appeared isotropic in temperature during the initial days post-merger. Our work also reveals evidence for a fast kilonova ejecta component reaching velocities of 0.40–0.45c and highlights that temporal modelling and high-cadence observations are crucial for constraining ejecta properties and physics.
We performed a large number of neutron star merger simulations modeling all channels of mass ejection and analyzed their nucleosynthesis outcome. Those data were further processed by radiative transfer tools to obtain synthetic spectra for comparison to observational data.
We designed and completed procurement for three new experimental photoabsorption setups, and are making progress on the 4th setup. The first three experiments cover the extreme ultraviolet, visible, near and mid-infrared spectral regions, and the fourth setup, which is under design and final procurement, covers the vacuum ultraviolet to blue spectral region. The visible-NIR experiment has delivered new spectral data, between 700 nm and 1100 nm, on neutral and singly-ionised Y, Zr, Nb, Lu, Hf and Ta. We have designed and are in the process of implementing an integrated experimental control and data reporting system, to support access to the large volumes of experimental spectral data we expect to generate.
