Nome
Spectral Analysis and Radiative Data for Elemental Kilonovae Identification

Código
2023.14470.PEX

Entidade Beneficiária

LIP - Laboratório de Instrumentação e Física Experimental de Partículas

Sumário do Projecto

In the last decade, it has become evident that heavy elements (above Fe) can be produced in the expanding ejecta following a binary neutron star merger (NSM). Indeed, the 2017 observation of the kilonova (astronomical transient AT 2017gfo) associated with the famous gravitational wave (GW170817) provided robust indications that lanthanides and eventually actinides were being formed. This conclusion, based on the temporal evolution of the luminosity curve from the ultraviolet/visible to the infrared region, is groundbreaking, as it is the first evidence that elements are being formed through the rapid neutron capture (r-process) mechanism proposed many decades ago. More challenging has been the identification of specific features in the luminosity curve of this event, associating them with absorption and emission lines of individual elements produced in the ejecta.In this proposal we aim at making a significant contribution the analysis of these processes , performing it in a more systematic and reliable fashion.In particular, we aim at the quantification of some key elements of the r-process that arise immediately after NSM and to understand how they evolve during the expansion. To achieve this, it will be necessary to perform spectral analysis of the observations, by simulations using radiative transfer codes grounded in robust atomic parameter databases.One current challenge in the analysis is the glaring lack of atomic data necessary for modeling the late epochs (> 4 days after the NSM) of the expansion. While it is a reasonable approximation to assume that the matter is in local thermodynamic equilibrium (LTE) and that atomic absorption processes dominate in the early hours (< 1 day after the NSM), it is not possible to assume LTE for nebular epochs (non-LTE). During these late stages, relevant processes include photoionization, ionization and excitation by electronic impact, and electronic recombination, for which the data is very scarce.Our team has extensive experience in calculating atomic parameters and simulating radiative transfer processes in stellar plasmas. The LIP team members have been working for many years on atomic parameter calculations for spectrum interpretation. In recent years, they have focused on determining opacities for modeling kilonovae in close collaboration with the Nuclear Astrophysics group at GSI, led by Dr. Gabriel Martínez-Pinedo.The GSI group will continue to collaborate on this proposal, contributing their expertise in the use and development of radiative transfer codes and interpreting the results based on their knowledge of stellar nuclear processes, particularly the r-process and related mechanisms.Therefore, we propose to calculate photoionization, ionization, and electronic collision excitation cross-sections for key r-process elements (Sr, Y, ...) using the FAC (Flexible Atomic Code) and AUTOSTRUCTURE codes, that are well-established for atomic structure calculations. The concurrent use of two independent codes aims at constraining the uncertainties in our calculations and performing sensitivity analyses in the quantification of those species. The quality of the calculations will be assessed based on the (limited) available experimental data and/or other calculations derived from more rigorous (albeit much slower) methods, such as the one implemented in the MCDFGME (Multiconfiguration Dirac-Fock and General Matrix Elements) code. Whenever possible, these data will be utilized as inputs in the optimization algorithm developed by the group in recent works to provide more reliable data. These data will serve as input for ARTIS (Atmospheric Radiative Transfer Simulator), a code that allows the simulation of radiative transfer processes, including the non-LTE regime. Through the temporal analysis of synthetic spectra from early to late epochs, we aim at not only the identication of the produced species but also to understand which ones persist during the ejecta expansion and the role of collision processes in their evolution.

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Suporte sob

Reforçar a investigação, o desenvolvimento tecnológico e a inovação

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