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FRINATEK-Fri mat.,naturv.,tek

Tracing the impact of evolved stars on the Galactic chemical enrichment

Alternative title: Hvordan stjerner i sene stadier av sitt liv innvirker på den galaktiske kjemiske sammensetningen

Awarded: NOK 8.0 mill.

Stars are the universe’s element factories. A large fraction of elements in the periodic table, including the essential ones for the formation of rocky planets and life in the universe such as carbon, oxygen, and nitrogen, are produced during the star’s life cycle through stellar nucleosynthesis. The synthesised elements will then be blown out into space during late phases of stellar evolution. Consequently, understanding the chemical network active in evolved stars is essential to understand the chemical evolution of galaxies. Our project aims to deepen the knowledge on the late phases of evolution of sun-like stars and their role in the Galactic chemical evolution.  Fluorine,  the essential element for the maintenance of solidity of our bones and teeth, is among few elements whose cosmic origin is still unknown. We aim to use state-of-the-art observational facilities such as Atacama large millimetre array (ALMA) and upgraded chemical models to trace possible sites of Fluorine productions in our Galaxy which was not possible before. This will shed light on the long-lasting question on the origin of fluorine.  In addition, we aim to make a more realistic chemical picture of the outflow around evolved solar-type stars by including UV radiation from stellar chromospheric activity and hot binary companions in the chemical models. This will enable us to assess the impact of UV radiation on the efficiency of the stellar dust formation and isotopic chemistry of evolved stars. The impact of stellar chromospheric emission has not been considered in any chemical models of evolved stars so far. This missing factor might be able to answer some of the unsolved discrepancies between observations and theoretical models such as the high efficient dust formation in evolved stars. Our goal is to provide the most complete view of the effect of the internal UV radiation on the late phases of stellar evolution and dust formation.

Solar-type stars eject a substantial amount of heavy elements and dust particles to the interstellar medium through strong stellar winds at late phases of stellar evolution, known as the asymptotic giant branch (AGB) phase. They, therefore, significantly influence the chemical composition of galaxies. To trace the enrichment of the interstellar medium by outflows of evolved stars, it is critical to understand the chemical networks active in them. In this research proposal, I target two main gaps in our knowledge that can be significantly advanced with the current observational facilities, new laboratory molecular data, and upgraded chemical models. These concern the role of AGB stars in the production of fluorine, the essential element for the maintenance of solidity of our bones and teeth, in our Galaxy and the impact of a chromospheric UV radiation field on the chemistry and dust-formation process around AGB stars. This project aims to make a more realistic picture of the recycled materials and stardust from evolved stars by considering the impact of internal UV radiation in the chemical models. The great novelty of this project is the use of new promising high-spectral and -spatial Atacama large millimetre array (ALMA) observations towards a well-selected sample and upgraded radiative transfer and chemical models.

Funding scheme:

FRINATEK-Fri mat.,naturv.,tek