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Exploring the r-process in the Optical and Infrared

Presentation #548.12 in the session “Stellar Evolution and Populations”.

Published onJan 11, 2021
Exploring the r-process in the Optical and Infrared

Ultra-faint dwarf galaxies (UFDs) are faint, old, and dark matter dominated stellar systems that are ideal laboratories for studying a variety of astrophysical processes including stellar formation in metal poor environments and exchanges of stellar populations between satellite and host galaxies. One method of constraining these processes is by studying the r-process elements in stars of nearby UFDs. Studies have shown that metal-poor UFDs that exhibit an enhancement in r-process elements must have experienced a single enrichment event, such as a binary neutron star merger, in their history. Europium (Eu) is a primary r-process elements which can only be formed via the r-process. However, accurate abundances of Eu can only be determined from high resolution spectra (R > 10,000) on large telescopes (3+ meters). The purpose of this study is to use the 10-meter Gran Telescopio Canarias (GTC) to detect and analyze the infrared and optical Eu absorption lines at 4129.72, 9898.3, 10019.52 Å. Utilizing the optical multi-object NUV and optical spectrograph MEGARA, as well as the upcoming multi-object infrared spectrograph MIRADAS both on board the GTC, we show that we can make accurate measurements of Eu in multiple stars of UFD systems simultaneously. Particularly we shall present results for an interesting UFD, Canes Venatici II (CVnII), for which the chemical abundances of only 3 stars have been studied. One of the stars shows an enhanced abundance of strontium with [Sr/Fe] = 1.32. Using MEGARA, we have proposed to observe 13 stars in CVnII to measurements of Eu, Sr, and Ba to obtain a complete picture of the neutron-capture enrichment within CVn II. We are using two filters that cover a wavelength range of 3919 to 4625 Å in order to observe the Eu line at 4129 Å, a Sr line at 4215 Å, and a Ba line at 4934 Å. IR detections of r-process elements have not been made in metal-poor stars yet, and the possibility to obtain multiple measurements of stars within a UFD will lead to a better understanding of these interesting systems, including identification of enrichment events that took place in them, as well as better constraining their roles in the hierarchical formation of the Milky Way halo.

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