FLASH Talks: Clues to galaxy evolution from chemical abundances of stars in the Galactic center & He II Emission from Wolf-Rayet Stars: a New Dust Attenuation Measure in Star-forming Galaxies
Friday, 04 February 2022 noon — 1 p.m. MST
Brian Thorsbro (Lund Obs) & Rebecca Minsley (Steward)
Brian Thorsbro, Lund University
Clues to galaxy evolution from chemical abundances of stars in the Galactic center
We present a detailed study of the composition of 20 M giants in the Galactic center with 15 of them confirmed to be in the nuclear star cluster. As a control sample we have also observed 7 M giants in the Milky Way disk with similar stellar parameters. We report the first silicon abundance trends versus [Fe/H] for stars in the Galactic center. While finding a disk/bulge like trend at subsolar metallicities, we find that [Si/Fe] is enhanced at supersolar metallicities. We speculate on possible enrichment scenarios to explain such a trend, however, there is a definite need for follow-up studies. Further, we present preliminary results on high resolution spectroscopy performed on stars in the nuclear star clusters that have been identified as possible intermediate-age stars.
Rebecca Minsley, Steward
He II Emission from Wolf-Rayet Stars: a New Dust Attenuation Measure in Star-forming Galaxies
We present a novel method to measure the interstellar reddening in star-forming galaxies. The ability to robustly determine galaxy properties such as masses, ages and star-formation rates is critically limited by the ability to accurately measure dust attenuation. Dust reddening is often characterized by comparing observations to models of either nebular recombination-lines or the UV continuum. Here, we use a new technique to measure dust reddening by exploiting emission line features originate in the stellar winds of Wolf-Rayet stars. The He II 1640 and 4686 features are recombination lines formed in these winds, which have an intrinsic ratio primarily determined by atomic physics. As a result, the two spectral lines can be used to look at stellar reddening similarly to how the Balmer lines probe reddening of gas emission. These lines have been observed in galaxies within the local universe out to a redshift of 3, and will be detected at higher redshifts with JWST. Using this third dust probe as a compliment to both the Balmer decrement and the stellar absorption provides a significant improvement to our understanding of dust attenuation by allowing us to study the stellar and nebular components separately. It also allows us to test the effects of dust at different stellar age and mass regimes. We present new optical and UV spectra from star-forming regions in eight nearby star-forming galaxies obtained for this project with HST STIS and discuss first results.
FLASH Talks are scientific talks for the staff at NOIRLab and the University of Arizona's Steward Observatory.
If you or a collaborator are interested in presenting at FLASH please get in touch. All FLASH talks are virtual for the foreseeable future, so feel free to suggest speakers from outside of Tucson!