9 papers
The galactic chemical evolution of carbon: Implications for stellar nucleosynthesis
Daniel A. Boyea, James W. Johnson, David H. Weinberg
Carbon (C) is thought to be produced by both core collapse supernovae (CCSN) and asymptotic giant branch (AGB) stars, but the relative contributions of these two sources are uncert…
Towards a measurement of the primordial helium isotope ratio
Ryan J. Cooke, James W. Johnson, Pasquier Noterdaeme +4
We report the discovery of two metastable neutral helium (He I*) absorbers in the Milky Way, and use the upgraded CRyogenic InfraRed Echelle Spectrograph on the Very Large Telescop…
Scylla at APOGEE: The Impact of Starbursts on the Chemical Evolution of the Magellanic Clouds
Ivanna Escala, Kristen B. W. McQuinn, Sten Hasselquist +11
Owing to their proximity to the Milky Way, the Large and Small Magellanic Clouds (L/SMC) uniquely probe the evolution of low-mass galaxies undergoing mutual interactions. In this w…
Challenges to the Two-Infall Scenario by Large Stellar Age Catalogs
Liam O. Dubay, Jennifer A. Johnson, James W. Johnson +1
Stars in the Milky Way disk exhibit a clear separation into two chemically distinct populations based on their [/Fe] ratios. This -bimodality is not a universal feature of…
Metals versus Non-metals: Chemical Evolution of Hydrogen and Helium Isotopes in the Milky Way
James W. Johnson, Miqaela K. Weller, Ryan J. Cooke
Star formation drives changes in the compositions of galaxies, fusing H and He into heavier nuclei. This paper investigates the differences in abundance evolution between metal and…
Constraints on Radial Gas Flows in the Milky Way Disk Revealed by Large Stellar Age Catalogs
James W. Johnson
Disk galaxies like the Milky Way are expected to experience gas flows carrying matter toward their centers. This paper investigates the role of these radial gas flows in models of…