NOTE: This week only, FLASH will meet in NOIRLab Room 27, not the Main Conference Room.

K. Azalee Bostroem
Insights on Massive Stars and Hydrogen-rich Supernovae from UV Spectra

While the early optical spectra of hydrogen-rich supernovae are nearly featureless, the ultraviolet (UV) is rich in metal lines, stringently constraining the density, temperature, and composition of the supernova ejecta. Additionally, signatures of interaction between the supernova ejecta and circumstellar material are also stronger in the UV than in the optical at all times, making it a much more sensitive probe of the full range of red supergiant mass loss. Despite the wealth of information in the UV,  this wavelength range remains virtually unexplored. I will present recent results of two nearby hydrogen-rich supernovae: SN 2022acko and SN 2023ixf. The FUV spectra of SN 2022acko are the earliest collected of a Type IIP supernova and show no evidence of circumstellar interaction. On the other hand, NUV observations of SN 2023ixf, show strong interaction at early times which fade over time to a nominal red supergiant wind, connecting high mass-loss rates observed in the early optical spectra to progenitor observations of a quiescent red supergiant. These observations are critical for testing models in the UV and for interpreting high-redshift supernovae from the Rubin Observatory’s LSST, the Roman Space Telescope Core Community Surveys, and JWST. Additionally, they serve as a pathfinder for the next generation of UV observatories: UVEX and the Habitable Worlds Observatory.