Hubble Science in the 2030s White Paper: High-Contrast Optical and UV Spectroscopy with HST/STIS

The Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope currently stands as the sole space-based astronomical facility providing visible-light coronagraphic imaging -- and the only facility anywhere that can perform both visible- and ultraviolet-light coronagraphic spectroscopy. In imaging, STIS offers unparalleled stability that rivals the performance of ground-based direct imaging in the optical, and a wide field of view that will complement the upcoming capabilities of Roman coronagraphy. STIS also has the capability for direct high-contrast visible and ultraviolet spectroscopy via two occulting bars in its 52'' times 0.2'' spectroscopic slit. By placing a bright astrophysical source behind an occulting bar, it is possible to use the STIS visible and NUV/FUV gratings to obtain spatially-resolved spectra of faint environments and companions, covering wavelengths from 1150-10,300 at resolutions of R about500-10, 000. In this white paper, we detail the use cases and performance of this under-utilized mode, with starlight subtraction enabling visible light spectral contrasts of about10-4-10-5. We describe the promise of STIS coronagraphic spectroscopy for a wide variety of astrophysical applications -- planetary and brown dwarf companions, circumstellar disks, young stellar objects, evolved stars and binaries, and active galactic nuclei/galaxy host environments -- throughout the 2030s. STIS high-contrast UV spectroscopy in particular could provide transformative science while pathfinding both techniques and observational studies for the Habitable Worlds Observatory.