Reexamining the Lyman Continuum in Starburst Galaxies Observed with the Hopkins Ultraviolet Telescope

We have reevaluated the constraints on the Lyman continuum emission from four starburst galaxies observed with the Hopkins Ultraviolet Telescope (HUT) during the Astro-2 mission. Applying a detailed model of the absorption by interstellar gases in our Galaxy, and using the latest HUT data products, we find upper limits to the redshifted Lyman continuum that are less restrictive than those reported previously. Well-determined astrophysical and instrumental effects permit 2 σ upper limits no tighter than 5.2%, 11%, 57%, and 3.2% to be set on the escape fraction of Lyman continuum photons from IRAS 08339+6517, Mrk 1267, Mrk 66, and Mrk 496, respectively. Absorption from undetected interstellar components (including H2) or modulation of the emergent spectrum by gas or dust in the parent galaxy could allow the true escape fractions to exceed these revised upper limits.