Calibration of Hubble Space Telescope WFPC2 Emission-Line Filters

Abstract

The results of calibration of the primary emission-line filters of the Hubble Space Telescope WFPC2 are presented in a form which allows observers to easily calculate emission-line surface brightnesses for Hα, Hβ, [O III] λ5007, and [N II] λ6583. The Hα and [N II] filters pass both lines in such a way that observations in both are necessary to obtain good isolation of either line. We establish that determination of the strength of the underlying continuum can be important, especially in H II regions. We express cautionary notes against overly simple interpretations of the signal from filters selected to isolate lines at 4363, 6300, and 6717+6731 Å. Finally, we use this calibration to recommend guidelines for the selection of emission-line filters on future HST instruments.