Calibration ofHubble Space TelescopeWFPC2 Emission‐Line Filters

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.