Gas absorption cell photometer for rocket observations of local interstellar helium

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Abstract
A photometer sensitive at the 584‐Å line of HeI, incorporating a helium‐gas absorption cell, has been developed. The helium is confined at a pressure of 0.2 Torr between thin metal foil broad‐band ultraviolet filters. The cell contains sufficient helium to absorb 584‐Å radiation scattered from atmospheric helium. The ratio of fluxes seen with cell full and cell empty provides a valuable datum for fitting models of the local interstellar medium, which is independent of solar 584‐Å flux, interstellar helium density, and photometer sensitivity.