Observations of helium in the interplanetary/interstellar wind - The solar-wake effect

Abstract

Extraterrestrial neutral helium radiation was detected by the thin-film/photomultiplier photometers (170-1500 A) on board the STP 72-1 satellite. The observed sky map of extraterrestrial He I 584 A radiation is in excellent agreement with the expectations of the interstellar wind theory: the helium is gravitationally focused producing a downwind wake. Observations were analyzed by a computer-coded radiation-scattering model. The appearance of a neutral helium-radiation maximum in the downstream direction and a hydrogen-radiation maximum upstream is accurately accounted for by models of solar radiation scattered from a gas cloud moving through the interplanetary system.