Characteristics of the helium component of the local interstellar medium

Extreme ultraviolet instruments on the Solrad 11 B satellite observed helium in the local interstellar medium (LISM) flowing through the solar system through resonantly scattered 584 A solar radiation. Since this satellite orbited the Earth at 130,000 km altitude and, thus, was far removed from the geocoronal airglow, reliable measurements over many directions at a given time were made. As a result these data, together with ''hot gas'' density-resonance scatter computations and our previous results, permit accurate determination of quite narrow ranges of LISM velocity, V = 22--28 km s/sup -1/, and temperature, T = 9,000--15,000 K. The derived LISM helium density of 1.1--2.7 x 10/sup -2/ cm/sup -3/, when compared with the derived density of the inflowing LISM hydrogen 4--6 x 10/sup -2/ cm/sup -3/, suggests that the local interstellar gas is substantially ionized.