EUVE Detection of the Local Interstellar Wind via Resonance Scattering of Solar He I 584 Angstroms

We present initial results from EUVE measurements of interplanetary and geocoronal He I 584 Angstroms emission made during the all-sky survey. The data consist of count rates from the tin quadrants (520--750 Angstroms) of Scanner C obtained over a 1 year period from July 1992 to July 1993. During this period, EUVE was in survey mode so that the scanners made 360(deg) sweeps of the sky in a plane perpendicular to the Sun-Earth line. The interplanetary He I signal is morphologically consistent with previous observations, such as Prognoz 6 (Dalaudier et al. 1984, A&A, v134). However, unlike the Prognoz 6 data, the EUVE measurements were made from low Earth orbit (512 km) and so contain geocoronal emission as well. As a result, along sight lines where the relative speed between the interplanetary wind and the Earth is at a minimum, absorption of the interplanetary signal by the geocorona occurs. We anticipate model fits to our data to yield: (1) interplanetary He parameters; (2) solar He I Lyalpha line information; and (3) geocoronal He column abundance and temperature. This work is supported by NASA contract NAS5-29298.