EUVE Science Highlights -
January 15, 1999
EUVE Science Highlights -
January 15, 1999
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Slide 1 of 2
Dr. Brian Flynn of the University of California, Berkeley reports that Interstellar He passes through the distant heliopause unaffected (relative to H) and transits the inner solar system where it can be detected by EUVE via resonance scattering of solar HeI Ly-( emission at 584 Å. During the EUVE all-sky survey from 1992 to 1993, EUVE routinely detected this local interstellar "wind". Due to EUVE's motion within this medium, the wind's appearance depends strongly on the time of year and look direction. For instance, when EUVE was moving in the upwind direction in February 1993, the scanners detected the gravitational enhancement of He density downwind from the Sun (labeled Gravitational Focussing in the figure) at a scan azimuth of ~270o. Near the ecliptic poles (scan angles of ~0 and ~180o), where the relative speed of the interstellar He wind and the geocorona are at a minimum, extinction by the geocoronal He takes place. Model fits to the all-sky survey data have provided estimates of some interstellar He parameters, such as temperature, speed, and flow direction. In order to search for spatial variability in the interstellar He, we have repeated the February 1993 portion of the all-sky survey in February 1998. Some results from a comparison of the data sets are given above.