Observed perturbations of the velocity distribution of interstellar hydrogen atoms in the solar system with Prognoz Lyman-alpha measurements

International audienceObservations of the interplanetary Lyman α emission made at five different places in the solar system with high apogee satellites Prognoz 5 and Prognoz 6 are reported. This Lyα emission is the result of resonance scattering of solar photons by H atoms of the local interstellar medium (LISM) flowing in the solar system at the velocity - Vw and the spectral profile is an image of the velocity distribution of the atoms. A hydrogen absorption cell was used to analyze the spectral profile, the variation of Doppler shift with looking direction providing its spectral scanning. A first estimate of the LISM temperature is derived, T ≅ 8000K, and also an approximate location of Vw in fair agreement with previous measurements. The observed variation of the heating effect is of 3000K, and is independent of the existence of a potential galactic background in the vicinity of the Lyα wavelength. An upper limit of this background is found to be 15 Rayleigh