Analysis of interplanetary Lyman-alpha line profile with a hydrogen absorption cell - Theory of the Doppler angular spectral scanning method

International audienceThe use of a hydrogen absorption cell as a means of diagnostic for interstellar hydrogen is described. Through resonance scattering of solar Lyα photons, the interstellar atoms penetrating into the solar system present a Lyα emission the profile of which is an image of their velocity distribution. From the study of hydrogen Lyα profiles the temperature T of the interstellar hydrogen and the three components of the relative velocity vector Vw can be determined. The case in which the velocity distribution of H atoms in the interplanetary medium is the same Maxwell-Boltzmann distribution as at infinity (the uniform gaussian case) is completely described