Heliospheric boundary in the backscattered solar Lyman-alpha radiation: analysis of Voyager-1/UVS data
Résumé
UVS instrument onboard Voyager-1 has been performing measurements of the
backscattered solar Lyman-alpha emissions for more than 35 years. Since 2003
when the scan platform movements were stopped, it measures Lyman-alpha radiation in one line
of sight close to the upwind direction. The most interesting feature of these data is radial
dependence of measured intensity. Namely, Voyager-1 data shows almost
constant intensity (after correction for the solar flux variations) between 90 and 115 AU, while the
numerical models of global heliosphere and radiative transfer predict decreasing
intensity. Between 115 AU (beginning of 2011) and about 124 AU (beginning of 2013),
the data show a decrease of the intensity again. This last period corresponds to motion of
Voyager-1 in the transition region (Krimigis et al., 2011) before crossing the heliopause
at 122 AU in August, 2012 (Stone et al., 2013). This behavior of the Lyman-alpha intensity observed by Voyager can be a tracer of complicated structure of the heliospheric boundary. Plasma instruments onboard Voyagers provide information about charged
component of the solar and interstellar winds and energetic particles, while only the UVS
data for the Lyman-alpha intensity reflect the distribution of the neutral hydrogen
component. Therefore, interpretation of Voyager-1/UVS measurements is critical to
understand the complete picture of the interaction between the solar
wind and surrounding interstellar matter. In this work we will present preliminary results of
analysis of Voyager-1/UVS data in the frame of the kinetic-MHD heliospheric model and radiative transfer code. Possible scenarios for hydrogen distribution consis
tent with Voyager-1 data will be proposed.