Outer heliosphere Lymanα background derived from two-shock model hydrogen distributions: application to the Voyager UVS data.

Details Outer heliosphere Lymanα background derived from two-shock model hydrogen distributions: application to the Voyager UVS data. Outer heliosphere Lymanα background derived from two-shock model hydrogen distributions: application to the Voyager UVS data.

Apr 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...308..279q&link_type=abstract

Astronomy and Astrophysics, v.308, p.279-289

Astronomy and Astrophysics

Astrophysics

19

Interplanetary Medium, Ism: General, Solar Neighbourhood, Ultraviolet: Solar System

Scientific paper

In a previous paper [Quemerais et al. 1995], we have reported the results of Lymanα measurements made by the Ultraviolet Spectrometers aboard both Voyager 1 and 2 spacecraft since 1993. We showed that comparison of the data with a radiative transfer calculation for an unperturbed interstellar hydrogen flow into the solar system revealed a systematic excess in the upwind direction. An absolute estimate of this Lymanα intensity excess yielded 10 to 15 Rayleigh for each spacecraft. Results on the outer heliospheric hydrogen distribution obtained by Baranov and Malama [1993] have been used to estimate the Lymanα intensity backscattered by neutral hydrogen atoms at large distance from the Sun. The existence of the hydrogen wall near the heliopause implies a gradient of hydrogen at large distance from the Sun which significantly affects the Lymanα glow pattern. In these new computations we have also included variations of local bulk velocity and temperature of the hydrogen distribution in the radiative transfer calculation. Although it has not been possible to find a completely satisfactory fit between the data and the Baranov-Malama models, a better agreement was found than in the case of the standard hot model, which neglects effects of charge exchange between interstellar protons and hydrogen atoms near the heliopause. On the other hand, the remaining discrepancy between the models and the data, which is found near the upwind direction, suggests that the intensity excess does not follow the simple axial symmetry used here. Because the directions of the incoming hydrogen atoms and the galactic center nearly coincide, we must alternately consider the possibility that the Lymanα intensity excess may include a component of galactic origin.

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