Voyager 1/UVS Lyman α Measurements at the Distant Heliosphere (90-130 AU): Unknown Source of Additional Emission
Abstract
In this work, we present for the first time the Lyman α intensities measured by Voyager 1/UVS in 2003-2014 (at 90-130 AU from the Sun). During this period Voyager 1 measured the Lyman α emission in the outer heliosphere at an almost fixed direction close to the upwind (i.e." toward the interstellar flow). The data show an unexpected behavior in 2003-2009: the ratio of observed intensity to the solar Lyman α flux is almost constant. Numerical modeling of these data is performed in the frame of a state-of-the-art self-consistent kinetic-MHD model of the heliospheric interface. The model results, for various interstellar parameters, predict a monotonic decrease of intensity not seen in the data. We propose two possible scenarios that explain the data qualitatively. The first is the formation of a dense layer of hydrogen atoms near the heliopause. Such a layer would provide an additional backscattered Doppler-shifted Lyman α emission, which is not absorbed inside the heliosphere and may be observed by Voyager. About 35 R of intensity from the layer is needed. The second scenario is an external nonheliospheric Lyman α component, which could be galactic or extragalactic. Our parametric study shows that ∼25 R of additional emission leads to a good qualitative agreement between the Voyager 1 data and the model results.
- Publication:
-
Journal of Geophysical Research (Space Physics)
- Pub Date:
- November 2017
- DOI:
- 10.1002/2017JA024205
- arXiv:
- arXiv:1710.07038
- Bibcode:
- 2017JGRA..12210921K
- Keywords:
-
- heliosphere;
- backscattered Lyman alpha;
- heliopause;
- interstellar hydrogen;
- radiation transfer;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- accepted in Journal of Geophysical Research: Space Physics