Interplanetary Lyman α background and the heliospheric interface

Details Interplanetary Lyman α background and the heliospheric interface Interplanetary Lyman α background and the heliospheric interface

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aipc..858..354q&link_type=abstract

PHYSICS OF THE INNER HELIOSHEATH: Voyager Observations, Theory, and Future Prospects; 5th Annual IGPP International Astrophysics

Astronomy and Astrophysics

Astrophysics

Interplanetary Dust And Gas, Heliopause And Solar Wind Termination, Solar Cycle Variations

Scientific paper

We present some recent measurements of the interplanetary Lyman α background which show a clear signature of the heliospheric interface.
The Voyager 1 Ultraviolet Spectrometer has measured the variation of the upwind intensity from 1993 to 2006. The derived radial variation of the intensity is clearly slower than what is expected from a hot model computation. This shows that the hydrogen number density increases ahead of the spacecraft, toward the upwind direction. The data also show an abrupt change of slope in 1998 when the Voyager 1 spacecraft was at 65 AU from the sun. This may be linked to temporal variations induced at the heliospheric interface by the variations of solar activity.
Interplanetary Lyman α line profiles measured at one AU from the sun also show a clear signature of the heliospheric interface. The SWAN instrument on-board the SOHO spacecraft has studied the line profiles between 1996 and 2002. It was found that the variations seen in line of sight velocities from solar minimum to solar maximum have a larger amplitude than what is derived from hot model computations. The observed features can be better understood when considering that some of the hydrogen atoms crossing the interface region are slowed down and heated. These results are in good agreement with the present models of the interface.
Independent spectral observations made by the Hubble Space Telescope in 1995-2001 confirm the SWAN/SOHO measurements.

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