New measurement of the upwind interplanetary hydrogen velocity as observed by the Hubble Space Telescope
Abstract
The interplanetary hydrogen (IPH), a population of neutrals that fill the space between planets inside the heliosphere, carries the signature of the interstellar medium (ISM) and the heliospheric interface. As the incoming ISM-ionized component deflects at the heliopause, charge exchange reactions decelerate the bulk motion of the neutrals that penetrate the heliosphere. Inside the heliosphere, the IPH bulk velocity is further affected by solar gravity, radiation pressure, and ionization processes, with the latter two processes dependent on solar activity. Space-based studies of the backscattered solar Lyα emission from the IPH provide limited access to the velocity distribution. Solar cycle 23 yielded the first partial temporal map of the IPH velocity, including measurements from the Hubble Space Telescope (HST) spectrometers (Goddard High Resolution Spectrograph (GHRS) and Space Telescope Imaging Spectrograph (STIS)) and the Solar and Heliospheric Observatory/Solar Wind ANisotropies (SWAN) instrument. In a previous work, we provided an updated analysis of IPH velocity measurements from GHRS and STIS and compared these results with those of SWAN and two different time-dependent models. This study revealed a significant change in IPH velocity relative to earlier reports, because of the contamination by geocoronal oxygen that was not accounted for. As a consequence, it corrected the discrepancy with SOHO/SWAN data near solar maximum (2001) and we found that all data can be fit by the existing models to within 1σ, with the exception of SWAN observations taken at solar minimum (1997/1998). We suggested that this discrepancy at solar minimum could be due to an indirect effect of the local interstellar magnetic field, which should be included in future modelling efforts. We obtained new observation time with HST/STIS and we are presenting the analysis of these observations which have been made in April 2012.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMSH23A2222V
- Keywords:
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- 2126 INTERPLANETARY PHYSICS / Heliosphere/interstellar medium interactions