Physics – Plasma Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsh23d..08m&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SH23D-08
Physics
Plasma Physics
[2126] Interplanetary Physics / Heliosphere/Interstellar Medium Interactions, [2144] Interplanetary Physics / Interstellar Gas, [2194] Interplanetary Physics / Instruments And Techniques, [7837] Space Plasma Physics / Neutral Particles
Scientific paper
Due to the motion of the Sun relative to its neighborhood, the neutral gas of the local interstellar cloud (LIC) flows through the inner heliosphere where it is subject to ionization, the Sun’s gravity, and radiation pressure. Observing the resulting spatial and angular flow distribution of several interstellar gas species with direct neutral atom imaging techniques in the inner heliosphere provides us with the most detailed information on physical conditions of the LIC and its interaction with the outer heliosheath. The primary interstellar neutral gas flow reveals the original LIC velocity distribution, while a secondary flow component from charge exchange with outer heliosheath ions that are diverted around the heliosphere carries information on deceleration, deflection, and heating of the interstellar plasma in the boundary layer. IBEX has observed neutral gas distributions for almost two years, with two primary interstellar flow passages in winter 2009 and 2010, of several interstellar species, notably H, He, O, and Ne, with its triple-coincidence time-of-flight IBEX-Lo sensor. To unravel LIC parameters from these flow distributions, observations are compared with test-particle simulations and an analytical calculation of the gas trajectories, which is simplified by IBEX observations at almost exactly perihelion of the flow. Both comparison methods result in the best agreement for a small parameter range, with the inflow speed functionally tied to the inflow direction in longitude, approximately bounded by two parameter sets, with identical results for 2009 and 2010. The first set features the same interstellar flow vector as found previously for He in a concerted effort at the International Space Science Institute (ISSI)(Moebius et al.; Witte, A&A, Vol 426, 2004), but with substantially higher temperature, and the second set shows the same temperature, but coming from ≈6° larger longitude and at ≈4 km/s slower speed. Detailed comparison of the distributions indicates a slight preference for a different flow vector and the same temperature. For heavy species an approximate 50/50 split between O and Ne is found, which leads to the identical tempera-ture as for He, when the flow distribution is analyzed analogous to He, indicating an isothermal LIC for all species. Both the He and O distribution contain a substantial secondary component, which arrives from noticeably higher latitude than the primary flow, indicating a diversion of the interstellar flow.
Bochsler Peter A.
Bzowski Maciej
Funsten Herbert O.
Fuselier Stephen A.
Heirtzler D.
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