Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh23b1958l&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SH23B-1958
Physics
[2126] Interplanetary Physics / Heliosphere/Interstellar Medium Interactions, [2144] Interplanetary Physics / Interstellar Gas, [2151] Interplanetary Physics / Neutral Particles
Scientific paper
Observations of the neutral interstellar gas flow distributions at the Earth's orbit provide the most detailed information on the physical parameters (flow direction, flow velocity, and temperature) of the surrounding interstellar medium (ISM) and the interaction with the heliospheric boundary. The Interstellar Boundary Explorer (IBEX) has observed interstellar neutral H, He, O, and Ne. For the often low counting statistics of the minor species, fitting the model distributions using a maximum likelihood method has substantial advantages over least square fitting procedures. Here, we evaluate the ISM flow observations with an analytical model of the flow, which is greatly simplified when analyzing the flow trajectories at their perihelion. The IBEX configuration, with the spin axis oriented along the Earth-Sun line at the beginning of each orbit, naturally provides observations near the perihelion of the interstellar trajectories. However, over the course of the 7.5-day IBEX orbit around the Earth, the spin axis pointing drifts away from the Sun and the ISM flow observables, such as ISM peak rate and location in latitude, vary slowly over the course of the orbit. Therefore, these observables are interpolated or extrapolated to the location where the spin axis is aligned with the Sun-Earth line in the ecliptic for comparison with the analytical model. From the results of the maximum likelihood fits we are able to deduce, among others, the location of the observed ISM flow maximum and the latitude of the ISM distribution peak as function of observer ecliptic longitude. The application of the maximum likelihood method to IBEX observations will be described along with how the results are used in the comparison with the analytical ISM flow model.
Bochsler Peter A.
Bzowski Maciej
Fuselier Stephen A.
Heirtzler D.
Kubiak M. A.
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