Title

INVESTIGATING THE INTERSTELLAR AND HELIOSPHERIC HEAVY NEUTRAL ATOMS WITH IBEX-LO

Date of Award

Spring 2016

Project Type

Dissertation

Program or Major

Physics

Degree Name

Doctor of Philosophy

First Advisor

Harald Kucharek

Second Advisor

Charlie Farrugia

Third Advisor

Eberhard Moebius

Abstract

The imaging technique of energetic neutral atoms (ENAs) is a very useful diagnostic tool to investigate the space plasma environments including the interstellar environment. In this dissertation, we examine the observations of the heavy ENAs (He, O, and Ne) during the winter-spring seasons (early December to early June) in 2009-2011 with the IBEX- Lo sensor on board Interstellar Boundary Explorer (IBEX). We concentrate our efforts on determining a refined Ne/O abundance ratio in the gas phase of the local interstellar cloud (LIC) to understand the nuclear evolution in our Galaxy. We corrected the derivation for determining the Ne/O abundance ratio at Earth’s orbit and adopted time-dependent survival probabilities to determine the Ne/O abundance ratio at the heliospheric termination shock. Based on the typical filtration factors in the heliosheath and the ionization fractions in the LIC, we determined the Ne/O abundance ratio to be 0.33 ± 0.07 in the gas phase of the LIC. Furthermore, we investigated the directional distributions of the primary and secondary interstellar neutral atoms in the all-sky ENA map. We verified that the measured O emissions in the energy range of 170-790 eV are composed of the primary ISN O gas and secondary ISN O population. We use signal-to-noise filter to determine the background level, the confidence limit method (CLM) to obtain the statistical significances of the O emissions, and the cluster analysis method to group pixels into regions of neutral emission with the same statistical properties. For the first time, we generated sputtering corrected all-sky maps for the primary and secondary ISN He and O populations. For the O map, we also applied the CLM to compensate for the low counting statistics. Using these sputtering corrected maps, we found that the longitude of the maximum secondary population is within 99◦ − 119◦ for He and 89◦ − 100◦ for O at Earth’s orbit. Our results indicate that the inflow longitude of the secondary populations deviates from the inflow longitude of the ISN gas.

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