SH53C-09
The local interstellar medium based on ISN He observations with Ulysses and IBEX and future IMAP measurements
Friday, 18 December 2015: 15:16
2011 (Moscone West)
Maciej Bzowski1, Pawel Swaczyna1, Marzena A. Kubiak2, Justyna M Sokol1, Stephen A Fuselier3, Andre Galli4, David Heirtzler5, Harald Kucharek6, Trevor Leonard6, David J McComas3, Eberhard Moebius7, Nathan Schwadron8 and Peter Wurz4, (1)Space Research Center Polish Academy of Sciences, Warszawa, Poland, (2)Space Research Center Polish Academy of Sciences, Warsaw, Poland, (3)Southwest Research Institute, San Antonio, TX, United States, (4)University of Bern, Bern, Switzerland, (5)University of New Hampshire, Durham, NH, United States, (6)University of New Hampshire Main Campus, Durham, NH, United States, (7)University of New Hampshire, Institute for the Study of Earth, Oceans and Space, and Department of Physics, Durham, NH, United States, (8)University of New Hampshire Main Campus, Space Science Center, Durham, NH, United States
Abstract:
Direct sampling is an efficient and effective method for studying the local neutral interstellar matter. With first measurements performed in the 1990s by GAS experiment onboard Ulysses, followed by IBEX observations since 2009, we have now a ~20 year long coverage. These observations provide a unique sample of interstellar matter from a spatial region with the dimensions close to the mean free path for atom-ion and atom-atom collisions in the local interstellar medium. Recent analyses of available GAS and IBEX data have resulted in a consolidation of the flow velocity vector and gas temperature of ISN He ahead of the heliosphere. The present GAS and IBEX velocity vectors are in agreement with the determination based on the first two Ulysses ISN observation seasons, but the temperature is markedly higher, by at least 1000 K, than the original determination. In addition, IBEX observations revealed the existence of an additional population of neutral He, dubbed the Warm Breeze, which is likely the secondary population of He produced in the outer heliosheath. We will briefly present the analysis of GAS observations from all three Ulysses orbits and focus on a detailed analysis of IBEX observations from the first six ISN He observation seasons. The velocity vector and temperature obtained from individual IBEX observation seasons vary around the global best-fit values, which is most likely due to statistical fluctuations in the data. An important aspect of the ISN gas studies is the Warm Breeze, which partly overlaps with the ISN population on the sky. Therefore it must be studied in parallel with the ISN gas. Observations of ISN He could provide insight into various hypothetical departures of ISN He from the ideal Maxwell-Boltzmann distribution, but a significant portion of the sky most interesting in this respect is blocked by the local magnetospheric signal, which will not interfere with the observations planned for the IMAP mission.
