Very Local Interstellar Medium Revealed by a Complete Solar Cycle of Interstellar Neutral Helium Observations with IBEX

Swaczyna, P.; Kubiak, M. A.; Bzowski, M.; Bower, J.; Fuselier, S. A.; Galli, A.; Heirtzler, D.; McComas, D. J.; Möbius, E.; Rahmanifard, F.; Schwadron, N. A. (2022). Very Local Interstellar Medium Revealed by a Complete Solar Cycle of Interstellar Neutral Helium Observations with IBEX. Astrophysical journal - supplement series, 259(2), p. 42. Institute of Physics Publishing IOP 10.3847/1538-4365/ac4bde

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The IBEX-Lo instrument on board the Interstellar Boundary Explorer (IBEX) mission samples interstellar neutral (ISN) helium atoms penetrating the heliosphere from the very local interstellar medium (VLISM). In this study, we analyze the IBEX-Lo ISN helium observations covering a complete solar cycle, from 2009 through 2020 using a comprehensive uncertainty analysis including statistical and systematic sources. We employ the Warsaw Test Particle Model to simulate ISN helium fluxes at IBEX, which are subsequently compared with the observed count rate in the three lowest energy steps of IBEX-Lo. The χ2 analysis shows that the ISN helium flows from ecliptic $\left(\lambda ,\beta \right)=(255\buildrel{\circ}\over{.} 59\pm 0\buildrel{\circ}\over{.} 23,5\buildrel{\circ}\over{.} 14\pm 0\buildrel{\circ}\over{.} 08)$, with speed vHP = 25.86 ± 0.21 km s−1 and temperature THP = 7450 ±140 K at the heliopause. Accounting for gravitational attraction and elastic collisions, the ISN helium speed and temperature in the pristine VLISM far from the heliopause are vVLISM = 25.9 km s−1 and TVLISM = 6150 K, respectively. The time evolution of the ISN helium fluxes at 1 au over 12 yr suggests significant changes in the IBEX-Lo detection efficiency, higher ionization rates of ISN helium atoms in the heliosphere than assumed in the model, or an additional unaccounted for signal source in the analyzed observations. Nevertheless, we do not find any indication of the evolution of the derived parameters of ISN helium over the period analyzed. Finally, we argue that the continued operation of IBEX-Lo to overlap with the Interstellar Mapping and Acceleration Probe will be pivotal in tracking possible physical changes in the VLISM.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute
08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences

UniBE Contributor:

Galli, A

Subjects:

500 Science > 520 Astronomy
500 Science > 530 Physics
600 Technology > 620 Engineering
000 Computer science, knowledge & systems

ISSN:

0067-0049

Publisher:

Institute of Physics Publishing IOP

Language:

English

Submitter:

Dora Ursula Zimmerer

Date Deposited:

11 Aug 2022 14:20

Last Modified:

05 Dec 2022 16:22

Publisher DOI:

10.3847/1538-4365/ac4bde

BORIS DOI:

10.48350/171741

URI:

https://boris.unibe.ch/id/eprint/171741

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