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Title: NEUTRAL INTERSTELLAR HELIUM PARAMETERS BASED ON IBEX-Lo OBSERVATIONS AND TEST PARTICLE CALCULATIONS

Abstract

Because of its high ionization potential and weak interaction with hydrogen, neutral interstellar helium (NISHe) is almost unaffected at the heliospheric interface with the interstellar medium and freely enters the solar system. This second most abundant species provides some of the best information on the characteristics of the interstellar gas in the local interstellar cloud. The Interstellar Boundary Explorer (IBEX) is the second mission to directly detect NISHe. We present a comparison between recent IBEX NISHe observations and simulations carried out using a well-tested quantitative simulation code. Simulation and observation results compare well for times when measured fluxes are dominated by NISHe (and contributions from other species are small). Differences between simulations and observations indicate a previously undetected secondary population of neutral helium, likely produced by interaction of interstellar helium with plasma in the outer heliosheath. Interstellar neutral parameters are statistically different from previous in situ results obtained mostly from the GAS/Ulysses experiment, but they do agree with the local interstellar flow vector obtained from studies of interstellar absorption: the newly established flow direction is ecliptic longitude 79.{sup 0}2, latitude -5.{sup 0}1, the velocity is {approx}22.8 km s{sup -1}, and the temperature is 6200 K. These new results imply amore » markedly lower absolute velocity of the gas and thus significantly lower dynamic pressure on the boundaries of the heliosphere and different orientation of the Hydrogen Deflection Plane compared to prior results from Ulysses. A different orientation of this plane also suggests a new geometry of the interstellar magnetic field, and the lower dynamic pressure calls for a compensation by other components of the pressure balance, most likely a higher density of interstellar plasma and strength of interstellar magnetic field.« less

Authors:
; ; ;  [1]; ; ; ; ; ;  [2];  [3];  [4]
  1. Space Research Centre PAS, Warsaw (Poland)
  2. Space Science Center and Department of Physics, University of New Hampshire, Durham, NH (United States)
  3. Haystack Observatory, Massachusetts Institute of Technology, Westford, MA (United States)
  4. Lockheed Martin, Space Physics Lab, 3251 Hanover Street, Palo Alto, CA 94304 (United States)
Publication Date:
OSTI Identifier:
22048041
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal, Supplement Series
Additional Journal Information:
Journal Volume: 198; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0067-0049
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ASTROPHYSICS; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; DENSITY; HELIOSPHERE; HELIUM; HYDROGEN; INTERSTELLAR MAGNETIC FIELDS; INTERSTELLAR SPACE; IONIZATION POTENTIAL; ORIENTATION; PLASMA; SOLAR SYSTEM; SUN; TEST PARTICLES; ULTRAVIOLET RADIATION; VELOCITY

Citation Formats

Bzowski, M, Kubiak, M A, Sokol, J M, Hlond, M, Moebius, E, Bochsler, P, Leonard, T, Heirtzler, D, Kucharek, H, Schwadron, N A, Crew, G B, Fuselier, S A, and McComas, D. J., E-mail: stephen.a.fuselier@linco.com. NEUTRAL INTERSTELLAR HELIUM PARAMETERS BASED ON IBEX-Lo OBSERVATIONS AND TEST PARTICLE CALCULATIONS. United States: N. p., 2012. Web. doi:10.1088/0067-0049/198/2/12.
Bzowski, M, Kubiak, M A, Sokol, J M, Hlond, M, Moebius, E, Bochsler, P, Leonard, T, Heirtzler, D, Kucharek, H, Schwadron, N A, Crew, G B, Fuselier, S A, & McComas, D. J., E-mail: stephen.a.fuselier@linco.com. NEUTRAL INTERSTELLAR HELIUM PARAMETERS BASED ON IBEX-Lo OBSERVATIONS AND TEST PARTICLE CALCULATIONS. United States. doi:10.1088/0067-0049/198/2/12.
Bzowski, M, Kubiak, M A, Sokol, J M, Hlond, M, Moebius, E, Bochsler, P, Leonard, T, Heirtzler, D, Kucharek, H, Schwadron, N A, Crew, G B, Fuselier, S A, and McComas, D. J., E-mail: stephen.a.fuselier@linco.com. Wed . "NEUTRAL INTERSTELLAR HELIUM PARAMETERS BASED ON IBEX-Lo OBSERVATIONS AND TEST PARTICLE CALCULATIONS". United States. doi:10.1088/0067-0049/198/2/12.
@article{osti_22048041,
title = {NEUTRAL INTERSTELLAR HELIUM PARAMETERS BASED ON IBEX-Lo OBSERVATIONS AND TEST PARTICLE CALCULATIONS},
author = {Bzowski, M and Kubiak, M A and Sokol, J M and Hlond, M and Moebius, E and Bochsler, P and Leonard, T and Heirtzler, D and Kucharek, H and Schwadron, N A and Crew, G B and Fuselier, S A and McComas, D. J., E-mail: stephen.a.fuselier@linco.com},
abstractNote = {Because of its high ionization potential and weak interaction with hydrogen, neutral interstellar helium (NISHe) is almost unaffected at the heliospheric interface with the interstellar medium and freely enters the solar system. This second most abundant species provides some of the best information on the characteristics of the interstellar gas in the local interstellar cloud. The Interstellar Boundary Explorer (IBEX) is the second mission to directly detect NISHe. We present a comparison between recent IBEX NISHe observations and simulations carried out using a well-tested quantitative simulation code. Simulation and observation results compare well for times when measured fluxes are dominated by NISHe (and contributions from other species are small). Differences between simulations and observations indicate a previously undetected secondary population of neutral helium, likely produced by interaction of interstellar helium with plasma in the outer heliosheath. Interstellar neutral parameters are statistically different from previous in situ results obtained mostly from the GAS/Ulysses experiment, but they do agree with the local interstellar flow vector obtained from studies of interstellar absorption: the newly established flow direction is ecliptic longitude 79.{sup 0}2, latitude -5.{sup 0}1, the velocity is {approx}22.8 km s{sup -1}, and the temperature is 6200 K. These new results imply a markedly lower absolute velocity of the gas and thus significantly lower dynamic pressure on the boundaries of the heliosphere and different orientation of the Hydrogen Deflection Plane compared to prior results from Ulysses. A different orientation of this plane also suggests a new geometry of the interstellar magnetic field, and the lower dynamic pressure calls for a compensation by other components of the pressure balance, most likely a higher density of interstellar plasma and strength of interstellar magnetic field.},
doi = {10.1088/0067-0049/198/2/12},
journal = {Astrophysical Journal, Supplement Series},
issn = {0067-0049},
number = 2,
volume = 198,
place = {United States},
year = {2012},
month = {2}
}