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Title: REVISITING ULYSSES OBSERVATIONS OF INTERSTELLAR HELIUM

Abstract

We report the results of a comprehensive reanalysis of Ulysses observations of interstellar He atoms flowing through the solar system, the goal being to reassess the interstellar He flow vector and to search for evidence of variability in this vector. We find no evidence that the He beam seen by Ulysses changes at all from 1994-2007. The direction of flow changes by no more than ∼0.°3 and the speed by no more than ∼0.3 km s{sup –1}. A global fit to all acceptable He beam maps from 1994-2007 yields the following He flow parameters: V {sub ISM} = 26.08 ± 0.21 km s{sup –1}, λ = 75.54 ± 0.°19, β = –5.44 ± 0.°24, and T = 7260 ± 270 K; where λ and β are the ecliptic longitude and latitude direction in J2000 coordinates. The flow vector is consistent with the original analysis of the Ulysses team, but our temperature is significantly higher. The higher temperature somewhat mitigates a discrepancy that exists in the He flow parameters measured by Ulysses and the Interstellar Boundary Explorer, but does not resolve it entirely. Using a novel technique to infer photoionization loss rates directly from Ulysses data, we estimate a density of n {sub He} = 0.0196more » ± 0.0033 cm{sup –3} in the interstellar medium.« less

Authors:
 [1];  [2];  [3]
  1. Naval Research Laboratory, Space Science Division, Washington, DC 20375 (United States)
  2. Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755 (United States)
  3. Max-Planck-Institute for Solar System Research, Katlenburg-Lindau D-37191 (Germany)
Publication Date:
OSTI Identifier:
22521389
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 801; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ATOMS; DENSITY; HELIOSPHERE; HELIUM; INTERSTELLAR SPACE; PHOTOIONIZATION; SOLAR SYSTEM; SUN; VELOCITY

Citation Formats

Wood, Brian E., Müller, Hans-Reinhard, and Witte, Manfred, E-mail: brian.wood@nrl.navy.mil. REVISITING ULYSSES OBSERVATIONS OF INTERSTELLAR HELIUM. United States: N. p., 2015. Web. doi:10.1088/0004-637X/801/1/62.
Wood, Brian E., Müller, Hans-Reinhard, & Witte, Manfred, E-mail: brian.wood@nrl.navy.mil. REVISITING ULYSSES OBSERVATIONS OF INTERSTELLAR HELIUM. United States. doi:10.1088/0004-637X/801/1/62.
Wood, Brian E., Müller, Hans-Reinhard, and Witte, Manfred, E-mail: brian.wood@nrl.navy.mil. Sun . "REVISITING ULYSSES OBSERVATIONS OF INTERSTELLAR HELIUM". United States. doi:10.1088/0004-637X/801/1/62.
@article{osti_22521389,
title = {REVISITING ULYSSES OBSERVATIONS OF INTERSTELLAR HELIUM},
author = {Wood, Brian E. and Müller, Hans-Reinhard and Witte, Manfred, E-mail: brian.wood@nrl.navy.mil},
abstractNote = {We report the results of a comprehensive reanalysis of Ulysses observations of interstellar He atoms flowing through the solar system, the goal being to reassess the interstellar He flow vector and to search for evidence of variability in this vector. We find no evidence that the He beam seen by Ulysses changes at all from 1994-2007. The direction of flow changes by no more than ∼0.°3 and the speed by no more than ∼0.3 km s{sup –1}. A global fit to all acceptable He beam maps from 1994-2007 yields the following He flow parameters: V {sub ISM} = 26.08 ± 0.21 km s{sup –1}, λ = 75.54 ± 0.°19, β = –5.44 ± 0.°24, and T = 7260 ± 270 K; where λ and β are the ecliptic longitude and latitude direction in J2000 coordinates. The flow vector is consistent with the original analysis of the Ulysses team, but our temperature is significantly higher. The higher temperature somewhat mitigates a discrepancy that exists in the He flow parameters measured by Ulysses and the Interstellar Boundary Explorer, but does not resolve it entirely. Using a novel technique to infer photoionization loss rates directly from Ulysses data, we estimate a density of n {sub He} = 0.0196 ± 0.0033 cm{sup –3} in the interstellar medium.},
doi = {10.1088/0004-637X/801/1/62},
journal = {Astrophysical Journal},
number = 1,
volume = 801,
place = {United States},
year = {Sun Mar 01 00:00:00 EST 2015},
month = {Sun Mar 01 00:00:00 EST 2015}
}