English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We use observations from the Interstellar Boundary Explorer (IBEX) andUlysses to explore the possibility that the interstellar neutral helium flowingthrough the inner solar system possesses an intrinsic non-Maxwellian velocitydistribution. In fitting the IBEX and Ulysses data, we experiment with both akappa distribution and a bi-Maxwellian, instead of the usual Maxwellianassumption. The kappa distribution does not improve the quality of fit toeither the IBEX or Ulysses data, and we find lower limits to the kappaparameter of kappa>12.1 and kappa>6.0 from the IBEX and Ulysses analyses,respectively. In contrast, we do find evidence that a bi-Maxwellian improvesfit quality. For IBEX, there is a clear preferred bi-Maxwellian solution withT_perp/T_par=0.62+/-0.11 oriented about an axis direction with eclipticcoordinates (lambda_axis,b_axis)=(57.2+/-8.9 deg,-1.6+/-5.9 deg). The Ulyssesdata provide support for this result, albeit with lower statisticalsignificance. The axis direction is close to the ISM flow direction, in aheliocentric rest frame, and is therefore unlikely to be indicative of velocitydistribution asymmetries intrinsic to the ISM. It is far more likely that theseresults indicate the presence of asymmetries induced by interactions in theouter heliosphere.

Evidence for Asymmetry in the Velocity Distribution of the Interstellar Neutral Helium Flow Observed by IBEX and Ulysses