On the Anisotropic Velocity Distribution of Newborn Pickup Ions in the Heliosheath
The evolution of the velocity distribution of pickup ions is crucial for understanding the energetic neutral atom (ENA) fluxes observed by Interstellar Boundary Explorer. Pickup ions in the heliosheath contain two main components: those transmitted across the heliospheric termination shock and those...
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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal Letters |
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| Online Access: | https://doi.org/10.3847/2041-8213/adbc9a |
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| author | Senbei Du Merav Opher Marc Kornbleuth |
| author_facet | Senbei Du Merav Opher Marc Kornbleuth |
| author_sort | Senbei Du |
| collection | DOAJ |
| description | The evolution of the velocity distribution of pickup ions is crucial for understanding the energetic neutral atom (ENA) fluxes observed by Interstellar Boundary Explorer. Pickup ions in the heliosheath contain two main components: those transmitted across the heliospheric termination shock and those locally created within the heliosheath. In this work, we discuss the velocity distribution of the latter locally created component. We find that pickup ions created by the charge exchange of neutral solar wind (NSW) may be a significant source of the observed ENA fluxes between about 100 eV and 1 keV. Moreover, newborn pickup ions can maintain highly anisotropic velocity distribution in the heliosheath. This is because the kinetic instabilities are weak after the solar wind flow decelerates at the termination shock. Hybrid kinetic simulations show the mirror instability to be the dominant mode for conditions in the heliosheath close to the termination shock. We estimate that effects of NSW and anisotropy may enhance the expected phase space density of newborn pickup ions by more than a factor of 100. |
| format | Article |
| id | doaj-art-0068fe4e8d9c49499bc82b01dd4a390e |
| institution | OA Journals |
| issn | 2041-8205 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal Letters |
| spelling | doaj-art-0068fe4e8d9c49499bc82b01dd4a390e2025-08-20T01:54:57ZengIOP PublishingThe Astrophysical Journal Letters2041-82052025-01-019822L5910.3847/2041-8213/adbc9aOn the Anisotropic Velocity Distribution of Newborn Pickup Ions in the HeliosheathSenbei Du0https://orcid.org/0000-0003-1134-3909Merav Opher1https://orcid.org/0000-0002-8767-8273Marc Kornbleuth2https://orcid.org/0000-0002-3479-1766Center for Space Physics, Boston University , Boston, MA 02215, USA ; sdu@bu.eduCenter for Space Physics, Boston University , Boston, MA 02215, USA ; sdu@bu.edu; Astronomy Department, Boston University , Boston, MA 02215, USACenter for Space Physics, Boston University , Boston, MA 02215, USA ; sdu@bu.eduThe evolution of the velocity distribution of pickup ions is crucial for understanding the energetic neutral atom (ENA) fluxes observed by Interstellar Boundary Explorer. Pickup ions in the heliosheath contain two main components: those transmitted across the heliospheric termination shock and those locally created within the heliosheath. In this work, we discuss the velocity distribution of the latter locally created component. We find that pickup ions created by the charge exchange of neutral solar wind (NSW) may be a significant source of the observed ENA fluxes between about 100 eV and 1 keV. Moreover, newborn pickup ions can maintain highly anisotropic velocity distribution in the heliosheath. This is because the kinetic instabilities are weak after the solar wind flow decelerates at the termination shock. Hybrid kinetic simulations show the mirror instability to be the dominant mode for conditions in the heliosheath close to the termination shock. We estimate that effects of NSW and anisotropy may enhance the expected phase space density of newborn pickup ions by more than a factor of 100.https://doi.org/10.3847/2041-8213/adbc9aHeliospherePickup ionsHeliosheath |
| spellingShingle | Senbei Du Merav Opher Marc Kornbleuth On the Anisotropic Velocity Distribution of Newborn Pickup Ions in the Heliosheath The Astrophysical Journal Letters Heliosphere Pickup ions Heliosheath |
| title | On the Anisotropic Velocity Distribution of Newborn Pickup Ions in the Heliosheath |
| title_full | On the Anisotropic Velocity Distribution of Newborn Pickup Ions in the Heliosheath |
| title_fullStr | On the Anisotropic Velocity Distribution of Newborn Pickup Ions in the Heliosheath |
| title_full_unstemmed | On the Anisotropic Velocity Distribution of Newborn Pickup Ions in the Heliosheath |
| title_short | On the Anisotropic Velocity Distribution of Newborn Pickup Ions in the Heliosheath |
| title_sort | on the anisotropic velocity distribution of newborn pickup ions in the heliosheath |
| topic | Heliosphere Pickup ions Heliosheath |
| url | https://doi.org/10.3847/2041-8213/adbc9a |
| work_keys_str_mv | AT senbeidu ontheanisotropicvelocitydistributionofnewbornpickupionsintheheliosheath AT meravopher ontheanisotropicvelocitydistributionofnewbornpickupionsintheheliosheath AT marckornbleuth ontheanisotropicvelocitydistributionofnewbornpickupionsintheheliosheath |