Internal and External Alignment of Carbonaceous Grains within the Radiative Torque Paradigm
We study the internal and external alignment of carbonaceous grains in the interstellar medium (ISM) within the Radiative Torque (RAT) paradigm. For internal alignment (IA), we find that hydrogenated amorphous carbon (HAC) grains having nuclear paramagnetism due to hydrogen protons have efficient nu...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2023-01-01
|
| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/ace788 |
| _version_ | 1797688667964178432 |
|---|---|
| author | Thiem Hoang Vo Hong Minh Phan Le Ngoc Tram |
| author_facet | Thiem Hoang Vo Hong Minh Phan Le Ngoc Tram |
| author_sort | Thiem Hoang |
| collection | DOAJ |
| description | We study the internal and external alignment of carbonaceous grains in the interstellar medium (ISM) within the Radiative Torque (RAT) paradigm. For internal alignment (IA), we find that hydrogenated amorphous carbon (HAC) grains having nuclear paramagnetism due to hydrogen protons have efficient nuclear relaxation, whereas both HAC and graphite grains can have efficient inelastic relaxation at both low- J and high- J attractors. For external alignment, HAC and pure graphite grains can align with the radiation direction ( k -RAT) at low- J attractors but cannot have stable alignment at high- J attractors due to the suppression of radiative precession. However, HAC grains can align with the magnetic field ( B -RAT) at high- J attractors due to fast Larmor precession compared to gas collisions. For HAC grains drifting through the ISM, they can align along the induced electric field ( E -RAT) at low- J attractors due to the fast electric precession and only small HAC grains can align at high- J attractors. Nuclear paramagnetic relaxation is inefficient for HAC due to the suppression of nuclear susceptibility. We then study the alignment of carbon dust in the envelope of a C-rich Asymptotic Giant Branch star (IRC+10216) and find that grains aligned at low- J attractors may occur via k -RAT with the wrong IA in the inner region but via B -RAT in the outer region. However, grains aligned at high- J attractors have the right IA alignment via k -RAT due to efficient inelastic relaxation. The polarization pattern observed toward IRC+10216 by SOFIA/HAWC+ can be reproduced when only grains at low- J attractors are present due to the removal of grains at high- J attractors by the RAT disruption. |
| first_indexed | 2024-03-12T01:34:01Z |
| format | Article |
| id | doaj.art-3e9a75f1c6664b05ab438bb2ac38ff9d |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-12T01:34:01Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-3e9a75f1c6664b05ab438bb2ac38ff9d2023-09-11T09:20:24ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-01954221610.3847/1538-4357/ace788Internal and External Alignment of Carbonaceous Grains within the Radiative Torque ParadigmThiem Hoang0https://orcid.org/0000-0003-2017-0982Vo Hong Minh Phan1Le Ngoc Tram2Korea Astronomy and Space Science Institute , Daejeon, 34055, Republic of Korea ; thiemhoang@kasi.re.kr; Korea University of Science and Technology , 217 Gajeong-ro, Yuseong-gu, Daejeon, 34113, Republic of KoreaInstitute for Theoretical Particle Physics and Cosmology (TTK), RWTH Aachen University , D-52056 Aachen, Germany ; vhmphan@physik.rwth-aachen.deMax-Planck-Institut für Radioastronomie , Auf dem Hügel 69, D-53121, Bonn, Germany ; nle@mpifr-bonn.mpg.deWe study the internal and external alignment of carbonaceous grains in the interstellar medium (ISM) within the Radiative Torque (RAT) paradigm. For internal alignment (IA), we find that hydrogenated amorphous carbon (HAC) grains having nuclear paramagnetism due to hydrogen protons have efficient nuclear relaxation, whereas both HAC and graphite grains can have efficient inelastic relaxation at both low- J and high- J attractors. For external alignment, HAC and pure graphite grains can align with the radiation direction ( k -RAT) at low- J attractors but cannot have stable alignment at high- J attractors due to the suppression of radiative precession. However, HAC grains can align with the magnetic field ( B -RAT) at high- J attractors due to fast Larmor precession compared to gas collisions. For HAC grains drifting through the ISM, they can align along the induced electric field ( E -RAT) at low- J attractors due to the fast electric precession and only small HAC grains can align at high- J attractors. Nuclear paramagnetic relaxation is inefficient for HAC due to the suppression of nuclear susceptibility. We then study the alignment of carbon dust in the envelope of a C-rich Asymptotic Giant Branch star (IRC+10216) and find that grains aligned at low- J attractors may occur via k -RAT with the wrong IA in the inner region but via B -RAT in the outer region. However, grains aligned at high- J attractors have the right IA alignment via k -RAT due to efficient inelastic relaxation. The polarization pattern observed toward IRC+10216 by SOFIA/HAWC+ can be reproduced when only grains at low- J attractors are present due to the removal of grains at high- J attractors by the RAT disruption.https://doi.org/10.3847/1538-4357/ace788Astrophysical dust processesCircumstellar dustInterstellar dust processesDust compositionStarlight polarizationEvolved stars |
| spellingShingle | Thiem Hoang Vo Hong Minh Phan Le Ngoc Tram Internal and External Alignment of Carbonaceous Grains within the Radiative Torque Paradigm The Astrophysical Journal Astrophysical dust processes Circumstellar dust Interstellar dust processes Dust composition Starlight polarization Evolved stars |
| title | Internal and External Alignment of Carbonaceous Grains within the Radiative Torque Paradigm |
| title_full | Internal and External Alignment of Carbonaceous Grains within the Radiative Torque Paradigm |
| title_fullStr | Internal and External Alignment of Carbonaceous Grains within the Radiative Torque Paradigm |
| title_full_unstemmed | Internal and External Alignment of Carbonaceous Grains within the Radiative Torque Paradigm |
| title_short | Internal and External Alignment of Carbonaceous Grains within the Radiative Torque Paradigm |
| title_sort | internal and external alignment of carbonaceous grains within the radiative torque paradigm |
| topic | Astrophysical dust processes Circumstellar dust Interstellar dust processes Dust composition Starlight polarization Evolved stars |
| url | https://doi.org/10.3847/1538-4357/ace788 |
| work_keys_str_mv | AT thiemhoang internalandexternalalignmentofcarbonaceousgrainswithintheradiativetorqueparadigm AT vohongminhphan internalandexternalalignmentofcarbonaceousgrainswithintheradiativetorqueparadigm AT lengoctram internalandexternalalignmentofcarbonaceousgrainswithintheradiativetorqueparadigm |