Sensitivity of Polarization to Grain Shape. I. Convex Shapes
Aligned interstellar grains produce polarized extinction (observed at wavelengths from the far-ultraviolet to the mid-infrared) and polarized thermal emission (observed at far-infrared and submm wavelengths). The grains must be quite nonspherical, but the actual shapes are unknown. The relative effi...
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| Format: | Article |
| Language: | English |
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IOP Publishing
2024-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ad0463 |
| _version_ | 1797353397089730560 |
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| author | B. T. Draine |
| author_facet | B. T. Draine |
| author_sort | B. T. Draine |
| collection | DOAJ |
| description | Aligned interstellar grains produce polarized extinction (observed at wavelengths from the far-ultraviolet to the mid-infrared) and polarized thermal emission (observed at far-infrared and submm wavelengths). The grains must be quite nonspherical, but the actual shapes are unknown. The relative efficacy for aligned grains to produce polarization at optical versus infrared wavelengths depends on particle shape. The discrete dipole approximation is used to calculate polarization cross sections for 20 different convex shapes, for wavelengths from 0.1 to 100 μ m, and grain sizes a _eff from 0.05 to 0.3 μ m. Spheroids, cylinders, square prisms, and triaxial ellipsoids are considered. Minimum aspect ratios required by the observed starlight polarization are determined. Some shapes can also be ruled out because they provide too little or too much polarization at far-infrared and submm wavelengths. The ratio of 10 μ m polarization to integrated optical polarization is almost independent of grain shape, varying by only ±8% among the viable convex shapes; thus, at least for convex grains, uncertainties in grain shape cannot account for the discrepancy between predicted and observed 10 μ m polarization toward Cyg OB2-12. |
| first_indexed | 2024-03-08T13:30:32Z |
| format | Article |
| id | doaj.art-95c30f8a410943babfd74aeaeaf3536d |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-08T13:30:32Z |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-95c30f8a410943babfd74aeaeaf3536d2024-01-17T09:46:56ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-01961110310.3847/1538-4357/ad0463Sensitivity of Polarization to Grain Shape. I. Convex ShapesB. T. Draine0https://orcid.org/0000-0002-0846-936XDept. of Astrophysical Sciences, Princeton University , Princeton, NJ 08544, USA ; draine@astro.princeton.eduAligned interstellar grains produce polarized extinction (observed at wavelengths from the far-ultraviolet to the mid-infrared) and polarized thermal emission (observed at far-infrared and submm wavelengths). The grains must be quite nonspherical, but the actual shapes are unknown. The relative efficacy for aligned grains to produce polarization at optical versus infrared wavelengths depends on particle shape. The discrete dipole approximation is used to calculate polarization cross sections for 20 different convex shapes, for wavelengths from 0.1 to 100 μ m, and grain sizes a _eff from 0.05 to 0.3 μ m. Spheroids, cylinders, square prisms, and triaxial ellipsoids are considered. Minimum aspect ratios required by the observed starlight polarization are determined. Some shapes can also be ruled out because they provide too little or too much polarization at far-infrared and submm wavelengths. The ratio of 10 μ m polarization to integrated optical polarization is almost independent of grain shape, varying by only ±8% among the viable convex shapes; thus, at least for convex grains, uncertainties in grain shape cannot account for the discrepancy between predicted and observed 10 μ m polarization toward Cyg OB2-12.https://doi.org/10.3847/1538-4357/ad0463PolarimetrySpectropolarimetryDust physicsInterstellar dustRadiative transfer |
| spellingShingle | B. T. Draine Sensitivity of Polarization to Grain Shape. I. Convex Shapes The Astrophysical Journal Polarimetry Spectropolarimetry Dust physics Interstellar dust Radiative transfer |
| title | Sensitivity of Polarization to Grain Shape. I. Convex Shapes |
| title_full | Sensitivity of Polarization to Grain Shape. I. Convex Shapes |
| title_fullStr | Sensitivity of Polarization to Grain Shape. I. Convex Shapes |
| title_full_unstemmed | Sensitivity of Polarization to Grain Shape. I. Convex Shapes |
| title_short | Sensitivity of Polarization to Grain Shape. I. Convex Shapes |
| title_sort | sensitivity of polarization to grain shape i convex shapes |
| topic | Polarimetry Spectropolarimetry Dust physics Interstellar dust Radiative transfer |
| url | https://doi.org/10.3847/1538-4357/ad0463 |
| work_keys_str_mv | AT btdraine sensitivityofpolarizationtograinshapeiconvexshapes |