Light scattering experiments have been carried out at visible light for two kinds <">

Characterizing cometary dust grains with polarimetry

crossref(2022)

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<p><span dir="ltr" role="presentation">Light scattering experiments have been carried out at visible light for two kinds </span><span dir="ltr" role="presentation">of dust samples: narrow size distributions consisting of low-absorbing particles </span><span dir="ltr" role="presentation">with sizes in the micron domain, plus millimeter-sized single grains. The polari</span><span dir="ltr" role="presentation">metric analysis of the scattered light has revealed as a very precise tool for size </span><span dir="ltr" role="presentation">characterization of the samples of particles in the resonance regime, while it let </span><span dir="ltr" role="presentation">us distinguish the compact/fluffy structure feature of particles much larger than </span><span dir="ltr" role="presentation">the wavelength.</span></p> <p><span dir="ltr" role="presentation">First, four narrow size distributions of forsterite particles, spanning a broad </span><span dir="ltr" role="presentation">range of scattering sizes in the resonance regime, were measured. Forsterite is </span><span dir="ltr" role="presentation">a Mg-rich olivine representative of low-absorbing cosmic dust particles that has </span><span dir="ltr" role="presentation">been identified in several comets, e.g. 1P/Halley, Hale&#8211;Bopp, 9P/Tempel and </span><span dir="ltr" role="presentation">81P/Wild2 (see [1] and references therein). The maximum of the degree of lin</span><span dir="ltr" role="presentation">ear polarization (DLP) decreases with the size of the particles. That maximum </span><span dir="ltr" role="presentation">occurs around 90</span><span dir="ltr" role="presentation">&#186;</span> <span dir="ltr" role="presentation">in all cases, but the angle ranges from 75</span><span dir="ltr" role="presentation">&#186;</span> <span dir="ltr" role="presentation">to 140</span><span dir="ltr" role="presentation">&#186;</span><span dir="ltr" role="presentation">, increasing </span><span dir="ltr" role="presentation">with the grain size [2]. Furthermore, dust particles with size parameters from </span><span dir="ltr" role="presentation">&#8764;</span> <span dir="ltr" role="presentation">6 to</span> <span dir="ltr" role="presentation">&#8764;</span> <span dir="ltr" role="presentation">20 seem to be responsible for the negative polarization branch (NBP). </span><span dir="ltr" role="presentation">This is in agreement with the idea that the NBP might be caused by coherent </span><span dir="ltr" role="presentation">back-scattering by wavelength-scaled features of the grains (see .e.g. [3]).</span></p> <p><br role="presentation" /><span dir="ltr" role="presentation">On the other hand, millimeter-sized particles were identified to reproduce </span><span dir="ltr" role="presentation">the flux curve of Fomalhaut protoplanetary disk [4]. Light scattering was then</span><br role="presentation" /><span dir="ltr" role="presentation">measured for the same kind of grains in an attempt to reproduce the comet </span><span dir="ltr" role="presentation">67P/Churyumov-Gerasimenko phase function obtained</span> <span dir="ltr" role="presentation">in situ</span> <span dir="ltr" role="presentation">by the OSIRIS</span><br role="presentation" /><span dir="ltr" role="presentation">camera system onboard the ESA Rosetta mission. In that case it was found that </span><span dir="ltr" role="presentation">large porous particles with organic inclusions can reproduce both, ground-based </span><span dir="ltr" role="presentation">observations of the DLP and the OSIRIS phase functions [5].</span></p> <p>&#160;</p> <p><strong><span dir="ltr" role="presentation">References</span></strong></p> <p><span dir="ltr" role="presentation">1. Frattin, E., Mu&#241;</span><span dir="ltr" role="presentation">oz, O., Moreno, F., Nava, J., Escobar-Cerezo, J., Gomez Martin, J.C., </span><span dir="ltr" role="presentation">Guirado, D., Cellino, A., Coll, P., Raulin, F., Bertini, I., Cremonese, G., Lazzarin, </span><span dir="ltr" role="presentation">M., Naletto, G., Forgia, F.L.: Experimental phase function and degree of linear </span><span dir="ltr" role="presentation">polarization of cometary dust analogues. Monthly Notices of the Royal Astronomical </span><span dir="ltr" role="presentation">Society</span> <span dir="ltr" role="presentation">484</span><span dir="ltr" role="presentation">, 2198&#8211;2211 (2019)</span></p> <p><span dir="ltr" role="presentation">2. Mu&#241;</span><span dir="ltr" role="presentation">oz, O., Frattin, E., Jardiel, T., G&#243;</span><span dir="ltr" role="presentation">mez-Mart&#237;</span><span dir="ltr" role="presentation">n, J.C., Moreno, F., Ramos, J.L., </span><span dir="ltr" role="presentation">Guirado, D., Peiteado, M., Caballero, A.C., Milli, J., M&#233;</span><span dir="ltr" role="presentation">nard, F.: Retrieving dust </span><span dir="ltr" role="presentation">grain sizes from photopolarimetry: An experimental approach. The Astrophysical </span><span dir="ltr" role="presentation">Journal Supplement Series</span> <span dir="ltr" role="presentation">256</span><span dir="ltr" role="presentation">(17 (12pp)) (2021)</span></p> <p><span dir="ltr" role="presentation">3. Muinonena, K., Penttil&#228;, A., Videen, G.: Polarimetry of Stars and Planetary Systems, chap. Multiple Scattering of Light in Particulate Planetary Media. Cambridge University Press, Cambridge (2015)</span></p> <p><span dir="ltr" role="presentation">4. Mu&#241;oz, O., Moreno, F., Vargas-Mart&#237;n, F., Guirado, D., Escobar-Cerezo, J., Min, M., Hovenier, J.W.: Experimental phase functions of millimeter-sized cosmic dust grains. The Astrophysical Journal 846(85 (8pp)) (2017)</span></p> <p><span dir="ltr" role="presentation">5. Mu&#241;</span><span dir="ltr" role="presentation">oz, O., Moreno, F., G&#243;</span><span dir="ltr" role="presentation">mez-Mart&#237;</span><span dir="ltr" role="presentation">n, J.C., Vargas-Mart&#237;</span><span dir="ltr" role="presentation">n, F., Guirado, D., </span><span dir="ltr" role="presentation">Ramos, J.L., Bustamante, I., Bertini, I., Frattin, E., Markannen, J., Tubiana, C., </span><span dir="ltr" role="presentation">Fulle, M., G&#252;</span><span dir="ltr" role="presentation">ttler, C., Sierks, H., Rotundi, A., Corte, V.D., Ivanovski, S., Za</span><span dir="ltr" role="presentation">kharov, V.V., Bockel&#233;</span><span dir="ltr" role="presentation">e-Morvan, D., Blum, J., Merouane, S., Levasseur-Regourd, </span><span dir="ltr" role="presentation">A.C., Kolokolova, L., Jardiel, T., Caballero, A.C.: Experimental phase function and </span><span dir="ltr" role="presentation">degree of linear polarization curves of millimetersized cosmic dust analogs. The </span><span dir="ltr" role="presentation">Astrophysical Journal Supplement Series</span> <span dir="ltr" role="presentation">247</span><span dir="ltr" role="presentation">(19 (13pp)) (2020)</span></p>
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