arXiv subjects

J. Lasue

Publications and source records attributed to J. Lasue.

4 recordsLinked to original sources

arXiv2026

The dust in Sauron's eye - Observational and experimental results on the debris disk around HR 4796

The optical properties (scattering phase function SPF; degree of linear polarization DoLP; reflectance) of the dust particles orbiting in debris disks can be retrieved through scattered light imaging and are linked to the physicochemical properties of the dust (size, shape, composition...). Among debris disks, the bright, narrow disk surrounding HR 4796A presents several peculiarities, in particular unusually high DoLP values at small scattering angles. We aim at improving the constraints on the properties of the dust particles orbiting in HR 4796. We use new observational data (SPHERE/ZIMPOL and IRDIS) in scattered light of HR 4796, for lambda = 0.63 um; 0.79 um and 1.25 um. We modeled the disk at each of these wavelengths and found geometric parameters consistent with previous results. We obtained the parametrized SPF and DoLP over the whole range of scattering angles (13 degrees to 167 degrees) and extracted the DoLP and spectral reflectance at 90 degrees (without any parametrization) from the visible to the NIR wavelength range. We compared the reflectance and polarimetric properties of HR 4796 to those measured on a laboratory dust sample and find that the sample providing the best match appears to be large iron sulfides particles. We confirm that the DoLP of HR 4796 peaks at high values (> 45 percent) and for small scattering angles (< 55 degrees). At a 90 degrees scattering angle, we observe a red spectral slope in the visible and NIR wavelength range, as well as a blue polarimetric slope. These results are compatible with large (a few um to 100 um) absorbents being the main scatterers in the disk. We show that the DoLP of HR 4796 is notably different from that of Solar System comets and seems closer to that of some more processed near-Earth orbit asteroids, possibly indicating devolatilization and/or melting induced by space weathering on the dust particles of HR 4796.

astro-ph.EP↗

arXiv2023

Cometary dust collected by MIDAS on board Rosetta II. Particle shape descriptors and pristineness evaluation

The MIDAS (Micro-Imaging Dust Analysis System) atomic force microscope on board the Rosetta comet orbiter investigated and measured the 3D topography of a few hundred nm to tens of $μ$m sized dust particles of 67P/Churyumov-Gerasimenko with resolutions down to a few nanometers, giving insights into the physical processes of our early Solar System. We analyze the shapes of the cometary dust particles collected by MIDAS on the basis of a recently updated particle catalog with the aim to determine which structural properties remained pristine. We develop a set of shape descriptors and metrics such as aspect ratio, elongation, circularity, convexity, and particle surface/volume distribution, which can be used to describe the distribution of particle shapes. Furthermore, we compare the structure of the MIDAS dust particles and the clusters in which the particles were deposited to those found in previous laboratory experiments and by Rosetta/COSIMA. Finally, we combine our findings to calculate a pristineness score for MIDAS particles and determine the most pristine particles and their properties. We find that the morphological properties of all cometary dust particles at the micrometer scale are surprisingly homogeneous despite originating from diverse cometary environments (e.g., different collection targets that are associated with cometary activities/source regions and collection velocities/periods). We next find that the types of clusters found by MIDAS show good agreement with those defined by previous laboratory experiments, however, there are some differences to those found by Rosetta/COSIMA. Based on our result, we rate 19 out of 1082 MIDAS particles at least moderately pristine, i.e., they are not substantially flattened by impact, not fragmented, and/or not part of a fragmentation cluster.

astro-ph.EP↗

arXiv2019

Synthesis of the Morphological Description of Cometary Dust at Comet 67P

Before Rosetta, the space missions Giotto and Stardust shaped our view on cometary dust, supported by plentiful data from Earth based observations and interplanetary dust particles collected in the Earth's atmosphere. The Rosetta mission at comet 67P/Churyumov-Gerasimenko was equipped with a multitude of instruments designed to study cometary dust. While an abundant amount of data was presented in several individual papers, many focused on a dedicated measurement or topic. Different instruments, methods, and data sources provide different measurement parameters and potentially introduce different biases. This can be an advantage if the complementary aspect of such a complex data set can be exploited. However, it also poses a challenge in the comparison of results in the first place. The aim of this work therefore is to summarise dust results from Rosetta and before. We establish a simple classification as a common framework for inter-comparison. This classification is based on a dust particle's structure, porosity, and strength as well as its size. Depending on the instrumentation, these are not direct measurement parameters but we chose them as they were the most reliable to derive our model. The proposed classification already proved helpful in the Rosetta dust community and we propose to take it into consideration also beyond. In this manner we hope to better identify synergies between different instruments and methods in the future.

astro-ph.EP↗

arXiv2017

The 67P/Churyumov-Gerasimenko observation campaign in support of the Rosetta mission

We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov-Gerasimenko from before Rosetta's arrival until nearly the end of mission in September 2016. These provided essential data for mission planning, large-scale context information for the coma and tails beyond the spacecraft, and a way to directly compare 67P with other comets. The observations revealed 67P to be a relatively `well behaved' comet, typical of Jupiter family comets and with activity patterns that repeat from orbit-to-orbit. Comparison between this large collection of telescopic observations and the in situ results from Rosetta will allow us to better understand comet coma chemistry and structure. This work is just beginning as the mission ends -- in this paper we present a summary of the ground-based observations and early results, and point to many questions that will be addressed in future studies.

astro-ph.EP↗