BEGIN:VCALENDAR VERSION:2.0 PRODID:-//wp-events-plugin.com//7.2.3.1//EN TZID:Europe/Paris X-WR-TIMEZONE:Europe/Paris BEGIN:VEVENT UID:123@atst.osups.universite-paris-saclay.fr DTSTART;TZID=Europe/Paris:20251209T093000 DTEND;TZID=Europe/Paris:20251209T123000 DTSTAMP:20251201T222808Z URL:https://atst.osups.universite-paris-saclay.fr/calendrier/phd-defense-s limane-mzerguat/ SUMMARY:PhD defense: Slimane Mzerguat DESCRIPTION:I am pleased to invite you to my PhD defense\, which will take place on Tuesday\, 9 December 2025 at 09:30 at Institut d’Astrophysique Spatiale (IAS)\, Bâtiment 121\, Université Paris-Saclay\, Orsay.\nThe de fense will also be streamed live on YouTube. After the defense\, a light r eception will be offered. If you plan to join\, please fill out this short two-question form.\nThesis title:\n“Evolution of transient structures i n the solar corona and of their composition: a multi-instrument study with Solar Orbiter”\nSupervisors:\n\n Éric Buchlin (IAS\, Université Pari s-Saclay)\n Miho Janvier (IAS\, Université Paris-Saclay / ESA)\n\nJury:\ n\n Laurent Verstraete — Professor\, Université Paris-Saclay (IAS) — President\n Louise Harra — Professor\, ETH Zürich (PMOD/WRC) — Revi ewer\n Étienne Pariat — CNRS Research Scientist (French-Spanish Labora tory for Astrophysics in Canarias) — Reviewer\n David Brooks — Profes sor\, George Mason University / MSSL–UCL / JAXA — Examiner\n Alessand ra Giunta — Associate Professor\, Università di Catania — Examiner\n\ nAbstract:\nPlasma composition is a powerful diagnostic for understanding the solar corona and for linking remote observations to in-situ solar-wind measurements. Above the transition region\, elemental abundances differ f rom photospheric values due to the First Ionization Potential (FIP) effect : low-FIP elements (FIP <\; 10 eV) are typically enhanced by factors of ∼3–4 in the corona and solar wind\, while high-FIP elements remain nea r photospheric levels.\n\nA proposed explanation for this bias is the pond eromotive force\, which arises near the top of the chromosphere as a resul t of gradients in Alfvén-wave energy density. This thesis focuses on mid- FIP elements (FIP ≈ 10 eV)\, especially sulfur (10.36 eV)\, whose fracti onation can mimic low- or high-FIP behavior depending on magnetic topology and the depth of wave penetration into the chromosphere.\n\nUsing space-b orne spectroscopy with Solar Orbiter/SPICE\, I perform one of the first re mote-sensing measurements of the sulfur FIP bias across distinct solar str uctures and compare the results with predictions of the ponderomotive-forc e model. To enable this\, I developed SAFFRON\, an open-source Python tool tailored for SPICE Level-2 data that provides cosmic-ray removal\, adapti ve binning\, constrained multi-Gaussian fitting\, uncertainty propagation\ , and computation of FIP-bias maps.\n\nApplied to coronal-hole plumes (bri ght\, open structures rooted in coronal holes and contributing to the fast wind)\, sulfur enrichment is measured in the transition region at plume f ootpoints\, consistent with models where plume formation facilitates mid-F IP fractionation. In active regions\, however\, sulfur diagnostics become density-sensitive around ∼0.1 MK\, increasing uncertainties. I quantify this effect and outline strategies\, incorporating independent density con straints\, to retrieve reliable composition in dense environments.\n\nToge ther\, these results improve our understanding of coronal composition vari ability and establish mid-FIP diagnostics as indicators of transition-regi on activity and chromospheric Alfvén waves. The upcoming high-latitude ph ases of Solar Orbiter will be essential to extend this work to polar coron al holes. Coordinated multi-instrument campaigns combining ground-based sp ectropolarimetry (e.g.\, DKIST\, GST) with EUV spectroscopy (SPICE\, Hinod e/EIS\, Solar-C/EUVST) will further constrain the physical processes that shape elemental fractionation in the solar atmosphere.\n\n(Transmis par Sl imane Mzerguat) CATEGORIES:Séminaires et soutenances de thèse/HDR LOCATION:Institut d'Astrophysique Spatiale - CNRS - Université Paris-Sacla y\, Rue Jean-Dominique Cassini\, Bures-sur-Yvette\, 91440\, France X-APPLE-STRUCTURED-LOCATION;VALUE=URI;X-ADDRESS=Rue Jean-Dominique Cassini\ , Bures-sur-Yvette\, 91440\, France;X-APPLE-RADIUS=100;X-TITLE=Institut d' Astrophysique Spatiale - CNRS - Université Paris-Saclay:geo:0,0 END:VEVENT BEGIN:VTIMEZONE TZID:Europe/Paris X-LIC-LOCATION:Europe/Paris BEGIN:STANDARD DTSTART:20251026T020000 TZOFFSETFROM:+0200 TZOFFSETTO:+0100 TZNAME:CET END:STANDARD END:VTIMEZONE END:VCALENDAR