Séminaire IPAG

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Massive Stars near Solar System’s Parent Molecular Cloud Affected the Composition of Its Building Blocks

jeudi 3 février 2022 - 11h00

Lionel Vacher - IPAG
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Primitive meteorites display mass-independent oxygen isotope anomalies (∆17O) that were likely caused by ultraviolet (UV) photochemistry of gas-phase molecules. CO self-shielding is proposed to explain the Solar System’s ∆17O variability and may have occurred either (1) in the outer solar nebula by light from the young Sun or (2) in the parent molecular cloud by light from nearby massive stars. However, direct constraints on the astrophysical source responsible for photochemical processing are not possible with oxygen isotopes alone because a large range of ∆17O values can be generated by this process. Sulfur isotopes may have also experienced mass-independent isotope fractionation (∆33S & ∆36S) by UV photolysis in the solar nebula or molecular cloud. Photolysis experiments of H2S at the Lyman−alpha spectral line (121.6 nm) and larger or smaller wavelengths produce mass-independent anomalies that define distinct ∆36S/∆33S ratios. Young stars have strong emission at Lyman−alpha, while massive O and B stars dominate the interstellar UV flux. Thus, the photodissociation of H2S can serve to differentiate between massive stars and young T-Tauri stars as the astronomical source of isotope-selective photodissociation. Analysis of paired oxygen and sulfur isotope systematics in cosmic symplectite (a nm-scale intergrowth of magnetite with high ∆17O values and pentlandite) in the primitive carbonaceous chondrite Acfer 094 can provide unique insights into the astrophysical environment for the Solar System formation.

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Hôtes : Pierre Beck

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