Séminaire/Seminar Galaxies |
| « Ejecta Velocities and Decline Rates in Type Ia Supernovae: The Role of High-Velocity Features » |
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Artur Hakobyan |
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Type Ia supernovae (SNe Ia) exhibit diverse spectroscopic and photometric behaviours that encode critical information about their explosion physics and progenitor systems. I will begin the talk with a concise introduction to the key spectral and light-curve properties of SNe Ia, followed by an overview of the principal explosion models and their observational diagnostics. I will then present results from our recent analysis of a sample of 145 nearby SNe Ia observed near maximum light, focusing on the Si II ?6355 and Ca II IR3 absorption features.
We show that the velocity distribution of the Ca II photospheric-velocity feature (PVF) is unimodal, in contrast to the well-established bimodal Si II PVF distribution that separates high-velocity and normal-velocity subclasses of SNe Ia. This distinction likely reflects subclass-dependent line-formation depths and excitation conditions. High-velocity features (HVFs) - broad, blueshifted absorptions formed in rapidly expanding outer ejecta or in material interacting with circumstellar gas - play an important role in shaping early-time spectra. We further demonstrate that a strong correlation between Si II PVF velocity and light-curve decline rate emerges only in HVF-weak SNe Ia. This behaviour is consistent with more energetic, slow-declining explosions producing faster ejecta, whereas HVF-strong events show no such trend, likely due to circumstellar interaction that modulates their apparent velocity structure. These findings provide new constraints on SN Ia ejecta kinematics, subclass diversity, and the physical origins of their spectroscopic velocity features. |
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Thursday 27 November 2025 - 11:30 Salle Entresol Daniel Chalonge Institut d'Astrophysique de Paris |
| Page web du séminaire / Seminar's webpage |