Dr. Shridharan Baskaran (Tata Institute, Mumbai, India.)
28 May 2025
11:30, Aula Piazzi
Abstract:
In this talk, I will present our comprehensive analysis of ~80 JWST/MIRI archival spectra of Class II protoplanetary disks, with a focus on mid-infrared (MIR) hydrogen emission lines arising from transitions with upper levels N = 6–14. The balance between accretion and ejection plays a fundamental role in regulating disk dispersal and ultimately determines the mass reservoir available for planet formation. While traditional accretion diagnostics using optical and near-infrared hydrogen lines often suffer from high extinction and contamination by winds or jets, I will show how MIR HI lines, thanks to MIRI’s broad wavelength coverage (5–28 µm) and high sensitivity, offer a powerful alternative. I will discuss our identification of specific MIR HI lines that serve as reliable tracers of accretion, the molecular contamination affecting them, and the methods we developed to mitigate this issue. I will also introduce new empirical calibrations to convert MIR HI line luminosities into accretion luminosities, enabling direct accretion rate estimates from JWST/MIRI spectra—even in highly embedded YSOs. By incorporating the Kwan & Fischer (2011) models, I will demonstrate how MIR HI lines can constrain the physical properties of accretion columns with improved fidelity. Finally, I will highlight how we connect mass accretion and ejection rates using fine-structure lines such as [Ne II], [Fe II], and [Ar II], aiming to provide a more complete picture of disk evolution and the initial conditions for planet formation in Class II systems.