Time：2023/04/21 (Fri.) 12:10
Place：
3F R307 Seminar Room, Cosmology Hall, NTU
&
Webex online (Meeting number：2552 311 9786 / Password：TG23 (8423 from phones and video systems))

Title：Thermodynamics coupled to dynamics in the interstellar medium
Speaker：Nai-Chieh Lin (NTNU)
Abstract：
In this study, we investigate the impact of cooling and heating processes on the thermodynamics and dynamics of the cold interstellar medium (ISM). The widely accepted polytropic equation of state describes the relationship between temperature and density of the cold ISM in star-forming molecular clouds, with a polytropic index of γ ∼ 0.7 when n < 10^4 and γ ∼ 1 when n > 10^4. However, there are discrepancies between observational results and theoretical predictions that assume that the heating or cooling timescales are smaller than the dynamical timescale and do not account for the work done by compression or expansion. To address this issue, we use the adaptive mesh refinement (AMR) code RAMSES to conduct numerical simulations and determine the effective polytropic index. Our simulations adopt the atomic-molecular cooling function and parametric cooling function. The results suggest that when studying the primordial cold ISM, the work done by dynamical processes should be included in the theoretical model since cooling is not efficient in low metallicity scenarios. Overall, our study highlights the need for a more comprehensive understanding of the dynamics and thermodynamics of the cold ISM and the importance of considering the effects of cooling and heating processes on these systems.

Title：Hear the Wind Sing: Distinguishing MHD Disk Winds from Turbulent Viscosity through Substructure Morphology in Planet-forming Disks
Speaker：Yin-Hao Wu (University of Leicester)
Abstract：
The traditional paradigm of viscosity-dominated evolution of protoplanetary discs has been recently challenged by magnetized disc winds. However, distinguishing wind-driven and turbulence-driven accretion through observations has been difficult. In this study, we present a novel approach to identifying their separate contribution to angular momentum transport by studying the gap and ring morphology of planet-forming discs in the ALMA continuum. We model the gap-opening process of planets in discs with both viscous evolution and wind-driven accretion by 2D multi-fluid hydrodynamical simulations. Our results show that gap-opening planets in wind-driven accreting discs generate unique substructures that differ from those in purely viscous discs. Specifically, we demonstrate that discs, where wind-driven accretion dominates the production of substructures, exhibit significant asymmetries. Based on the diverse outputs of mock images in the ALMA continuum, we roughly divide the planet-induced features into four regimes (moderate-viscosity dominated, moderate-wind dominated, strong-viscosity dominated, inviscid). The classification of these regimes sets up a potential method to constrain the strength of magnetized disc wind and viscosity based on the observed gap and ring morphology. We discuss the asymmetry feature in our mock images and its potential manifestation in ALMA observations.