RSAA Colloquia / Seminars / Feast-of-Facts: Tuesday, 29 January 2019, 11:00-12:00; CSO Common Room

Christopher Nolan

"Understanding protostellar jet feedback on disk and cloud scales (End-of-Thesis colloquium)"

Feedback in the form of protostellar jets plays an important role in the process of star formation. These jets are launched from protostellar disks at au scales via the interaction of magnetic fields with weakly ionised disk material, and extend up to cloud scales (~ 1-3 pc), driving turbulence and influencing the star formation rate and the initial mass function. In this talk, I present the results of my PhD work on jet feedback, divided into two parts. In part one, I present a novel approach to modelling the jet-launching region in protostellar disks, combining a series of 1.5D semi-analytic, steady-state, vertical disc-wind solutions into a radially extended 1+1.5D model, incorporating all three magnetic diffusion mechanisms (Ohm, Hall and ambipolar). From this model I find that the majority of mass outflow via disc winds occurs over a radial width of a fraction of an au, with outflow rates attenuating rapidly on either side. I also find that the mass accretion rate, midplane plasma beta, surface density profile and ionisation structure each have significant effects on both the location of the wind-launching region and the ejection/accretion ratio. In part two, I present new results characterising the density variance - Mach number relation in interstellar medium (ISM) turbulence. This relation is important for understanding the properties of ISM turbulence driven by feedback processes, including the star formation rate and initial mass function, and is well-studied in the isothermal regime. I extend the analysis to the adiabatic regime, modelling turbulence with diatomic molecular (gamma = 7/5) and monatomic (gamma = 5/3) adiabatic indices. Stirring the gas solenoidally at low wavenumbers, I find that as the gas heats in adiabatic compressions, it evolves along the relationship in the density variance-Mach number plane, but deviates significantly from the isothermal form. I calculate new relations that take the adiabatic index into account and provide good fits for a range of Mach numbers.