Emission from Hot Gas in Pre-Main Sequence Objects: The Accretion Shock and the Inner Disk.

High energy (X-ray and ultraviolet) emission traces hot gas produced by energetic phenomena in T Tauri stars. These phenomena include magnetic heating of the stellar atmosphere and magnetospheric accretion of disk gas onto the stellar surface. High energy emission irradiates the planet-forming disk during a key time for the origin of planets, so an understanding of these energetic processes and their evolution is crucial for theories of disk evolution and planet formation In this thesis, I analyze X-ray and ultraviolet observations of young stars to study high energy events and follow their evolution. I confirm that X-ray emission is saturated during the T Tauri phase and suggest that far ultraviolet emission is also saturated at this age, possibly because the same mechanism heats both the chromosphere and corona. I compare accretion diagnostics for a large sample of T Tauri stars to characterize the properties of magnetospheric accretion. For the first time, I use models of the accretion emission which have contributions from multiple accretion hot spots, characterized by varying energy fluxes in the accretion columns. Models of T Tauri magnetospheres and the magnetic footprints on the star physically motivate this multi-component description of accretion. For RECX-11, a source near the final stage of disk depletion, I show that it has a very low mass accretion rate. If theories that predict the circumstellar disk is losing mass at very high rates are correct, the disk of RECX-11 would have a gap or hole in it, which it does not. I also present observations of hot H2 gas in the inner circumstellar disk. I find that the strength of the H2 emission is correlated with the accretion luminosity of the T Tauri star and show that for young stars in which accretion has ceased, there is no H2 left in the inner disk. I show this is true even for non-accreting young stars at 1-3 Myr, indicating rapid disk removal. Observations of circumstellar gas, combined with knowledge of the radiation fields, are crucial for studying disk evolution. Here, I provide timescales for gas depletion and constraints to disk dissipation models.PHDAstronomy and AstrophysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/96153/1/lingleby_1.pd

Adopting an ethical approach to migration health policy, practice and research

Migration health is affected by decision making at levels ranging from global to local, both within and beyond the health sector. These decisions impact seeking, entitlements, service delivery, policy making and knowledge production on migration health. It is key that ethical challenges faced by decision makers are recognised and addressed in research and data, clinical practice and policy making on migration health. An ethical approach can provide methods to identify ethical issues, frameworks for systematising information and suggesting ethically acceptable solutions, and guidance on procedural concerns and legitimate decision making processes. By unpacking dilemmas, conflicts of interests and values at stake, an ethical approach is relevant for all who make decisions about migration health policy and practice. Adopting an ethical approach to migration health benefits governments, organisations, policy makers, health workers, data managers, researchers and migrants themselves. First, it highlights the inherent normative questions and trade-offs at stake in migration health. Second, it assists decision makers in deciding what is the ethically justifiable thing to do through an ‘all things considered’ approach. Third, ethical frameworks and technical guidance set normative and practical standards for decision makers facing ethical questions – from ‘bedside rationing’ to collection of big data or in policy making – that can ensure that migrants’ interests are considered. Fourth, there is a need for greater transparency and accountability in decision making, as well as meaningful participation of migrant groups. An ethical approach connects to public health, economic and human rights arguments and highlights the urgent need to mainstream concerns for migrants in global and national health responses