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Binary systems containing one or two white dwarfs are important for studying stellar evolution and interactions under a wide range of astrophysical conditions. Thanks to the Gaia mission we have identified the first statistically significant and unbiased sample of ~ 170 000 white dwarf binary candidates. It comprises both systems that never interacted that are part of common proper motion pairs and systems that evolved through mass transfer episodes resulting in close white dwarf binaries. White dwarf binaries hold the potential to observationally constrain a wide variety of key ingredients that currently limit the validity of theoretical models., Published in The Messenger vol. 190, pp. 4-6, March 2023.

]Context] Kinematic and chemical tagging of stellar populations have both revealed much information on the past and recent history of the Milky Way, including its formation history, merger events, and mixing of populations across the Galactic disk and halo. [Aims] We present the first detailed 3D kinematic analysis of a sample of 3133 white dwarfs that used Gaia astrometry plus radial velocities, which were measured either by Gaia or by ground-based spectroscopic observations. The sample includes either isolated white dwarfs that have direct radial velocity measurements, or white dwarfs that belong to common proper motion pairs that contain nondegenerate companions with available radial velocities. A subset of common proper motion pairs also have metal abundances that have been measured by large-scale spectroscopic surveys or by our own follow-up observations. [Methods] We used the white dwarfs as astrophysical clocks by determining their masses and total ages through interpolation with dedicated evolutionary models. We also used the nondegenerate companions in common proper motions to chemically tag the population. Combining accurate radial velocities with Gaia astrometry and proper motions, we derived the velocity components of our sample in the Galactic rest frame and their Galactic orbital parameters. [Results] The sample is mostly located within ∼300 pc from the Sun. It predominantly contains (90-95%) thin-disk stars with almost circular Galactic orbits, while the remaining 5-10% of stars have more eccentric trajectories and belong to the thick disk. We identified seven isolated white dwarfs and two common proper motion pairs as halo members. We determined the age-velocity dispersion relation for the thin-disk members, which agrees with previous results that were achieved from different white dwarf samples without published radial velocities. The age-velocity dispersion relation shows signatures of dynamical heating and saturation after 4-6 Gyr. We observed a mild anticorrelation between [Fe/H] and the radial component of the average velocity dispersion, showing that dynamical mixing of populations takes place in the Galactic disk, as was detected through the analysis of other samples of FGK stars. [Conclusions] We have shown that a white dwarf sample with accurate 3D kinematics and well-measured chemical compositions enables a wider understanding of their population in the solar neighborhood and its connection with the Galactic chemodynamics. The legacy of existing spectroscopic surveys will be boosted by the availability of upcoming larger samples of white dwarfs and common proper motion pairs with more uniform high-quality data., R.R. has received funding from the postdoctoral fellowship programme Beatriu de Pinós, funded by the Secretary of Universities and Research (Government of Catalonia) and by the Horizon 2020 programme of research and innovation of the European Union under the Maria Skłodowska-Curie grant agreement No 801370. A.R.M. acknowledges additional support from Grant RYC-2016-20254 funded by MCIN/AEI/10.13039/501100011033 and by ESF Investing in your future. S.T. acknowledges support from the MINECO under the AYA2017-86274-P grant, and the AGAUR grant SGR-661/2017. J.M. acknowledges support from the Accordo Attuativo ASI-INAF n. 2018.22.HH.O, Partecipazione alla fase B1 della missione Ariel. M.E.C. acknowledges NASA grants 80NSSC17K0008 and 80NSSC20K0193. P.E.T. and T.C. have received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme n. 677706 (WD3D). U.H. acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG) through grants IR190/1-1, HE1356/70-1, and HE1356/71-1. T.C. was supported by a Leverhulme Trust Grant (ID RPG-2020-366). J.J.R. is thankful for support from NSFC (grant No. 11903048, 11833006).

Practically all known planet hosts will evolve into white dwarfs, and large parts of their planetary systems will survive this transition - the same is true for the solar system beyond the orbit of Mars. Spectroscopy of white dwarfs accreting planetary debris provides the most accurate insight into the bulk composition of exo-planets. Ground-based spectroscopic surveys of ~260, 000 white dwarfs detected with Gaia will identify >1000 evolved planetary systems, and high-throughput high-resolution space-based ultraviolet spectroscopy is essential to measure in detail their abundances. So far, evidence for two planetesimals orbiting closely around white dwarfs has been obtained, and their study provides important constraints on the composition and internal structure of these bodies. Major photometric and spectroscopic efforts will be necessary to assemble a sample of such close-in planetesimals that is sufficiently large to establish their properties as a population, and to deduce the architectures of the outer planetary systems from where they originated. Mid-infrared spectroscopy of the dusty disks will provide detailed mineralogical information of the debris, which, in combination with the elemental abundances measured from the white dwarf spectroscopy, will enable detailed physical modelling of the chemical, thermodynamic, and physical history of the accreted material. Flexible multi-epoch infrared observations are essential to determine the physical nature, and origin of the variability observed in many of the dusty disks. Finally, the direct detection of the outer reservoirs feeding material to the white dwarfs will require sensitive mid- and far-infrared capabilities., 5 pages, 3 figures Science White Paper submitted to the Astro2020 Decadal Survey

This dissertation is made up of three distinct parts: 1) A comprehensive, structured literature review 2) a mixed-methods descriptive study and 3) an inductive thematic qualitative analysis. The objective of this dissertation is to explore the concepts of compassion fatigue, compassion satisfaction and burnout as they relate to the practices of narrative medicine among expatriate humanitarian aid workers. Data collected for this research focuses on expatriate healthcare workers who provided direct patient care during the 2013-2016 Ebola response in Sierra Leone, Liberia and Guinea. Findings from these studies support the growing body of evidence and discussion regarding psychosocial support of healthcare workers in humanitarian contexts. To the extent that global health is public health (Fried, 2010), results from this dissertation will contribute guidance in the understanding and management of aid workers in contexts beyond the Ebola response.