Letters of Intent received in 2017

LoI 2019-1993
White dwarfs as probes of fundamental physics and tracers of planetary, stellar and galactic evolution

Topics

Fundamental physics from observations of white dwarfs

White dwarf mass radius relation and degenerate matter

White dwarfs in binaries and Type 1a supernovae

Composition of extrasolar planetary debris

Circumstellar material and structure of the local ISM

End points of stellar evolution

Atomic physics in the laboratory and in white dwarf atmospheres

Rationale

White dwarfs are the most numerous members of the stellar graveyard. Over 90 percent of all stars currently on the main sequence will end their lives as white dwarfs. As such, they are important laboratories for fundamental studies of stellar evolutionary processes, the evolution and history of the Milky Way Galaxy, the evolution of planetary systems, and the behavior of matter at extreme temperatures and densities. Surveys such as SDSS and SPY (or name your survey here) have given us access to unprecedented white dwarf population. Recent studies incorporating these data bases have initiated a revolution in our understanding of the global properties of this white dwarf population that will continue to grow with the upcoming Gaia and LSST results. For example, consider white dwarf evolution. Once a white dwarf is formed, its evolution is dominated by cooling. As they cool over timescales of billions of years, determinations of the age of the oldest (coolest) white dwarfs place limits on the ages of the components of the Galaxy, such as the thin and thick disks, and the system of open and globular clusters. The detailed temperature distribution of the white dwarf population contains information about the star formation history of the Galaxy. White dwarfs are also extremely important indicators for cosmology. Type Ia supernovae are the standard candles indicating the acceleration of cosmic expansion. However, although it is crucial to identify the progenitor systems, the evolutionary paths leading to these explosions are still poorly understood. Recent surveys have begun to reveal the properties of single and double degenerate progenitors, but the picture is still very unclear and more work is needed. In the past few years, white dwarfs have also begun influence our understanding of the evolution of planetary systems. We have strong evidence that some white dwarfs harbor planetary systems. In a very exciting development, we now know that white dwarfs can disrupt minor planetary bodies and the resulting debris is accreted onto the white dwarf. White dwarfs have a unique photospheric characteristic. The high surface gravity (log g ~ 8) naturally leads to chemically pure hydrogen or helium photospheres. This means that the spectral features produced by the accreted material are not contaminated by original photospheric abundances. The observed features provide a unique opportunity to study the bulk composition of extrasolar planetary material. A subset of accreting white dwarfs contain spectral features of highly ionized heavy elements. Accurate measurements of observed wavelengths can be compared with laboratory measurements to probe the possible variation of the fine structure constant in a strong gravitational field.

White dwarf research is fascinating in its own right, since it requires developments in atomic data and the study of properties of matter under extreme conditions. However, the impact that these studies have on other areas of astrophysics are also enormous. Thus, the time is ripe to bring together experts from different branches of science so that they can share their knowledge and provide feedback to each other.

An IAU Symposium presents an opportunity to formulate the direction of white dwarf studies in the next decade. The relevance of white dwarfs to so many astrophysical fields makes a meeting devoted to them and their important scientific results particularly timely. There has not been an IAU Symposium devoted to white dwarfs for many years. Indeed, the last one we can find references for was held in 1970, preceeding the 14th General Assembly. There was an IAU colloquium in 1988 and a specialist discussion meeting at the IAU General Assembly in 2003. The proposed 2019 Symposium will be highly interdisciplinary, bringing together not just astronomers working on white dwarfs, but also astronomers with expertise in cosmology, atomic physics & data, planetary system dynamics, astrometry, dark matter, astroparticle physics, exoplanets, astronomical statistics, stellar spectroscopy, stellar atmosphere theory, computational fluid dynamics, fundamental physics and others.