Stars, Planets, and ISM Seminar

Jayden Blanchard, The University of Texas at Austin

Laboratory Measurements of Carbon at White Dwarf Photospheric Conditions

White dwarfs are the end result of over 98% of all stars. Hot and warm DQs are white dwarf (WD) subclasses with C/O dominated atmospheres. These objects are likely results of WD-WD mergers, and accurate modeling of them can lead to a better understanding of the merger process and therefore the type Ia SNe process. Using the Z platform at Sandia National Laboratories (SNL), we are able to generate plasmas at WD photospheric conditions, allowing for benchmark measurements of DQ spectra. I will use the Z platform to benchmark CI and CII spectra and compare the results to state-of-the-art theoretical models. These current theoretical models disagree, so laboratory measurements will help to resolve these discrepancies and lead to more accurate log g and T_eff determinations for C atmosphere WDs.

Nina Filippova, The University of Texas at Austin

Non-ideal MHD and Protostellar Feedback Effects on Disk Formation and Evolution in Numerical Simulations of Star Cluster Formation

Protostellar disks are expected to form early during the star formation process due to conservation of angular momentum throughout the collapse. While recent surveys by the Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA) have resolved disks around hundreds of nearby protostars, numerical simulations assuming ideal magnetohydrodynamics (MHD) have historically struggled to achieve disk formation – the “magnetic braking catastrophe.” Non-ideal MHD effects, which become relevant at the low ionization fractions typical of molecular clouds, have been shown to reduce the effectiveness of magnetic braking. However, most numerical studies of disk formation also adopt highly-idealized initial conditions of isolated, uniform-density spherical cores collapsing to form individual protostars. This setup may exaggerate the influence of magnetic braking. Furthermore, most stars are born as members of bound systems, and dynamical interactions between stellar neighbors likely affect subsequent disk evolution. It is therefore clear that a comprehensive study of disk formation and evolution must incorporate both external dynamics as well as increasingly sophisticated physics. In this talk, I will present the results from a suite of numerical calculations following the collapse of a turbulent, magnetized 50 solar-mass core down to the formation of stellar clusters and disks using the 3D radiation+gravity MHD code GIZMO, with additional modules for protostellar feedback developed within the STARFORGE numerical framework. These simulations aim to investigate the effects of including non-ideal MHD and realistic protostellar feedback on disk formation and evolution within the context of star cluster (rather than single-star) formation.