2019 HotSci at STScI

Name: Jeff Cummings 
Title: Constraining Stellar Rotation, Internal Mixing, and AGB Stars Using The Initial-Final Mass Relation
Abstract: Analysis of white dwarfs, the remnants of a majority of stars, provide significant insight on the evolutionary processes that occur during a star's life. Because of their simple, typically pure hydrogen atmospheres, spectroscopic observations of white dwarfs allow straightforward determination of their masses, cooling ages, and atmospheric parameters. Observed in the contexts of known stellar populations, they can then be connected to the mass and characteristics of a star that would produce such a white dwarf. This initial-final mass relation now provides a powerful connection between stars from 0.85 to 7.5 Msun and the white dwarfs they form. As our understanding of this relation improves, in lower-mass stars (< 3 Msun) it is continuing to inform us about their poorly understood mass-loss rates, dredge-up processes, core-mass evolution, and their connection to carbon stars. In higher-mass stars (> 3 Msun) it is also beginning to directly constrain the effects of convective-core overshoot and rotation on core evolution, two processes that are difficult to model and up until now have been poorly constrained by observations.

Name: Karl Gordon 
Title: Milky Way optical and mid-IR extinction curves
Abstract: Interstellar dust extinction in the optical and mid-infrared (MIR) wavelength ranges is characterized by an overall decreasing extinction with increasing wavelength with superimposed broad extinction features. I will present work focused on measuring the spectroscopic dust extinction in these two wavelength ranges. The first study gives the first truly spectroscopic measurement of the diffuse ISM MIR extinction based on a sample of sightlines observed by the Spitzer Space Telescope. This new measurement provides the full 5-40 micron average extinction curve including profiles for the the two silicate grain diagnostic features at 10 and 20 microns. The second study uses HST/STIS spectra to perform the first systematic spectroscopic study of optical extinction in the Milky Way. This study has revealed that the Very Broad Structure in optical extinction is due to three broad extinction features, two of which have strengths that intriguingly correlate with the 2175 A extinction feature. The results of these two studies provide new constraints on dust grain properties and empirical averages useful for modeling and/or correcting for the effects of dust extinction on background sources.