I will present an overview of work carried out by my collaborators and myself that aims to characterize the long-term variations of broad emission lines seen in quasar spectra and interpret those variations in the context of models for the line-emitting gas. I will begin with a pedagogical introduction to quasars and their broad-line regions and then I will describe in broad terms the types of long-term variability that we observe. I will then describe modeling tools that I have developed and the lessons that we have learned by studying the variations of the broad emission lines. I will close by describing the AQMES program that is part of SDSS-V, which will produce an enormous set of data suitable for studying the long-term variability of a large number of quasars.
Seminar held in 538 Davey or via Zoom: https://psu.zoom.us/j/93131536409