PLANETARY REMNANTS AROUND WHITE DWARF STARS

In this dissertation we present the results of four separate searches for infrared excess emission at white dwarf stars. Using spectra from the IRTF and photometry from PAIRITEL, MMT+SWIRC, Gemini+NIRI, and Spitzer+IRAC we discover 11 new dusty WD systems. These new systems increase the population of such systems by 33%, bringing the total to 45. These discoveries also significantly expand the mass-temperature parameter space available to circumstellar dust at WDs with the discovery of the hottest, coolest, and most massive WD with dust. Future searches for WD debris disks can exploit these results to streamline their target selection. Our three massive dusty WDs also illustrate that massive main sequence stars do host planets, despite the dearth of detections in this regime using conventional planet detection methods. We find the frequency of disks at WDs to be 4.3% around a sample of typical WDs and that the frequency varies with mass. The frequency amongst our sample of massive WDs is 3%. The frequency of disks at WDs is also used to derive that WDs can accrete objects as large as the dwarf planet Ceres