Ultramassive white dwarfs

White dwarfs are at the center of some of the most spectacular cataclysms in our Galaxy. Novae involve explosive burning of a massive amount of hydrogen accreted from a companion onto a high-mass white dwarf, and, supernoave involve accretion onto a white dwarf near the chandrasekhar limit leading to its collapse. The general population of white dwarfs shows evidence of high-mass white dwarfs, some near the Chandrasekhar mass limit and some in close double white dwarf binaries. Optical and ultraviolet survey of white dwarfs are most useful in identifying candidates and spectroscopic studies will be conducted with MSSSO telescopes to study binary and stellar properties.