1. Most stars occur in systems containing two or more objects. Some pairs include a very dense star called a ?white dwarf? ? a star with the mass of our Sun crammed into a volume about the size of the Earth ? plus an ordinary star smaller and redder than the Sun. In some cases, the red star can transfer a stream of mass onto a disk of gas around the white dwarf. Matter spirals in through the disk to accumulate on the white dwarf, heating up rapidly and shining brightly for a time. The resulting outburst of energy gives these so-called ?cataclysmic variables? (CVs) their name. Monitoring CVs for outbursts, or to study the wealth of periodic signals they display, requires far more telescope time than professional astronomers can afford. For the past two decades, the Principal Investigator has been leading a world-wide group of amateur astronomers using small telescopes ? which he calls the ?Center for Backyard Astrophysics? ? to obtain the necessary observations of CVs. The data have proven extremely useful to professional astronomers who study these systems. This project continues that fruitful collaboration, engaging amateurs around the world in valuable ?citizen science.?
2. Most of the information about CVs comes from various periodic signals they exhibit. Yet few professional observers have been willing to devote the time necessary to monitor these systems in order to measure period changes (which can reveal their evolutionary timescales) or to obtain data on additional periodic phenomena they may display. These include orbital periods and period changes, rotational periods, and so-called ?superhumps? in certain classes of CVs. This proposal seeks to obtain long-term time-series photometry from a world-wide network of amateur astronomers using small telescopes ? called the ?Center for Backyard Astrophysics? or CBA ? to fill this need. In addition, the Principal Investigator expects to be able to use the data obtained to help distinguish between two diametrically opposed theories for the fate of CV systems: Are the donor stars whittled away by mass transfer to the white dwarf primary, or are they evaporated by nova explosions on the white dwarfs? The photometric time-series data and their implications for improving our understanding of CVs constitute the Intellectual Merit of this project. The Broader Impacts of this project stem from the Principal Investigator?s continuing ability to motivate and engage the world-wide community of amateur astronomers to gather scientifically useful photometric data on these systems. The amateur observers willingly and continually fill the gap in observational data that has been largely abandoned by the professionals, and under the leadership of the Principal Investigator they produce a steady stream of valuable photometric data on a wide variety of CVs.
