Cataclysmic variable stars (CVs) are a broad class of close binaries in which a white dwarf gains mass from a companion, which usually resembles a late-type main-sequence dwarf. As the name implies, most types of CVs are subject to large, rapid variations in brightness, ranging from nuclear explosions of accreted material in the classical novae to the gentler (but still dramatic) flareups of the dwarf novae, now almost universally considered to result from episodic accretion of material accumulated in a disk around the white dwarf. If the white dwarf has a strong magnetic field, a host of other phenomena (coherent pulsations, copious X-ray flux, accretion through a column) present themselves.
Exciting and important discoveries about CVs rest on fundamental astronomical measurements - without such basic information it is extraordinarily difficult to make progress on our understanding of these systems by characterizing their properties and constraining models of their behaviors. Here, large allocations of guaranteed observing time, primarily at the MDM Observatory at the Kitt Peak National Observatory, will be used to make such measurements. First, a long-standing and very productive program of orbital period determinations through radial velocity measurements will be continued, encompassing a wide sample of CVs. This program frequently turns up interesting new objects. Second, an ongoing program of parallax measurements and direct imaging of selected CVs will be continued. This program produces very accurate parallaxes and proper motions, which have already had substantial impact. The astrometric work will culminate in a careful re-evaluation of the CV space density, which is an important observable predicted by binary-star evolution models. Small amounts of telescope time will be used to clarify bad identifications and other catalog anomalies.
This project will provide several opportunities for student research. Undergraduate students at Dartmouth will participate in the acquisition, interpretation, and analysis of this data. This grant will also support a graduate student who will be trained in the field of CV research. The work will generate useful astronomical software, and in particular result in continued refinement and revision of the widely-used ""skycalc"" time-and-the-sky program.
