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M. Politano (Ariz. St. U.), U. Kolb (U. Leicester), I. Baraffe (Obs. Lyon)
Significant advances in both our theoretical and observational understanding of brown dwarfs (BDs) have occurred within the past few years. In particular, theoretical models of BDs, including improved internal physics and non-gray atmosphere models, have proven to be reliable in matching the photometric and spectroscopic properties for a number of BDs. Such important advances now offer an excellent opportunity to apply these models to the secondaries in cataclysmic variables (CVs).
In this paper, we present preliminary results of population synthesis calculations of the formation and subsequent evolution of CVs with BD secondaries. These models extend the standard model of CV formation and evolution which describes CVs born with stellar (main sequence) secondaries. The population synthesis calculations utilize a standard birthrate code for CVs which has been modified to calculate the formation of CVs with substellar secondaries, and a binary evolution code which uses full stellar models for the BD secondary rather than a polytropic approximation.
Some fraction of CVs which form with BD secondaries will have orbital periods shorter than 80 minutes (the orbital period minimum for CVs which are born with stellar secondaries). These systems may provide a viable model for V485 Cen, a hydrogen-rich CV with an orbital period of 59 mins. In addition, these calculations allow us to test a variety of initial mass ratio distributions for the progenitor binaries. Consequently, there is the potential to use models of the formation of CVs with BD secondaries to place constraints on the mass ratio distribution of primordial binaries which contain a main sequence star of low or intermediate mass (1--8 solar masses) and a BD secondary in a wide orbit (~10--1000 days). Acquiring information about such systems by direct observation is currently either extremely difficult or impossible.