On the M_V(peak) Versus Orbital Period Relation for Dwarf Nova Outbursts

Abstract

We present computations for the accretion disk limit cycle model in an attempt to explain the empirical relation for dwarf nova outbursts between the peak visual absolute magnitude and orbital period found by Warner. For longer period systems one sees intrinsically brighter outbursts. This is accounted for in the limit cycle model by the scaling with radius of the critical surface density $\Sigma_{max}$ which triggers the dwarf nova outbursts. During the storage phase of the instability the accretion disk mass must be less than some maximum value, a value which scales with radius and therefore orbital period. When the instability is triggered and the accumulated mass is redistributed into a quasi steady state disk in outburst, the resultant peak optical flux from the disk is a measure of the total mass which was stored in quiescence. We compute light curves for a range in outer disk radius (or equivalently, orbital period), and find that our peak values of $M_V$ are within $<1$ mag of the observed relation $M_V$(peak)$=5.64-0.259P_{orbital}$(h) for $2\la P_{orbital}$(h)$ \la 8$.