BINARY-STAR LIGHT-CURVE MODELS

The historical development of binary-star light-curve models is traced from the early 1900s to the present, with emphasis on recent progress . A major break with tradition occurred about 1970 when physical model s, based on equipotentials and made possible by fast computers, replac ed geometrical models. Physical models have been improving in accuracy , efficiency, generality, and user friendliness. Further improvements can be expected. Astrophysical advances due to the new models range fr om new ways to estimate mass ratios and rotation rates to confirmation of theoretical predictions about the structure of W Ursae Majoris sta rs and behavior of irradiated convective envelopes. The morphology of close binaries, including extensions to nonsynchronous rotation and or bital eccentricity, is interwoven with physical models and their appli cations. The origins and influence of the four morphological types-det ached, semidetached, overcontact, and double contact-are inseparable f rom the development of light-curve models. Parameter adjustment is an active area, with contributions on Differential Corrections, the Marqu ardt algorithm, the Simplex algorithm, and other methods for reaching a least-squares minimum. Solutions with applied constraints and simult aneous solutions of two or more kinds of observations are coming into more frequent usage. Observables other than photometric brightness inc lude radial velocity, polarization, photospheric spectral line profile s, and spectral distributions due to circumstellar flows. Some of the newer models extend into these areas and are leading to new kinds of o bserving programs.