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Abstract

Proplyds are disks around young low-mass stars inside M42 photoevaporated by ultraviolet radiation from the massive Trapezium stars. Recent spectrophotometry gives tantalizing evidence of abundance differences between proplyds and the surrounding nebula, with important implications for the evolution of protoplanetary disks. However, proplyds are highly structured at very small 6 scales, which must be taken into account in any abundance analysis. We present physical models of the proplyds that combine a simplified (but realistic) treatment of the acceleration of the flow through the ionization front with a detailed calculation of the radiative transfer, ionization, and thermal balance using the CLOUDY code. We predict the emissivity structure in multiple emission lines, together with the flux, morphology and kinematic profile of any given line. Comparison with high-resolution imaging, high-dispersion spectroscopy, and deep spectrophotometry tightly constrains the model parameters, giving abundances much more reliably than can be achieved by empirical methods.