We present a detailed comparison of two approaches, the use of a precalculated database and simulated annealing （SA）, for fitting the continuum spectral energy distribution （SED） of astrophysical objects whose appearance is dominated by surrounding dust. While pre-calculated databases are commonly used to model SED data, only a few studies to date employed SA due to its unclear accuracy and convergence time for this specific problem. From a methodological point of view, different approaches lead to different fitting quality, demand on computational resources and calculation time. We compare the fitting quality and computational costs of these two approaches for the task of SED fitting to provide a guide to the practitioner to find a compromise between desired accuracy and available resources. To reduce uncertainties inherent to real datasets, we introduce a reference model resembling a typical circumstellar system with 10 free parameters. We derive the SED of the reference model with our code MC3 D at 78 logarithmically distributed wavelengths in the range [0.3 μm, 1.3 mini and use this setup to simulate SEDs for the database and SA. Our result directly demonstrates the applicability of SA in the field of SED modeling, since the algorithm regularly finds better solutions to the optimization problem than a precalculated database. As both methods have advantages and shortcomings, a hybrid approach is preferable. While the database provides an approximate fit and overall probability distributions for all parameters deduced using Bayesian analysis, SA can be used to improve upon the results returned by the model grid.
We present modeling work on three young stellar objects that are promis-ing targets for future high-resolution observations to investigate circumstellar disk evolution. The currently available data comprise the spectral energy distribution from optical to millimeter wavelengths which allow constraining the structure of the cir-cumstellar disk using self-consistent radiative transfer models. The results suggest that the assumption of well-mixed dust and gas leads to overestimation of flux in the far-infrared. Observational and theoretical arguments suggest that an overall decrease in far-infrared excess can be explained by dust settling towards the midplane. A new disk model is hence employed to take the effect of dust sedimentation into account. The extended model satisfactorily reproduces all existing observations. The three tar-gets studied here therefore deserve follow-up observations to reveal the evolutionary state of their protoplanetary disks.
