Parametric SED Modelling of Protoplanetary Discs: Validation and Application to an Unstudied YSO

Abstract

We present a physically motivated spectral energy distribution (SED) modelling framework for deriving stellar and circumstellar disc parameters from broadband photometry. The model combines a parametrized disc structure, dust opacity, and interstellar extinction within a Bayesian Markov Chain Monte Carlo (MCMC) inference scheme, allowing correlated parameters to be constrained self-consistently. Initial parameter estimates are obtained via non-linear least-squares fitting and subsequently refined through MCMC sampling. The method is first validated using the well-studied debris disc system 49 Cet, for which the model successfully reproduces key literature properties. It is then applied to the previously uncharacterised young stellar object (YSO) candidate 2MASS J02512618+6012576, using photometric measurements compiled from multiple surveys. The resulting fit indicates a late-type pre-main-sequence star surrounded by a substantial circumstellar disc consistent with a moderately embedded Class II object. We further assess the sensitivity of the inferred parameters to the adopted extinction law and find that the high reddening required by the model is robust against variations in $R_V$. This work demonstrates that physically meaningful constraints on disc structure can be obtained from broadband SED modelling when extinction and distance are treated within a statistically consistent framework.

Figures (6)

• Figure 1: Radial optical depth profiles of the circumstellar disc for 2MASS J02512618+6012576 (in Section 4) at $\lambda = 10$, 100, and 1300 $\mu$m. The horizontal dashed line marks $\tau_\nu = 1$, corresponding to the transition between optically thick ($\tau_\nu > 1$) and optically thin ($\tau_\nu < 1$) regimes. The radial location of this transition varies with wavelength, reflecting the wavelength dependence of the dust opacity and the disc surface density structure.
• Figure 2: Radial profile of the disc aspect ratio ($H/r$) adopted in the circumstellar disc model. The vertical structure is parameterised as a power-law function of radius, $H(r) = H_0 (r / R_{\mathrm{in}})^{\beta_{\rm H}}$, where $H_0$ is the scale height at the inner disc radius $R_{\mathrm{in}}$ and $\beta_{\rm H}$ controls the disc flaring. This prescription governs the irradiation geometry and thus directly affects the resulting SED.
• Figure 3: Observed and modeled SED of 49 Cet. Individual contributions from the stellar photosphere and disc emission are shown, along with the total extincted model SED.
• Figure 4: modelling results for 2MASS J02512618+6012576. (top left) Observed SED and best-fit model, showing the total extincted flux together with stellar and disc components. (top right) Adopted disc geometry based on posterior median parameters. (bottom left) Radial temperature profile of the disc midplane. (bottom right) Radial contribution to the infrared emission, illustrating the dominant emitting regions at different wavelengths.
• Figure 5: Posterior probability distributions of the free parameters obtained from the MCMC sampling. Contours correspond to 68% and 95% confidence levels.