Geert Barentsen, J.S. Vink, J. E. Drew, S. E. Sale

Bayesian inference of T Tauri star properties using multi-wavelength survey photometry

Figure 14. Comparison of our inferred Hα EWs with values obtained from grism spectroscopy by Dahm & Simon (2005). The grey dashed line shows the unity relation. The median error bar is shown in the bottom right. The scatter is thought to be due to a combination of uncertainty and natural Hα emission variability.


There are many pertinent open issues in the area of star and planet formation. Large statistical samples of young stars across star-forming regions are needed to trigger a breakthrough in our understanding, but most optical studies are based on a wide variety of spectrographs and analysis methods, which introduces large biases.

Here we show how graphical Bayesian networks can be employed to construct a hierarchical probabilistic model which allows pre-main sequence ages, masses, accretion rates, and extinctions to be estimated using two widely available photometric survey databases (IPHAS r’/Hα/i’ and 2MASS J-band magnitudes). Because our approach does not rely on spectroscopy, it can easily be applied to homogeneously study the large number of clusters for which Gaia will yield membership lists. We explain how the analysis is carried out using the Markov Chain Monte Carlo (MCMC) method and provide Python source code. We then demonstrate its use on 587 known low-mass members of the star-forming region NGC2264 (Cone Nebula), arriving at a median age of 3.0 Myr, an accretion fraction of 20 ± 2% and a median accretion rate of 10−8.4 M☉/yr.

The Bayesian analysis formulated in this work delivers results which are in agree- ment with spectroscopic studies already in the literature, but achieves this with great efficiency by depending only on photometry. It is a significant step forward from previous photometric studies, because the probabilistic approach ensures that nuisance parameters, such as extinction and distance, are fully included in the analysis with a clear picture on any degeneracies.

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Last Revised: 2012 November 28th