The Ca II lines as tracers of the magnetospheric accretion flows: the Chamaeleon I star-forming region

According to the prevailing model, the broad emission lines characteristic of low mass, accreting young stars (Classical T Tauri Stars, CTTS) are formed in magnetospheric accretion flows. Current models rely on empirical temperature structures and geometries. Modeling lines arising from a variety of elements in different ionization stages can help constrain the temperature structure and the geometry and provide better determinations of the accretion rates. Our goals are to model the Ca II in CTTS to understand their formation and, assuming that the magnetospheric model is valid, use them to refine it, in particular, to constrain the temperature and geometry. We followed the methods of Muzerolle et al. (2001) to calculate the Ca II H, K, and IR Triplet lines for an extensive grid of magnetospheric models and used X-shooter spectra of 21 CTTS stars from the Chamaeleon I region (Manara et al. 2016,2017) to test the predictions of the magnetospheric accretion model. We find agreement between model predictions inferred from different lines. Preliminary fitting to the observations suggests that stars with the higher mass accretion rates have smaller disk truncation radius. More refined modeling to a larger set of stars, currently underway, is required to confirm this tantalizing suggestion.