Multiwavelength are studies of cool stars with TESS and Chandra/HETG

We present a comparison between the plasma properties of accreting Classical T-Tauri Stars (CTTS) and the coronal Main Sequence (MS) stars seen with Chandra/HETG and the characteristics of their TESS lightcurves. Our analysis reveals that the temperature diagnostics (provided by (i) the ratio of H-like to He-like X-ray emission of Si, Mg, Ne, O versus individual line luminosities, and (ii) ratio of H-like to He-like X-ray emission of each line plotted against the ratio of H-like to He-like of another) both exhibit a positive correlation. Interesting, these correlations are independent of the stars' flaring activity during their X-ray or optical observations. This is contrary to our expectation that X-ray flares should cause increased plasma temperature and demonstrate a need for detailed  flare characterization in optical and X-rays. We are continuing our study to correlate the  flaring behaviour of these stars against their fundamental properties (e.g., rotation periods, mass, age, abundance).