Discovering Young Eclipsing Binary Systems with TESS Ann Sinclair1, Celia Parts1, Eric Jensen1, Kim McLeod2, Karen Collins3, John Kielkopf4 1Swarthmore College, 2Wellesley College, 3Harvard-Smithsonian Center for Astrophysics, 4University of Louisville Sample Selection We began our search for young, low-mass EBs using a set of 5007 young stellar objects (YSOs) with masses of ~0.05-1.5 M◉ identified from the APOGEE-2 spectro- scopic survey [3]. To optimize our chances of finding EBs, we first examined two subsets of these YSOs: those flagged as double-lined spectroscopic binaries and those identified as radial velocity variables. For each of these 398 targets, we used the Lightkurve package to produce cutouts of TESS full frame images and perform aperture photometry to create a series of light curves and field plots. We inspected the light curves by eye to identify potential EB systems. From these plots, we compiled a sample of potential young, low-mass EBs. Figure 5 from Pegues et al 2021 [2] Our Sample We have identified nine targets that may be young, low-mass EB sys- tems. Eight of these targets were found in star forming regions of Orion; the other in IC 348. Their periods vary from 1.7 to 15.9 days, and many exhibit non-eclipsing variability, likely caused by rotation. At least two-thirds of these targets are double-lined spectroscopic binaries. Modeling and OriNTT 429 We flattened each light curve in our sample to elimi- nate any non-eclipse variation. Using the exoplanet package, we fit preliminary models to the flattened light curves. We employed Markov chain Monte Carlo (MCMC) sampling to find the distribution of possible values for each system’s stellar parameters, with a focus on fine-tuning the eclipse times and periods that will inform follow-up observations. We obtained radial velocity measurements for our target OriNTT 429 (TIC 276662451) from spectra taken for a previous study of PMS binary systems [5]. These data allowed us to perform a full model fit on the target and more tightly constrain its stellar properties. This model fit yields primary and secondary masses of 1.15 ± 0.0180 and 1.07 ± 0.0164 M◉, respectively. We also find the system to have an elliptical orbit with an eccentricity of 0.287 ± 0.00114 and a period of 7.46 ± 5.52e-7 days. Next Steps While we have performed initial model fits for the systems in our sample, we need radial velocity measurements and multi-wavelength observa- tions of the targets to accurately determine their stellar parameters. We plan to take ground-based follow-up observations of the systems this fall and winter. Once we have these supplementary data, we will use the measurements to model each system and find its properties. We also want to extend our search to include all 5007 YSOs in the original data- set. Ultimately, we hope to use our findings to better constrain models of PMS stellar evolution. Why look for young EBs with TESS? Finding young eclipsing binaries (EBs) and determining their properties can allow us to better understand and model how stars evolve before they reach the main se- quence. At low masses, current pre-main-sequence (PMS) models do not agree with one another [1] and are not always consistent with measured stellar prop- erties [2]. Stellar parameters of EB systems can be mea- sured from observations with very few assumptions, making them ideal targets for constraining models of PMS stars. In this project, we aim to identify previously unknown young EBs using TESS data, determine their properties, and compare them to PMS models in order to help enhance the current understanding of young stellar evolution. Figure 1: Plot of measured masses for a set of PMS stars as a function of mass predict- ed by PMS evolutionary models. The points systemati- cally fall above the 1:1 ratio line, showing disagreement between the measured and predicted masses. Figure 2: Normalized light curves generated from one sector of TESS data for each of the nine EBs currently