Large TESS pixels typically capture light from multiple stars, and the data processing pipeline subtracts the estimated contributions of contaminant stars from the light curves it produces. If these crowdedness factors (recorded as the header keyword CROWDSAP) are not exact, they will cause systematic errors on measurements of transit depths and variability amplitudes. We are performing an independent determination of estimated CROWDSAP factors by comparing the depths of binary eclipses between TESS light curves and ground-based data from ASAS-SN with a Markov Chain Monte Carlo analysis. This allows us to accurately appraise the precision of pipeline CROWDSAP factors, the uncertainty on which should be incorporated into TESS analyses as an extrinsic error.

{"references": ["Stumpe et al. 2012, PASP, 124, 985. doi:10.1086/667698", "Dalba,et al. 2017, AJ, 153, 59. doi:10.1088/1361-6528/aa5278", "Kochanek et al. 2017, PASP, 129, 104502. doi:10.1088/1538-3873/aa80d9", "Foreman-Mackey et al. 2013, Astrophysics Source Code Library. ascl:1303.002", "Maxted, P.~F.~L. 2016, AAP, 591, A111. doi:10.1051/0004-6361/201628579", "Morton, T.~D. 2015, Astrophysics Source Code Library. ascl:1503.010"]}