In two KX Cancri TESS eclipse models, continuous 1000 ppm flux changes shift the fitted time difference by 93.82 s
We provide a tool to calculate how bounded flux changes can move fitted eclipse times. It includes all free shape and brightness trend terms. We apply it to models fitted to the KX Cancri secondary eclipses in TESS sectors 21 and 47. The two continuous flux changes are independent. Each has an absolute amplitude of at most 1000 parts per million and a slope of at most 1000 parts per million per hour. Each change is zero outside a stated eclipse interval. Interior knots are at most 30 minutes apart. A linear program gives a largest local shift of 93.82297 s in the fitted time difference. Constructed curves give +93.82101 s and -93.82228 s in full nonlinear fits. Thirty time-difference tests use 60 event refits at three amplitudes and five slope settings. For the time difference, linear predictions and full refits agree within 0.040 s. For individual event times, the largest error is 0.144 s. Changes in knot spacing and support give linear bounds from 91.77 to 94.44 s at the same amplitude and slope. The amplitude limit is an input assumption. This test does not infer an actual bias in the observed times, a physical spot map, or a global nonlinear bound. Earlier SCI work already measured a 17 s selection effect in these eclipses. Our contribution is a reproducible response calculation under explicit amplitude and slope limits. We preserve source FITS files, source hashes, code, fit terms, response rows, constructed curves, full refit results, and figures.
KX Cancri · TIC 332146607 · TESS · eclipsing binary · eclipse timing · systematic error · bounded flux distortion · least squares · linear programming · reproducible methods
References
7- supersedesIn two KX Cancri TESS eclipse models, continuous 1000 ppm flux changes shift the fitted time difference by 93.82 s sci:sha256:6e32f144ef16ff051ec2509c160327805d9b60ed4d33556f02c85f41cef475c1
We clarify that the 0.040 s agreement applies to the time difference. We add the 0.144 s maximum error for individual event times. The source data, constructed curves, bounds, and full refits are the same.
- usesOuter eclipse data change the fitted KX Cancri timing shift by 17 seconds in TESS sectors 21 and 47 sci:sha256:199eb11571d3a6b7ad39c63621572f7bd06308da0dd5738d773c2de601ab3866
This signed SCI study already reports selection effects, depth markers, and missing clean primary data in the same visits. Its 17 s selection effect gives a comparison scale. We add a response test under explicit amplitude and slope limits.
- usesdoi:10.17909/t9-nmc8-f686
We use the public TESS SPOC light curves for TIC 332146607 in sectors 21 and 47. The exact objects and hashes are preserved.
- usesdoi:10.48550/arXiv.2012.05977
We use the orbit geometry and reference period. This work also reports spots and corrected-flux defects in the 2020 visit.
- doi:10.1051/0004-6361/202040004
This work measured KX Cancri apsidal motion with ground data and the 2020 TESS visit. It gives the physical context for precise eclipse times.
- doi:10.1051/0004-6361/201321309
This prior work shows that stellar spots can bias fitted transit times. We cite this established effect and do not claim its first detection.
- usesdoi:10.1086/683602
We use batman to calculate the local spherical eclipse profiles.
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