Eclipse Timing Variations of Circumbinary Substellar Objects in TESS Data

Abstract: Circumbinary planets and brown dwarfs form in complex gravitational environments, offering insights into formation, orbital stability, and habitability prospects. However, they remain underrepresented, with only 60 confirmed or candidate systems known. In this work, we leverage TESS photometry to search for circumbinary companions through eclipse timing variations (ETVs), analyzing 152 detached eclipsing binaries. By modeling eclipse timings, we identify 26 systems with significant periodic signals, 14 of which have false alarm probabilities below 0.01. While no detections are confirmed, TIC 350297040 emerges as a candidate for a circumbinary brown dwarf ($0.06~M_{\odot}$) under the assumption of a $1~M_{\odot}$ binary system, though further investigation is required. Simulations using synthetic ETVs indicate a 5\% recovery rate for circumbinary brown dwarfs and 0.1\% for Jupiter-like planets, with median masses of $56.6^{+16.5}{-23.4}~M_{\rm J}$ and periods of $1404^{+1361}_{-953}$ d. Our simulations show that the smallest detectable mass is $1.6~M_{\rm J}$ at a period of 1860 d and confirm that ETV methods are effective in detecting misaligned systems. In the absence of a detection, we set an upper limit of 40\% on the occurrence rate of circumbinary brown dwarfs at the 2$\sigma$ confidence level, while a confirmed single detection would imply an occurrence rate of 13.08\%. These constraints are consistent with previous abundance estimates for circumbinary brown dwarfs ($\lesssim6.5\%$) but motivate a larger sample size. Furthermore, the very low recovery rates provide insights into the debate on first- and second-generation planet formation around post-common envelope binaries.