Han, E.Rappaport, S.A.Vanderburg, A.Tofflemire, B.M.Borkovits, T.Schwengeler, H.M.Zasche, P.Krolikowski, D.M.Muirhead, Philip S.Kristiansen, M.H.Terentev, I.A.Omohundro, M.Gagliano, R.Jacobs, T.LaCourse, D.2022-01-032022-01-03E. Han, S.A. Rappaport, A. Vanderburg, B.M. Tofflemire, T. Borkovits, H.M. Schwengeler, P. Zasche, D.M. Krolikowski, P.S. Muirhead, M.H. Kristiansen, I.A. Terentev, M. Omohundro, R. Gagliano, T. Jacobs, D. LaCourse. "A 2+1+1 quadruple star system containing the most eccentric, low-mass, short-period, eclipsing binary known." Monthly Notices of the Royal Astronomical Society, https://doi.org/10.1093/mnras/stab35070035-87111365-2966https://hdl.handle.net/2144/43522We present an analysis of a newly discovered 2+1+1 quadruple system with TESS containing an unresolved eclipsing binary (EB) as part of TIC 121088960 and a close neighbor TIC 121088959. The EB consists of two very low-mass M dwarfs in a highly-eccentric (e = 0.709) short-period (P = 3.04358 d) orbit. Given the large pixel size of TESS and the small separation (3${^{\prime\prime}_{.}}$9) between TIC 121088959 and TIC 121088960 we used light centroid analysis of the difference image between in-eclipse and out-of-eclipse data to show that the EB likely resides in TIC 121088960, but contributes only ∼10% of its light. Radial velocity data were acquired with iSHELL at NASA’s Infrared Facility and the Coudé spectrograph at the McDonald 2.7-m telescope. For both images, the measured RVs showed no variation over the 11-day observational baseline, and the RV difference between the two images was 8 ± 0.3 km s−1. The similar distances and proper motions of the two images indicate that TIC 121088959 and TIC 121088960 are a gravitationally bound pair. Gaia’s large RUWE and astrometric_excess_noise parameters for TIC 121088960, further indicate that this image is the likely host of the unresolved EB and is itself a triple star. We carried out an SED analysis and calculated stellar masses for the four stars, all of which are in the M dwarf regime: 0.19 M⊙ and 0.14 M⊙ for the EB stars and 0.43 M⊙ and 0.39 M⊙ for the brighter visible stars, respectively. Lastly, numerical simulations show that the orbital period of the inner triple is likely the range 1 to 50 years.en-US© 2021 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.Article10.1093/mnras/stab3507694498