A 2+1 + 1 quadruple star system containing the most eccentric, low-mass, short-period, eclipsing binary known

Abstract

We 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.

The Visual Survey Group: A Decade of Hunting Exoplanets and Unusual Stellar Events with Space-based Telescopes

“…In recent years, the VSG has developed a growing interest in hierarchical systems which has resulted in discoveries of triply eclipsing triple systems (Borkovits et al 2019, 2020, (Figure 4.3 and Borkovits et al 2022, Rappaport et al 2022), several quadruple systems where both binaries are eclipsing (Figure 4.4 and Borkovits et al 2018) including a strongly interacting quadruple (Rappaport et al 2017), the nearest known quadruple (Borkovits et al 2021), and the most eccentric, low-mass, short-period, eclipsing binary known (Han et al 2021), which is also part of a quadruple system. Using TESS, the VSG presented the largest catalog of newly discovered doubly eclipsing quadruple candidates (Kostov et al 2022), and also contributed to the PH-TESS discovery of a massive, compact hierarchical system (Eisner et al 2022).…”

The Visual Survey Group: A Decade of Hunting Exoplanets and Unusual Stellar Events with Space-Based Telescopes

“…In recent years, the VSG has developed a growing interest in hierarchical systems which has resulted in discoveries of triply eclipsing triple systems (Borkovits et al (2019), Borkovits et al (2020), ( 2018)) including a strongly interacting quadruple (Rappaport et al 2017), the nearest known quadruple (Borkovits et al 2021), and the most eccentric, low-mass, short-period, eclipsing binary known (Han et al 2021), which is also part of a quadruple system. Using TESS, the VSG presented the largest catalogue of newly discovered doubly eclipsing quadruple candidates (Kostov et al 2022), and also contributed to the PH-TESS discovery of a massive, compact hierarchical system (Eisner et al 2022).…”