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 neighbour TIC 121088959. The EB consists of two very low-mass M dwarfs in a highly eccentric (e = 0.709) short-period (P = 3.043 58 d) orbit.
Given the large pixel size of TESS and the small separation (3.'' 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 similar to 10 per cent of its light. Radial velocity data were acquired with iSHELL at NASA's Infrared Facility and the Coude spectrograph at the McDonald 2.7-m telescope.
For both images, the measured RVs showed no variation over the 11 d 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-circle dot and 0.14 M-circle dot for the EB stars and 0.43 M-circle dot and 0.39 M-circle dot for the brighter visible stars, respectively.
Lastly, numerical simulations show that the orbital period of the inner triple is likely the range 1-50 yr.