Paper

NGTS-EB-7, an eccentric, long-period, low-mass eclipsing binary

Henning, Thomas, O'Brien, Sean M, Hawthorn, Faith, Lendl, Monika, Jordán, Andrés, Marcelo Tala Pinto, Hobbs, Katlyn L, Casewell, Sarah L, McCormac, James, Saha, Suman, Wheatley, Peter J, Doyle, Lauren, Bayliss, Daniel, Alves, Douglas R, Gillen, Edward, Jenkins, James S, Ulmer-Moll, Solène, Freckelton, Alix V, Eberhardt, Jan, Watson, Christopher A, Gill, Samuel, Kendall, Alicia, Brahm, Rafael, Yoshi Nike Emilia Eschen, Jorge Fernández Fernández, Wilson, Thomas G, Maxted, Pierre F L, Ernst J W de Mooij, Apergis, Ioannis, Burleigh, Matthew R, Rodel, Toby, Trifonov, Trifon, Goad, Michael R, Helled, Ravit, Costes, Jean C, Bouchy, Francois, Udry, Stéphane, Dumusque, Xavier

2025

Overview

Despite being the most common types of stars in the Galaxy, the physical properties of late M dwarfs are often poorly constrained. A trend of radius inflation compared to evolutionary models has been observed for earlier type M dwarfs in eclipsing binaries, possibly caused by magnetic activity. It is currently unclear whether this trend also extends to later type M dwarfs below the convective boundary. This makes the discovery of lower-mass, fully convective, M dwarfs in eclipsing binaries valuable for testing evolutionary models especially in longer-period binaries where tidal interaction between the primary and secondary is negligible. With this context, we present the discovery of the NGTS-EB-7 AB system, an eclipsing binary containing a late M dwarf secondary and an evolved G-type primary star. The secondary star has a radius of \\(0.125 \\pm 0.006 R_\\odot\\) , a mass of \\(0.096 \\pm 0.004 M_\\odot\\) and follows a highly eccentric \\((e=0.71436 \\pm 0.00085)\\) orbit every \\(193.35875 \\pm 0.00034\\) days. This makes NGTS-EB-7 AB the third longest-period eclipsing binary system with a secondary smaller than \\(200 M_J\\) with the mass and radius constrained to better than \\(5 \\%\\). In addition, NGTS-EB-7 is situated near the centre of the proposed LOPS2 southern field of the upcoming PLATO mission, allowing for detection of the secondary eclipse and measurement of the companion`s temperature. With its long-period and well-constrained physical properties - NGTS-EB-7 B will make a valuable addition to the sample of M dwarfs in eclipsing binaries and help in determining accurate empirical mass/radius relations for later M dwarf stars.

• Publisher: Cornell University Library, arXiv.org
• Subject: Constraints / Eclipsing binary stars / Physical properties / Red dwarf stars