# G 68-34: A Double-Lined M-Dwarf Eclipsing Binary in a Hierarchical Triple System

**Authors:** Emily K Pass, David Charbonneau  
**arXiv:** [2304.02466](https://arxiv.org/abs/2304.02466)  
**Date:** 2023-04-05  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2304.02466v1/

## Key points

- G 68-34 has been identified as a double-lined eclipsing binary using high-resolution spectra from TRES and photometry from sector 56 of TESS
- The pair is spin-orbit synchronized with a period of 0.655 days, and the light curve shows significant spot modulation with a larger photometric amplitude than that of the grazing eclipses
- The joint fit to the spectroscopic and photometric data obtained masses of $0.3280\pm 0.0034$M$_\odot$ and $0.3207\pm 0.0036$M$_\odot$, and radii of $0.345\pm 0.014$R$_\odot$ and $0.342\pm 0.014$R$_\odot$
- G 68-34 adds to the small but growing population of fully convective M dwarfs with precisely measured masses and radii that can be used to test models of stellar structure, confirming our understanding of these objects' spindown mechanisms
- G 68-34 also has a white dwarf primary at a separation of 9", which indicates that it is older than five billion years old based on its white-dwarf cooling age
- The binarity of G 68-34 confirms previous hypotheses about its unusual properties, including rapid rotation despite its age; this behavior was highly unexpected given our current understanding of M dwarfs' spindown processes, suggesting that this close binary companion may be responsible for this behavior
- This study provides valuable insights into the properties and behavior of fully convective M dwarfs in close binary systems, shedding light on their formation mechanisms and evolution over time

## Summary

A recent study using high-resolution spectra from the Tillinghast Reflector Echelle Spectrograph (TRES) and photometry from sector 56 of the Transiting Exoplanet Survey Satellite (TESS) has identified G 68-34 as a double-lined eclipsing binary. The pair is spin-orbit synchronized with a period of 0.655 days, and the light curve shows significant spot modulation with a larger photometric amplitude than that of the grazing eclipses. The joint fit to the spectroscopic and photometric data obtained masses of $0.3280\pm 0.0034$M$_\odot$ and $0.3207\pm 0.0036$M$_\odot$, and radii of $0.345\pm 0.014$R$_\odot$ and $0.342\pm 0.014$R$_\odot$, after marginalizing over unknowns in the starspot distribution. This system adds to the small but growing population of fully convective M dwarfs with precisely measured masses and radii that can be used to test models of stellar structure, confirming our understanding of these objects' spindown mechanisms. Interestingly, G 68-34 also has a white dwarf primary at a separation of 9", which indicates that it is older than five billion years old based on its white-dwarf cooling age. The binarity of G 68-34 confirms previous hypotheses about its unusual properties, including rapid rotation despite its age; this behavior was highly unexpected given our current understanding of M dwarfs' spindown processes, suggesting that this close binary companion may be responsible for this behavior. Overall, this study provides valuable insights into the properties and behavior of fully convective M dwarfs in close binary systems, shedding light on their formation mechanisms and evolution over time.