Using the Tillinghast Reflector Echelle Spectrograph (TRES) and the Transiting Exoplanet Reconnaissance Satellite (TESS), astronomers from the Harvard-Smithsonian Center for Astrophysics (CfA) have detected the M-dwarf companion of a nearby M-dwarf star designated G 68-34. The discovery was posted on April 5 on a preprint server arXivdefines G 68-34 as a binary eclipsing an M-dwarf double.
Discrete, Double Line, Eclipsed Spectral Binaries (DLEBs) are essential for astronomers testing stellar models. This is due to the fact that the masses and radii of both stars can be measured directly from the light and radial velocity curves of the system.
At a distance of about 127 light-years from Earth, G 68-34 is a nearby M-dwarf, forming a binary widely separated (by 9 arcseconds) with a white dwarf known as LP 463-28. Previous observations of this M white dwarf pair found that G 68-34 rotates for 0.655 days, and that the system is more than five billion years old based on the white dwarf’s cooling age.
Given that G 68-34 has an abnormally fast spin, CfA’s Emily K. Pass and David Charbonneau hypothesize that G 68-34 may be a close duo. They recently obtained high-resolution spectra using TRES and photometry from TESS to verify this hypothesis.
“We observed G 68-34 using the TRES spectrograph on the 1.5-meter telescope at the Fred Lawrence Whipple Observatory (FLWO). We observed the star in eight periods between September 2022 and January 2023, with exposures between 2160 and 3600 seconds depending on sky conditions. … G 68-34 was observed with a two-minute rhythm by TESS in its sector 56, which occurred in September 2022, the researchers wrote.
Observations first confirmed that G 68-34 is indeed a double-lined spectral binary. Furthermore, photometry from TESS revealed that the pair is also eclipsing, making it a double eclipsing duo.
By analyzing the collected data, it was found that G 68-34 consists of two M dwarfs. The radii of the primary and secondary stars are 0.345 and 0.342 solar radii, while their masses are 0.328 and 0.32 solar masses, respectively. The astronomers note that G 68-34 is thus an M-dwarf binary of roughly equal mass, with both components likely fully shielded.
The age of binary G 68-34 has not yet been determined. However, given that the massively detached white dwarf’s proto-LP 463-28 has a cooling age of five billion years, G 68-34 should be at least that old. The researchers added that it is necessary to know how long LP 463-28 has been on the main sequence in order to calculate the total age of G 68-34.
Summarizing the results, the paper’s authors estimate that the total age of G 68-34 is about 6.7 billion years. They concluded that the galactic kinematics of this system indicate that it is part of the galactic disk.
Emily K Pass et al., G 68-34: M-Dwarf eclipse binary in a tripartite hierarchical system, arXiv (2023). doi: 10.48550/arxiv.2304.02466
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