Dynamical masses for two M1 + mid-M dwarf binaries monitored during the SPHERE-SHINE survey

Abstract

We present orbital fits and dynamical masses for HIP 113201AB and HIP 36985AB, two M1 + mid-M dwarf binary systems monitored as part of the SPHERE-SHINE survey. To robustly determine the age of both systems via gyrochronology, we undertook a photometric monitoring campaign for HIP 113201 and GJ 282AB, the two wide K star companions to HIP 36985, using the 40 cm Remote Observatory Atacama Desert telescope. Based on this monitoring and gyrochronological relationships, we adopt ages of 1.2 ± 0.1 Gyr for HIP 113201AB and 750 ± 100 Myr for HIP 36985AB. These systems are sufficiently old that we expect that all components of these binaries have reached the main sequence. To derive dynamical masses for all components of the HIP 113201AB and HIP 36985AB systems, we used parallel-tempering Markov chain Monte Carlo sampling to fit a combination of radial velocity, direct imaging, and Gaia and HIPPARCOS astrometry. Fitting the direct imaging and radial velocity data for HIP 113201 yields a primary mass of 0.54 ± 0.03 M⊙, fully consistent with its M1 spectral type, and a secondary mass of 0.145 ± M⊙. The secondary masses derived with and without including HIPPARCOS-Gaia data are all considerably more massive than the 0.1 M⊙ mass estimated from the photometry of the companion. Thus, the dynamical impacts of this companion suggest that it is more massive than expected from its photometry. An undetected brown dwarf companion to HIP 113201B could be a natural explanation for this apparent discrepancy. At an age >1 Gyr, a 30 MJup companion to HIP 113201B would make a negligible (<1%) contribution to the system luminosity but could have strong dynamical impacts. Fitting the direct imaging, radial velocity, and HIPPARCOS-Gaia proper motion anomaly for HIP 36985AB, we find a primary mass of 0.54 ± 0.01 M⊙ and a secondary mass of 0.185 ± 0.001 M⊙, which agree well with photometric estimates of component masses, the masses estimated from MK– mass relationships for M dwarf stars, and previous dynamical masses in the literature.

Updated orbital monitoring and dynamical masses for nearby M-dwarf binaries

“…This becomes even more important at the lowest stellar masses for which the current theoretical models have been shown to systematically underestimate Mdwarf masses below M ≤ 0.5 M by 5−50 % (e.g. Hillenbrand & White 2004;Montet et al 2015;Calissendorff et al 2017;Biller et al 2022). Since M dwarfs evolve slowly and remain in their pre-main sequence phase for ∼ 100 Myrs (Baraffe et al 1998), M-dwarf binaries become valuable benchmark targets for astrophysical calibrations comparing dynamical masses from observational data to isochronal models (e.g.…”

New binaries from the SHINE survey

“…4.4.1. An in depth analysis, including a full orbital solution, for HIP 36985 and HIP 113201 is presented in Biller et al (2022).…”

The SPHERE view of multiple star formation

“…This is a regime where overlaps exist between high contrast imaging and indirect dynamical methods (radial velocities and Gaia astrometry), disclosing the possibility to solve the degeneracy between masses and separation at long periods, and with inclination in radial velocities. This greatly reduces the error bars in mass determinations (see, e.g., [73]). Companions detected with multiple techniques may then be used as benchmarks for stellar evolutionary models that are useful in particular for the pre-main sequence phase.…”

“…Quite accurate results were obtained for seven systems, confirming that magnetic models better matches the observed colors. Additional interesting cases have been presented for other young low-mass systems [73,82].…”