The Solar Neighborhood LIV: 54 Orbits of M Dwarf Multiples within 30 Parsecs with Speckle Interferometry at SOAR

TL;DR

This study expands the census of nearby M-dwarf multiples by presenting 54 orbital solutions derived from 1066 speckle measurements with HRCam on SOAR, spanning 0.67–30 yr in $P_ ext{orb}$ and delivering dynamical masses with 0.7–7% precision. By integrating SOAR imaging with literature astrometry and selective radial-velocity data, the authors produce 28 new orbits and revise 26, increasing the known M-dwarf orbital inventory within ~25 pc by ~11% (ORB6) and enabling robust mass-luminosity analyses for the lowest-mass stars. The paper details data acquisition, reduction, and calibration, and discusses the complementarity of imaging and RV techniques, as well as comparisons with Gaia NSS results for overlapping systems. The work lays groundwork for future, larger-scale orbital studies combining ground-based speckle, long-baseline astrometry, and Gaia/LSST data to understand the formation and dynamical evolution of low-mass multiple systems. The resulting dynamical masses will refine the mass-luminosity relation and inform studies of age, magnetism, and metallicity effects on low-mass stellar luminosities.

Abstract

We present 1066 speckle measurements of M dwarf multiples observed over 2021-2024, all taken with HRCam on the Southern Astrophysical Research 4.1 m telescope. Among these, 900 observations resolve companions in 212 pairs, with separations spanning 17 milliarcseconds to 3.4 arcsec and brightness differences ranging from 0 to 4.9 magnitudes in the I filter. We have characterized the orbits of 54 of these companions, spanning periods of 0.67-30 yr, by combining our data with literature astrometry, radial velocities, and, in four cases, Hipparcos-Gaia accelerations. Among the orbits presented here are 28 that are the first-ever such characterizations for their systems, and 26 that revise previously-published orbits, thus providing a significant update to the observed dynamics of M dwarfs in the solar neighborhood. From these orbits, we provide new and updated dynamical total masses for these systems, precise to 0.7-7% in nearly all cases. Future mass derivations for components in these systems will contribute to efforts in refining the mass-luminosity relation for the smallest stars, and will enhance investigations of age, magnetism, and metallicity effects on luminosities at a given mass.

Figures (9)

• Figure 1: Color-magnitude diagram illustrating the distribution of targets in our sample with respect to the M dwarf main sequence. Each light or dark blue point is a pair that has been resolved at SOAR (filled dark blue circles) or has been observed but not resolved (open light blue circles); their photometry measurements are listed in Vri22. The 54 points circled in black are pairs for which an orbit is presented in this paper. To illustrate the rest of the low-mass main sequence, these points are overlaid on M and L dwarfs within 25 pc (light grey points) from the RECONS astrometry program Hen18.
• Figure 2: Separation $\rho$ vs. magnitude difference $\Delta I$ for M dwarf pairs resolved at SOAR, including all of our program observations through 2019--2024 Vri22 but excluding those for which the data were noisy (":" in Table \ref{['tab:results']}). The formal diffraction limit of SOAR in the $I$ filter is 41 mas and is marked by the vertical dotted line. Measurements at smaller separations and small $\Delta I$, achieved by modeling asymmetric power spectra, are less accurate but still useful for orbit monitoring.
• Figure 3: Orbits of M dwarf systems determined from the imaging data in Table \ref{['tab:results']}. One system shown here (GJ 84 AB) also incorporated the RV data in Table \ref{['tab:RVdata']}; its corresponding RV fit is shown in Figure \ref{['fig:RVorbits']}. Each orbit's parameters are given in Table \ref{['tab:orbits']} or Table \ref{['tab:RVorbits']}, as fit by the code ORBIT ($\S$\ref{['sec:orbits']}). The points mark observations from SOAR (filled circles) and the literature (open circles), with each indicating the location of the secondary star with respect to the primary (marked by the filled black star). Uncertainties on each observation are plotted here as error bars, but are often smaller than these point sizes. In each plot, the dotted line shows the location of the periastron and the red arrow shows the direction of motion.
• Figure 4: Orbits of M dwarf systems determined from the data presented in Table \ref{['tab:results']}. One system shown here (GJ 2060 AB) also incorporated the RV data in Table \ref{['tab:RVdata']}; its corresponding RV fit is shown in Figure \ref{['fig:RVorbits']}. For additional details, see the caption to Figure \ref{['fig:orbits']}.
• Figure 5: Orbits of M dwarf systems determined from the data presented in Table \ref{['tab:results']}. One system shown here (LHS 3117 AB) also incorporated the RV data in Table \ref{['tab:RVdata']}; its corresponding RV fit is shown in Figure \ref{['fig:RVorbits']}. For additional details, see the caption to Figure \ref{['fig:orbits']}.