# The discrepancy between dynamical and theoretical mass in the triplet-system 2MASS J10364483+1521394

## TL;DR

This study combines new and existing astrometric data to determine the orbital parameters and individual masses of the triple system 2MASS J10364483+1521394, revealing a significant discrepancy with theoretical models.

## Contribution

It provides the first dynamical mass measurements for this system and highlights a 30% higher mass than predicted by stellar evolutionary models.

## Key findings

- Dynamical masses are 30% higher than theoretical predictions.
- The orbital period of the BC pair is approximately 8.4 years.
- Companions have nearly equal masses of about 0.24 solar masses each.

## Abstract

We combine new Lucky Imaging astrometry from NTT/AstraLux Sur with already published astrometry from the AstraLux Large M-dwarf Multiplicity Survey to compute orbital elements and individual masses of the 2MASS J10364483+1521394 triple system belonging to the Ursa-Major moving group. The system consists of one primary low-mass M-dwarf orbited by two less massive companions, for which we determine a combined dynamical mass of $M_{\rm{B}+\rm{C}}= 0.48 \pm 0.14\ M_\odot$. We show from the companions relative motions that they are of equal mass (with a mass ratio of $1.00 \pm 0.03$), thus $0.24 \pm 0.07\ M_\odot$ individually, with a separation of $3.2 \pm 0.3\ $AU and conclude that these masses are significantly higher ($30\%$) than what is predicted by theoretical stellar evolutionary models. The biggest uncertainty remains the distance to the system, here adopted as $20.1 \pm 2.0$ pc based on trigonometric parallax, whose ambiguity has a major impact on the result. With the new observational data we are able to conclude that the orbital period of the BC pair is $8.41^{+0.04}_{-0.02}\ $years.