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 _ { B + 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 .