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

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 $M_{\mathrm{B}+\mathrm{C}}=0.48\pm 0.14M_{\odot }$. We show from the companions relative motions that they are of equal mass (with a mass ratio of $1.00\pm 0.03$), thus $0.24\pm 0.07M_{\odot }$ 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 $8.41_{-0.02}^{+0.04}$years.

arXiv comment9 pages, 7 figures, accepted for publication in Astronomy & Astrophysics

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