Fundamental properties of the pre-main sequence eclipsing stars of MML 53 and the mass of the tertiary
2019
We present the most comprehensive analysis to date of the Upper
CentaurusLupus
eclipsingbinary MML 53 (2.097892 d), and for the first time, confirm the bound-nature of the third star (~9yr orbit). Our analysis uses new and archival spectra and time-series photometry. We determined the temperature of the primary star to be 4880+-100 K. The study of the close binary incorporated treatment of spots and dilution by the tertiary in the light curves, allowing for the robust measurement of the masses of the
eclipsingcomponents within 1% (M1=1.0400+-0.0067 and M2=0.8907+-0.0058 Msun), their radii within 4.5% (R1=1.283+-0.043 and R2=1.107+-0.049 Rsun), and the secondary temperature (4379+-100K). From the analysis of the
eclipsetimings, and the change in systemic velocity of the
eclipsingbinary and the radial velocities of the third star, we measured the mass of the outer companion to be 0.7 Msun within 20%. The age we derived from the evolution of the temperature ratio between the
eclipsingcomponents is fully consistent with previous estimates of the age of UCL (16+-2 Myr). At this age, the tightening of the MML 53
eclipsingbinary has already occurred, thus supporting close-binary formation mechanisms that act early in their evolution. The
eclipsingstars roughly follow the same theoretical isochrone, but appear to be inflated in radius (by 20% for the primary and 10% for the secondary). However, our primary radius measurement of is in full agreement with the independent measurement of the secondary of NP Per which has the same mass and a similar age. The
eclipsingstars of MML 53 are found to be larger but not cooler than predicted by non-magnetic models, it is not clear what is the mechanism that is causing the radius inflation given that activity, spots and/or magnetic fields slowing their contraction, require the inflated stars to be cooler to remain in thermal equilibrium.
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