Absolute parameters of young stars: GG Lup and μ1 Sco

Abstract

New high-resolution spectroscopy and $BVR$ photometry, together with literature data, on the Gould's Belt close binary systems GG Lup and $\mu^1$ Sco are presented and analysed. In the case of GG Lup, light and radial velocity curve fittings confirm a near-Main-Sequence picture of a pair of close stars. Absolute parameters are found, to within a few percent, thus: $M_1$ = 4.16$\pm$0.12, $M_2$ = 2.64$\pm$0.12, $R_{1}$ = 2.42$\pm$0.05, $R_2$ = 1.79$\pm$0.04, ($\odot$); $T_{1}$ $\sim$13000, $T_2$ $\sim$10600 (K); photometric distance $\sim$ 160 (pc). The high eccentricity and relatively short period (105 y) of apsidal revolution may be related to an apparent `slow B-type pulsator' (SPB) oscillation. Disturbances of the outer envelope of at least one of the components then compromise comparisons to standard evolutionary models, at least regarding the age of the system. A rate of apsidal advance is derived, which allows a check on the mean internal structure constant $\bar{k_2} = 0.0058 \pm 0.0004$. This is in agreement with values recently derived for young stars of solar composition and mass $\sim$3${\odot}$. For $\mu^1$ Sco, we agree with previous authors that the secondary component is considerably oversized for its mass, implying binary (interactive) stellar evolution, probably of the `Case A' type. The primary appears relatively little affected by this evolution, however. Its parameters show consistency with a star of its derived mass at age about 13 My, consistent with the star's membership of the Sco-Cen OB2 Association. The absolute parameters are as follows: $M_1$ = 8.3$\pm$1.0, $M_2$ = 4.6$\pm$1.0, $R_{1}$ = 3.9$\pm$0.3, $R_2$ = 4.6$\pm$0.4, ($\odot$); $T_{1}$ $\sim$24000, $T_2$ $\sim$17000 (K); photometric distance $\sim$ 135 (pc).