Search

We investigate the luminous star ELHC 10 located in the bar of the Large Magellanic Cloud (LMC), concluding that it is a SB1 long-period eclipsing binary where the main eclipse is produced by an opaque structure hiding the secondary star. For the more luminous component we determine an effective temperature of 6500±250 K, log g=1.0±0.5 and luminosity 5970 L⊙. From the radial velocities of their photospheric lines, we calculate a mass function of 7.37 ± 0.55 M⊙. Besides Balmer and forbidden NII emission, we find splitting of metallic lines, characterized by strong discrete absorption components, alternatively seen at the blue and red side of the photospheric spectrum. These observations hardly can be interpreted in terms of an structured atmosphere but might reflect mass streams in an interacting binary. The primary shows signatures of s-process nucleosynthesis and might be a low-mass post-asymptotic giant branch star with a rare evolutionary past if the binary is semidetached. The peak separation and constancy of radial velocity in Hα suggest that most of the Balmer emission comes from a circumbinary disc. [ABSTRACT FROM AUTHOR]

We analyse multicolour light curves and high-resolution optical spectroscopy of the eclipsing binary and double periodic variable (DPV) OGLE 05155332−6925581. According to Mennickent et al., this system shows a significant change in the long non-orbital photometric cycle, a loop in the colour–magnitude diagram during this cycle and discrete spectral absorption components that were interpreted as evidence of systemic mass loss. We find that the best fit to the multiband light curves requires a circumprimary optically thick disc with a radius about twice the radius of the more massive star. The spectroscopy indicates a mass ratio of 0.21 ± 0.02 and masses for the hot and cool stars of 9.1 ± 0.5 and 1.9 ± 0.2 M⊙, respectively. A comparison with synthetic binary-star evolutionary models indicates that the system has an age of 4.76 × 107 yr, and is in the phase of rapid mass transfer, the second one in the life of this binary, in a Case-B mass-exchange stage. Donor-subtracted Hα profiles show the presence of double emission formed probably in an optically thin circumstellar medium, while the variable He i profile and the Hβ absorption wings are probably formed in the optically thick circumprimary disc. The model that best fits the observations shows the system with a relatively large mass transfer rate of $\dot{M}$ = 3.1 × 10−6 M⊙ yr−1. However, the orbital period remains relatively stable during almost 15 yr. This observation suggests that the hotspot mass-loss model proposed by other authors is not adequate in this case, and that some other mechanism is efficiently removing angular momentum from the binary. Furthermore, our observations suggest that the DPV phenomenon could have an important effect in the balance of mass and angular momentum in the system. [ABSTRACT FROM PUBLISHER]