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Keywords:

  • binaries: eclipsing;
  • stars: early-type;
  • stars: emission-line, Be;
  • stars: evolution;
  • stars: mass-loss;
  • stars: winds, outflows

ABSTRACT

V 393 Scorpii is a double periodic variable characterized by a relatively stable non-orbital photometric cycle of 253 d. Mennickent et al. argue for the presence of a massive optically thick disc around the more massive B-type component and describe the evolutionary stage of the system. In this paper, we analyse the behaviour of the main spectroscopic optical lines during the long non-orbital photometric cycle. We study the radial velocity of the donor determining its orbital elements and find a small but significant orbital eccentricity (e = 0.04). The donor spectral features are modelled and removed from the spectrum at every observing epoch using the light-curve model given by Mennickent et al. We find that the line emission is larger during eclipses and mostly comes from a bipolar wind. We also find that the long cycle is explained in terms of a modulation of the wind strength; the wind has a larger line and continuum emissivity at the high state. We report the discovery of highly variable chromospheric emission in the donor, as revealed by the Doppler maps of the emission lines Mg ii 4481 and C i 6588. We discuss notable and some novel spectroscopic features like discrete absorption components, especially visible at blue depressed O i 7773 absorption wings during the second half-cycle, Balmer double emission with V/R curves showing ‘Z-type’ and ‘S-type’ excursions around secondary and main eclipses, respectively, and Hβ emission wings extending up to ± 2000 km s−1. We also discuss possible causes for these phenomena and for their modulations with the long cycle.