Fundamental parameters of the close interacting binary HD170582 and its luminous accretion disc

We present a spectroscopic and photometric study of the Double Period Variable HD170582. Based on the study of the ASAS V-band light curve we determine an improved orbital period of 16.87177 $pm$ 0.02084 days and a long period of 587 days. We disentangled the light curve into an orbital part, determining ephemerides and revealing orbital ellipsoidal variability with unequal maxima, and a long cycle, showing quasi-sinusoidal changes with amplitude $Delta V$= 0.1 mag. Assuming synchronous rotation for the cool stellar component and semi-detached configuration we find a cool evolved star of $M_{2}$ = 1.9 $pm$ 0.1 $M_{odot}$, $T_{2}$ = 8000 $pm$ 100 $K$ and $R_{2}$ = 15.6 $pm$ 0.2 $R_{odot}$, and an early B-type dwarf of $M_{1}$ = 9.0 $pm$ 0.2 $M_{odot}$. The B-type star is surrounded by a geometrically and optically thick accretion disc of radial extension 20.8 $pm$ 0.3 $R_{odot}$ contributing about 35% to the system luminosity at the $V$ band. Two extended regions located at opposite sides of the disc rim, and hotter than the disc by 67% and 46%, fit the light curve asymmetries. The system is seen under inclination 67.4 $pm$ 0.4 degree and it is found at a distance of 238 $pm$ 10 pc. Specially interesting is the double line nature of HeI 5875; two absorption components move in anti-phase during the orbital cycle; they can be associated with the shock regions revealed by the photometry. The radial velocity of one of the HeI 5875 components closely follows the donor radial velocity, suggesting that the line is formed in a wind emerging near the stream-disc interacting region.