Context : To add to the growing collection of well-studied double periodic variables ( DPVs ) we have carried out the first spectroscopic and photometric analysis of the eclipsing binary DQ Velorum to obtain its main physical stellar and orbital parameters .

Aims : Combining spectroscopic and photometric observations that cover several orbital cycles allows us to estimate the stellar properties of the binary components and the orbital parameters .
We also searched for circumstellar material around the more massive star .

Methods : We separated DQ Velorum composite spectra and measured radial velocities with an iterative method for double spectroscopic binaries .
We obtained the radial velocity curves and calculated the spectroscopic mass ratio .
We compared our single-lined spectra with a grid of synthetic spectra and estimated the temperature of the stars .
We modeled the V-band light curve with a fitting method based on the simplex algorithm , which includes an accretion disc .
To constrain the main stellar parameters we fixed the mass ratio and donor temperature to the values obtained by our spectroscopic analysis .

Results : We obtain a spectroscopic mass ratio q = 0.31 \pm 0.03 together with donor and gainer masses M _ { \mathrm { d } } = 2.2 \pm 0.2 M _ { \odot } , M _ { \mathrm { g } } = 7.3 \pm 0.3 M _ { \odot } , the radii R _ { \mathrm { d } } = 8.4 \pm 0.2 R _ { \odot } , R _ { \mathrm { g } } = 3.6 \pm 0.2 R _ { \odot } and temperatures T _ { \mathrm { d } } = 9400 \pm 100 \mathrm { K } , T _ { g } = 18 500 \pm 500 \mathrm { K } for the stellar components .
We find that DQ Vel is a semi-detached system consisting of a B3V gainer and an A1III donor star plus an extended accretion disc around the gainer .
The disc is filling 89 \% of the gainer Roche lobe with a temperature of 6580 \pm 300 \mathrm { K } at the outer radius .
It has a concave shape that is thicker at its edge ( d _ { \mathrm { e } } = 0.6 \pm 0.1 R _ { \odot } ) than at its centre ( d _ { \mathrm { c } } = 0.3 \pm 0.1 R _ { \odot } ) .
We find a significant sub-orbital frequency of 0.19 d ^ { -1 } in the residuals of the V-band light curve , which we interpret as a pulsation of an slowly pulsating B-type ( SPB ) of a gainer star .
We also estimate the distance to the binary ( d \sim 3.1 \mathrm { kpc } ) using the absolute radii , apparent magnitudes , and effective temperatures of the components found in our study .

Conclusions :