Spiral waves and the secondary star in the nova-like variable V3885 Sgr

Abstract

We present seven nights’ blue (4300–5000u spectroscopy of the novalike variable star, V3885 Sgr. The line spectrum shows a typical combination of broad absorption and emission in H γ and H β and He i, which is associated with the accretion disk. We also observe anti-phased narrow emission, which we attribute to irradiation of the secondary star. The He ii λ4686 and N iii–C iii–C iv emission lines are devoid of structure and are most likely formed in an outflow. We measure radial velocity shifts in the absorption and emission lines, from which we fit an orbital period of 4.97126± 0.00036h. From the velocity semi-amplitudes of the disk and companion star, we are able to constrain the binary mass ratio to q > 0.7. The phase-folded spectra provide dense coverage of the entire orbital cycle. Doppler tomograms of the hydrogen and He i lines reveal spiral structure in the accretion disk and the irradiated donor star. We believe this is the first unambiguous detection of spiral waves in a novalike variable.