High-speed photometry and spectroscopy of the dwarf nova TY Piscis Austrini

High-speed photometry of the SU UMa type dwarf nova TY PsA (PS 74) has been obtained during quiescence and in both a normal and a superoutburst. Simultaneous spectroscopy was acquired on four nights of the superoutburst. An orbital period $$P_\text {orb} = 0.08400\pm 0.00006$$ day and a superhump period P_s = 0.08765 day are derived from the photometry. An apparent shallow eclipse appears on the decline from supermaximum (as already noted by Barwig et al.) but is not present at quiescence. During the superoutburst the spectra show broad absorption lines with central emission cores. The cores are narrower than at quiescence but the total emission in the lines does not vary noticeably between quiescence and outburst. The absorption lines are strongly asymmetric, with the asymmetry changing in sign on the 2-day beat cycle between P_orb and P_s. This accounts for the + 400 to – 200 km s⁻¹ daily swing in systemic velocity. We propose that these spectroscopic properties are most readily explained if TY PsA develops a non-axially symmetric accretion disc during superoutbursts. On two nights, deep and narrow absorption lines were present for a few minutes. These are similar to those seen throughout the orbital cycle of the higher inclination system Z Cha. We suggest that TY PsA has an inclination such that occasionally cool gas lying above the accretion disc is seen projected against the bright centre of the disc. Despite adequate spectroscopic coverage, no radial velocity variations at the orbital period are detectable during outburst to a velocity limit of $$K_1\leqslant 8\enspace\text {km s}^{-1}$$. As other evidence indicates that TY PsA is not of very low inclination, this implies an apparent upper limit $$\sim 0.02 M_\odot$$ for the mass of the secondary. On four nights during the superoutburst, and on one night of the ordinary outburst, rapid oscillations with periods in the range 25–30 s were observed. The unusually large amplitudes of these oscillations allow a more detailed investigation of the phase and amplitude variations than has hitherto been possible for dwarf nova oscillations. The results are very similar to what has been observed by Cordova et al. in the soft X-rays from SS Cyg.