The Z Camelopardalis-type Star AY Piscium: Stellar and Accretion Disk Parameters

Abstract

We present a new study of the Z Cam-type eclipsing cataclysmic variable AY Piscium with the aim of determining the fundamental parameters of the system and the structure of the accretion flow therein. We use time-resolved photometric observations supplemented by spectroscopy in the standstill, to which we applied our light-curve modeling techniques and the Doppler tomography method, to update system parameters. We found that the system has a massive white dwarf M _WD = 0.90(4) M _☉ , a mass ratio q = 0.50(3), and the effective temperature of a secondary T _2 = 4100(50) K. The system inclination is i = 74.°8(7). The orbital period of the system P _orb = 0.217320523(8) day is continuously increasing at a rate of ${\dot{P}}_{\mathrm{orb}}=+7.6(5)\times {10}^{-9}$ day yr ^−1 . The mass-transfer rate varies between 2.4 × 10 ^−10 M _⊙ yr ^−1 in quiescence up to 1.36 × 10 ^−8 M _⊙ yr ^−1 in outburst. The accretion disk transitions from the cooler, flared, steady-state disk to a warmer state with a practically constant and relatively high disk height. The mass-transfer rate is about 1.6 × 10 ^−9 M _⊙ yr ^−1 in the standstill. The Balmer emission lines show a multicomponent structure similar to that observed in long-orbital-period nova-like systems. Out of standstill, the system exhibits outburst bimodality, with long outbursts being more prominent. We conclude that the Balmer emission lines in AY Psc are formed by the combination of radiation from the irradiated surface of the secondary, from the outflow zone, and from winds originating in the bright spot and the disk’s inner part.

Keywords

• Close binary stars
• Cataclysmic variable stars
• Dwarf novae
• Z Camelopardalis stars
• Fundamental parameters of stars
• Novae