The hot and cool component of the symbiotic nova SMC 3^*

A supersoft X-ray variable and a small-amplitude red variable

Sternwarte Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany

Corresponding author: pkahabka@astro.uni-bonn.de

Received: 9 December 2002
Accepted: 26 November 2003

Abstract

The ~6 year supersoft X-ray lightcurve of the symbiotic nova SMC 3 (=RX J0048.4-7332) in the Small Magellanic Cloud is derived from archival ROSAT PSPC and HRI data. It shows one deep X-ray eclipse during which the count rate decreased by a factor of 80. In MACHO B-band data sinusoidal variation is found with a quasi-periodicity of ~4 years. The minimum of the B-band flux occurs during the X-ray eclipse. In OGLE II I-band observations performed after the ROSAT observations we detect  day oscillations which we interpret as pulsations of the M0 giant star in the symbiotic system. The observed duration of the supersoft X-ray eclipse of ~0.4–1.8 years is explained by the occultation of the white dwarf by the giant companion with an orbital period of ~(4.0–4.8) years and a strong wind blown from its surface with a mass loss rate of ~, assuming that ~ of the ionized phase is neutral (e.g. due to dust) and assuming a terminal velocity of ~. The ~4 year quasi-periodicity found in the optical is explained as the binary orbital period of the system. It is less likely that it reflects the activity (or mass-loss) time scale of the red giant star. A ~(700–800) day quasi-periodicity found in the OGLE II and MACHO data is explained as the first harmonic of a binary orbital cycle. SMC 3 therefore may be classified as a small-amplitude red variable star (SARV). The hot star most likely is in a state of steady nuclear burning with an accretion rate somewhat below the upper critical value of ~.