The hot and cool component of the symbiotic nova SMC 3

Free access article

Issue		A&A Volume 416, Number 1, March II 2004


Page(s)		57 - 65
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20031290

A&A 416, 57-65 (2004)
DOI: 10.1051/0004-6361:20031290

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

P. Kahabka

Sternwarte Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
(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 $\ga$ 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 $110\pm2$ 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 ~ $(2.6{-}8.2)\times 10 ^{-7}\ {M}_{\odot}\ {\rm yr^{-1}}$ , assuming that ~ $(1{-}3.5)\%$ of the ionized phase is neutral (e.g. due to dust) and assuming a terminal velocity of ~ $30\ {\rm km}\ {\rm s^{-1}}$ . 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 ~ $10^{-7}\ {M}_{\odot}\ {\rm yr}^{-1}$ .

Key words: galaxies: Magellanic Clouds -- stars: binaries: symbiotic -- stars: individual: RX J0048.4-7332 (=SMC 3) -- stars: mass-loss -- X-rays: stars

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