Formation of a disk structure in the symbiotic binary AX Persei during its 2007–10 precursor-type activity

Abstract

Context. AX Per is an eclipsing symbiotic binary. During active phases, deep narrow minima are observed in its light curve, and the ionization structure in the binary changes significantly. From ∼2007.5, AX Per entered a new active phase. Aims. We aim to derive the ionization structure in the binary and its changes during the recent active phase. Methods. We used optical high-and low-resolution spectroscopy and UBVR C I C photometry. We modeled the SED in the optical and broad wings of the Hα line profile during the 2007-10 higher level of the AX Per activity. Results. After 10 orbital cycles (∼18.6 years), we again measured the eclipse of the hot component by its giant companion in the light curve. We derived a radius of 27 ± 2 R for the eclipsed object and 115 ± 2 R for the eclipsing cool giant. The new active phase was connected with a significant enhancement of the hot star wind. From quiescence to activity, the mass-loss rate increased from ∼9 × 10 −8 to ∼3 × 10 −6 M yr −1 , respectively. The wind causes the emission of the He ++ zone, located in the vicinity of the hot star, and also is the reason for the fraction of the [O iii] zone at farther distances. Simultaneously, we identified a variable optically thick warm (T eff ∼ 6000 K) source that contributes markedly to the composite spectrum. The source was located at the hot star's equator and has the form of a flared disk, whose outer rim simulates the warm photosphere. Conclusions. The formation of the neutral disk-like zone around the accretor during the active phase was connected with its enhanced wind. It is probable that this connection represents a common origin of the warm pseudophotospheres that are indicated during the active phases of symbiotic stars.

Ionization structure of hot components in symbiotic binaries during active phases

“…The model is also consistent with the ionization structure derived from the photometric and spectroscopic analysis of the eclipsing symbiotic binary AX Per during its recent active phase (see Fig. 9 of Skopal et al 2011). …”

“…L = 2700 ± 700 L and L H = (1.4 ± 0.4) × 10 47 s −1 ), as representative values for the active A21, page 6 of 10 phases of AG Dra, Z And, AX Per, AE Ara, and AR Pav. The parameters v ∞ andṀ for these systems are available in Table 1 of Skopal (2006) and Table 7 of Skopal et al (2011). The X(Ṁ) quantities of active symbiotic stars lie well within the possibility of creation of the flared neutral disk-like zone predicted by the WCZ model (the grey belt in Fig.…”

“…1 there), which for A = 419 R (Schild et al 2001) implies R d = 21±8 R . AX Per: recently, Skopal et al (2011) derived R d = 27 ± 2 R from the 2009 eclipse, which developed during the 2007−10 active phase. The eclipse profile was asymmetric, with the first two contact times corresponding to R d = 22.3 ± 2 R , in particular agreement with the disk radius derived from the model SED (R eff h = 11 R and Eq.…”

“…6). For a canonical value of H/R d ≡ 0.3 during active phases Table 4 of Skopal (2005) and Table 8 of Skopal et al (2011).…”

Recent photometry of symbiotic stars

“…The main change in the LC profile, covered by our new observations, happened at ∼2007.5, when the broad wave-like minimum transformed into a narrow minimum placed at the inferior conjunction of the giant (Fig. 16 here; Skopal et al 2011). This sudden and significant change in the minimum profile reflects a strong change in the ionization structure of the binary as a consequence of a new active phase.…”