arXiv subjects

Augustin Skopal

Publications and source records attributed to Augustin Skopal.

25 records · Page 2Linked to original sources

arXiv2012

Ionization structure of hot components in symbiotic binaries during active phases

During active phases of symbiotic binaries, an optically thick medium in the form of a flared disk develops around their hot stars. During quiescent phases, this structure is not evident. We propose the formation of a flared neutral disk-like structure around the rotating white dwarf (WD) in symbiotic binaries. We applied the wind compression model and calculated the ionization boundaries in the compressed wind from the WD using the equation of photoionization equilibrium. During active phases, the compression of the enhanced wind from the rotating WD can form a neutral disk-like zone at the equatorial plane, while the remainder of the sphere above/below the disk is ionized. Calculated hydrogen column density throughout the neutral zone and the emission measure of the ionized fraction of the wind are consistent with those derived from observations. During quiescent phases, the neutral disk-like structure cannot be created because of insufficient mass loss rate. Formation of the neutral disk-like zone at the equatorial plane is connected with the enhanced wind from the rotating WD, observed during active phases of symbiotic binaries. This probably represents a common origin of warm pseudophotospheres, indicated in the spectrum of active symbiotic binaries with a high orbital inclination.

astro-ph.SR↗

arXiv2011

Formation of neutral disk-like zone around the active hot stars in symbiotic binaries

In this contribution we present the ionization structure in the enhanced wind from the hot star in symbiotic binaries during active phases. Rotation of the hot star leads to the compression of the outflowing material towards its equatorial plane. As a result a neutral disk-like zone around the active hot star near the orbital plane is created. We modelled the compression of the wind using the wind compression model. Further, we calculated the neutral disk-like zone in the enhanced wind from the hot star using the equation of the photoionization equilibrium. The presence of such neutral disk-like zones was also suggested on the basis of the modelling the spectral energy distribution of symbiotic binaries. We confront the calculated ionization structures in the enhanced wind from the hot star with the observations. We found that the calculated column density of the neutral hydrogen atoms in the neutral disk-like zone and the emission measure of the ionized part of the wind from the hot star are in a good agreement with quantities derived from observations during active phases. The presence of such neutral disk-like zones is transient, being connected with the active phases of symbiotic binaries. During quiescent phases, such neutral disk-like zones cannot be created, because of insufficient mass loss rate of the hot star.

astro-ph.SR↗

arXiv2011

Creation of neutral disks during outbursts of symbiotic binaries

Multiwavelength modelling of the spectral energy distribution of symbiotic binaries suggests that a neutral disk-like zone is created around the hot star near the orbital plane during active phases. Presumably, this is connected with the enhanced wind from the active hot star. To test this idea, we applied the wind compression model to active hot stars in symbiotic binaries, within which the wind particles are compressed more to the equatorial plane due to a fast rotation of the hot star. Accordingly, we calculated the ionization structure for such compressed wind and ionizing photons from the hot star. We found that the hot star wind, enhanced during active phases to \sim (10^-7 - 10^-6) M_sun yr^-1, and the rotational velocity of 100 - 350 km s^-1 at the star's equator lead to formation of a neutral disk-shaped zone. The presence of such disks is transient, being connected with the active phases of symbiotic binaries. During quiescent phases, such neutral disks cannot be created, because of insufficient mass loss rate.

astro-ph.SR↗

arXiv2010

Notices to investigation of symbiotic binaries V. Physical parameters derived from UBV magnitudes

In the optical, the spectrum of symbiotic binaries consists of contributions from the cool giant, symbiotic nebula and the hot star. Strong emission lines are superposed on the continuum. In this paper we introduce a simple method to extract individual components of radiation from photometric UBV magnitudes. We applied the method to classical symbiotic stars AX Per, AG Dra, AG Peg and Z And, the symbiotic novae RR Tel and V1016 Cyg and the classical nova V1974 Cyg during its nebular phase. We estimated the electron temperature and emission measure of the nebula in these systems and the V magnitude of the giant in the symbiotic objects. Our results are in a good agreement with those obtained independently by a precious modelling the UV-IR SED.

astro-ph.SR↗

arXiv2008

How to understand the light curves of symbiotic stars

I introduce fundamental types of variations observed in the light curves (LC) of symbiotic stars: the orbitally-related wave-like modulation during quiescent phases, eclipses during active phases and apparent orbital changes indicated during transitions between quiescence and activity. I explain their nature with the aid of the spectral energy distribution (SED) of the composite spectrum of symbiotic stars and their simple ionization model.

astro-ph↗

arXiv2005

Light Variations of the Anomalous Central Star of Planetary Nebula Sh 2-71

We present an analysis of light variations in UBVRI of the anomalous object in the center of planetary nebula Sh 2-71. We refined the linear ephemeris of the light maxima to JD{max} = 2449862.0 + 68.101 (E-96), but also identified long-term, obviously non-periodic variations. The latter manifest themselves in large O-C shifts, a variable profile of light curves (hereafter LC) and changes in the mean brightness of the object. Our spectroscopic observations suggested the presence of a superdense nebula in the center of Sh 2-71.

astro-ph↗

arXiv2003

The role of ionization in symbiotic binaries

Processes of ionization and recombination often influence significantly the observed spectrum produced by symbiotic stars in a very wide wavelength region. Properties of the nebular spectrum provide important information on some fundamental parameters and on geometric structure of symbiotic stars. This paper reviews the recently recognized effects of ionization/recombination in these binaries and summarizes first results. We concentrate in this review on the continuum emission in the range from ultraviolet to near-IR wavelengths.

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