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A. Skopal

Publications and source records attributed to A. Skopal.

30 records · Page 2Linked to original sources
arXiv2007

On the effect of emission lines on the UBVR photometry

We investigate the effect on the U, B, V, Rc and Rj magnitudes of the removal of emission lines from a spectrum. We determined "Dm" corrections from the ratio of fluxes with and without emission lines, transmitted from the object through the photometric filter. An exact and a simplified approach for operative use were applied. The effect was demonstrated for classical symbiotic stars, symbiotic novae and the classical nova V1974 Cyg. It was found that about 20-30, 30-40, 10 and 26/20 percents of the observed flux in the U, B, V and Rc/Rj filter, respectively, is radiated in the emission lines of the investigated classical symbiotic stars. The largest effect was found for symbiotic novae (RR Tel and V1016 Cyg) and the classical nova V1974 Cyg at 210 days (in average of 74, 79, 56 and 66/60 percents). Examples for practical application are suggested.

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arXiv2006

Broad H-alpha wings from the optically thin stellar wind of the hot components in symbiotic binaries

Aims: To model broad H-alpha wings observed in symbiotic binaries by an optically thin, bipolar stellar wind from their hot components as an alternative to that considering the Raman scattering of Ly-beta photons on atomic hydrogen. Methods: Profile-fitting analysis. Comparison of the observed broad H-alpha wings and their luminosity with those predicted by the model. Results: Synthetic H-alpha profiles fit excellently the observed wings for |RV| > 200 km/s in our sample of 10 symbiotic stars during the quiescent as well as active phases. The wing profile formed in the stellar wind can be approximated by a function f(RV) proportional to RVexp-2, which is of the same type as that arising from the Raman scattering. Therefore it is not possible to distinguish between these two processes only by modeling the line profile. Some observational characteristics of the H-alpha emission suggest the ionized stellar wind from the hot component to be the dominant source contributing to the H-alpha wings during active phases. The model corresponding mass-loss rates from the hot components are of a few x 10exp(-8) M(Sun)/yr and of a few x (10exp(-7) - 10exp(-6)) M(Sun)/yr during quiescent and active phases, respectively.

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arXiv2006

Structure of the hot object in the symbiotic prototype Z And during its 2000-03 active phase

Aims: To investigate structure of the hot object in the symbiotic prototype Z And during its major 2000-03 active phase. Methods: Analysis of the far ultraviolet, optical low- and high-resolution spectroscopy and UBVR photometry. Reconstruction of the spectral energy distribution (SED) during the outburst. The Raman scattering process. Results: At the initial stages of the outburst the hot object was characterized by the two-temperature spectrum (a warm stellar radiation and a strong nebular emission) with signatures of a mass-outflow at moderate (100-200 km/s) and very high (1000-2000 km/s) velocities. The corresponding structure of the hot object consists of an optically thick, slowly-expanding disk-like material encompassing the accretor at the orbital plane and a fast optically thin wind over the remainder of the star. A striking similarity of [FeVII]6087 and Raman 6825 profiles at/after the dilution of the disk suggested their origin within the interaction zone where the winds from the binary components collide.

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arXiv2005

Disentangling the composite continuum of symbiotic binaries I. S-type systems

We describe a method of disentangling the composite,0.12-5 microns continuum of symbiotic binaries.The observed SED is determined by the IUE/HST archival spectra and flux-points corresponding to the optical UBVRI and infrared JHKLM photometric measurements. The modeled SED is given by superposition of fluxes from the cool giant, hot stellar source and nebula including the effect of the Rayleigh scattering process and considering influence of the iron curtain absorptions.We applied this method to 21 S-type symbiotic stars during quiescence, activity and eclipses.

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arXiv2004

White dwarfs with jets as non-relativistic analogues of quasars and microquasars?

We explore the similarities between accreting white dwarfs (CH Cyg and MWC 560) and the much more energetic jet sources - quasars and microquasars. To-date we have identified several common attributes: (1) they exhibit collimated outflows (jets); (2) the jets are precessing; (3) these two symbiotic stars exhibit quasar-like emission line spectra; (4) there is a disk-jet connection like that observed in microquasars. Additionally they may have a similar energy source (extraction of rotational energy from the accreting object). Study of the low energy analogues could have important implications for our understanding of their higher energy cousins.

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arXiv2004

Correction of UBV photometry for emission lines

We investigated the effect on the U, B, V magnitudes of the removal of the emission lines from the spectra of some symbiotic stars and novae during their nebular phases. We approached this problem by a precise reconstruction of the composite UV/optical continuum and the line spectrum. Corrections DU, DB, DV are determined from the ratio of fluxes with and without emission lines. Here we demonstrate this effect on the case of the symbiotic nova V1016 Cyg during its nebular phase. We find that about 68, 78 and 66 per-cent of the observed flux in the U, B and V filters is radiated in the emission lines. The effect should be taken into account before using the observed color indices of emission-line objects for diagnosis of their radiation in the continumm.

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arXiv2003

Discovery of the eclipse in the symbiotic binary Z Andromedae

Our photometric observations of the symbiotic binary Z And during its recent (2000 -- 2003) active phase revealed a minimum in the U, B and V light curves (LC) at the position of the inferior conjunction of its cool component (the orbital phase 'phi' = 0). This fact and the behaviour of colour indices suggest that the minimum was due to the eclipse of the active hot object by the red giant. Physically plausible fit of the eclipse profile and a precise analysis of the spectral energy distribution (SED) in the ultraviolet continuum suggest a disk-like structure for the hot object during active phases. The present knowledge of fundamental parameters of the system limits the orbital inclination 'i' to 76 - 90 deg. The presence of the Rayleigh attenuated far-UV continuum at 'phi' around 0 during quiescent phase confirms the very high inclination of the Z And orbit.

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arXiv2003

The SED in the hot continuum of the symbiotic binary AR Pavonis. I. Tests with the current models

We present the spectral energy distribution (SED) in the continuum of the eclipsing symbiotic binary AR Pav between 0.12 and 3.4 microns. This revealed a high luminosity of the hot object in the binary, L(hot) = 2200(d/4.9 kpc)**2 L(Sun). We introduce a method of disentangling the total continuum spectrum into its individual components of radiation for current models of symbiotic binaries. Applying a standard ionization model we show that the configuration of AR Pav differs significantly from that typical for symbiotic binaries during their quiescent phases. The best fit of the observed SED is provided by radiation of a simple blackbody accretion disk with L(AD)=1700(d/4.9 kpc)**2 L(Sun), which is embedded in an extended hot corona with Te=40000+/-5000K and L(neb)=500 (d/4.9 kpc)**2 L(Sun). This basic configuration of the hot object explains also the observed wavelength-dependent depth and width of the eclipse profile. The standard thin disk model requires a high accretion rate dot M(acc) > 2x1E-4M(Sun)/yr onto the central star with a radius R(acc) > 2R(Sun) to balance the observed luminosity. Irrespectively to the disk model, the accretion process limits R(acc) > 0.1R(Sun) for dot M(acc) > 1.7x1E-5 M(Sun)/yr and M(acc)=0.75 - 1.0M(Sun), which precludes a white dwarf to be the accreting star. Application of models with the disk and the boundary layer shows that the far-UV spectrum is not consistent with a large amount of a hot radiation from the boundary layer.

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arXiv2002

The symbiotic star CH Cygni. III. A precessing radio jet

VLA, MERLIN and Hubble Space Telescope imaging observations of the extended regions of the symbiotic system CH Cygni are analysed. These extensions are evidence of a strong collimation mechanism, probably an accretion disk surrounding the hot component of the system. Over 16 years (between 1985 and 2001) the general trend is that these jets are seen to precess. Fitting a simple ballistic model of matter ejection to the geometry of the extended regions suggests a period of 6520 +/- 150 days, with a precession cone opening angle of 35 +/- 1 degrees. This period is of the same order as that proposed for the orbital period of the outer giant in the system, suggesting a possible link between the two. Anomalous knots in the emission, not explained by the simple model, are believed to be the result of older, slower moving ejecta, or possibly jet material that has become disrupted through sideways interaction with the surrounding medium.

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arXiv2001

The symbiotic star CH Cygni. I. Non-thermal bipolar jets

VLA surface brightness and spectral index maps of the evolving extended emission of the triple symbiotic star CH Cygni are presented. These are derived from observations at 4.8, 8.4 and 14GHz between 1985 and 1999. The maps are dominated by thermal emission around the central bright peak of the nebula, but we also find unambiguous non-thermal emission associated with the extended regions. Our observations confirm that this is a jet. The central region has been associated with the stellar components through HST imaging. If the jets are due to ejection events at outburst, expansion velocities are consistent with those from other measurement methods. We propose that the non-thermal emission is caused by material ejected in the bipolar jets interacting with the circumstellar wind envelope. The resulting shocks lead to local enhancements in the magnetic field from the compact component of the order 3mG.

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