Evolution of the Symbiotic Nova PU Vul -- Outbursting White Dwarf, Nebulae, and Pulsating Red Giant Companion

We present a composite light-curve model of the symbiotic nova PU Vul (Nova Vulpeculae 1979) that shows a long-lasted flat optical peak followed by a slow decline. Our model light-curve consists of three components of emission, i.e., an outbursting white dwarf (WD), its M-giant companion, and nebulae. The WD component dominates in the flat peak while the nebulae dominate after the photospheric temperature of the WD rises to log T (K) >~ 4.5, suggesting its WD origin. We analyze the 1980 and 1994 eclipses to be total eclipses of the WD occulted by the pulsating M-giant companion with two sources of the nebular emission; one is an unocculted nebula of the M-giant's cool-wind origin and the other is a partially occulted nebula associated to the WD. We confirmed our theoretical outburst model of PU Vul by new observational estimates, that spanned 32 yr, of the temperature and radius. Also our eclipse analysis confirmed that the WD photosphere decreased by two orders of magnitude between the 1980 and 1994 eclipses. We obtain the reddening E(B-V) ~ 0.3 and distance to PU Vul d ~ 4.7 kpc. We interpret the recent recovery of brightness in terms of eclipse of the hot nebula surrounding the WD, suggesting that hydrogen burning is still going on. To detect supersoft X-rays, we recommend X-ray observations around June 2014 when absorption by neutral hydrogen is minimum.Comment: 16 pages including 8 figs, to appear in Ap

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.Comment: 8 pages, 6 figures, 2 tables, New Astron. in pres

The Continuing Slow Decline of AG Pegasi

We analyze optical and ultraviolet observations of the symbiotic binary AG Pegasi acquired during 1992-97. The bolometric luminosity of the hot component declined by a factor of 2-3 from 1980-1985 to 1997. Since 1992, the effective temperature of the hot component may have declined by 10%-20%, but this decline is comparable to the measurement errors. Optical observations of H-beta and He I emission show a clear illumination effect, where high energy photons from the hot component ionize the outer atmosphere of the red giant. Simple illumination models generally account for the magnitude of the optical and ultraviolet emission line fluxes. High ionization emission lines - [Ne V], [Mg V], and [Fe VII] - suggest mechanical heating in the outer portions of the photoionized red giant wind. This emission probably originates in a low density region $\sim$ 30-300 AU from the central binary.Comment: 17 pages, 7 pages, 5 tables; to be published in the Astronomical Journal, July 200

The remarkable properties of the symbiotic star AE Circinus

We present new optical spectroscopy and photometry, 2MASS infrared observations and 24 years of combined AAVSO and AFOEV photometry of the symbiotic star candidate \ae. The long-term light curve is characterized by outbursts lasting several years and having a slow decline of $\sim 2 \times 10^{-4}$ mag/day. The whole range of variability of the star in the $V$ band is about 4 magnitudes. The periodogram of the photometric data reveals strong signals at $\sim$ 342 and 171 days. The presence of the emission feature at $\lambda$ 6830 \AA at minimum and the detection of absorption lines of a $\sim$ K5 type star confirm the symbiotic classification and suggest that AE Cir is a new member of the small group of s-type yellow symbiotic stars. We estimate a distance of 9.4 kpc. Our spectrum taken at the high state shows a much flatter spectral energy distribution, the disappearance of the $\lambda$ 6830 \AA emission feature and the weakness of the He II 4686 emission relative to the Balmer emission lines. Our observations indicate the presence of emission line flickering in time scales of minutes in 2001. The peculiar character of \ae is revealed in the visibility of the secondary star at the high and low state, the light curve resembling a dwarf nova superoutburst and the relatively short low states. The data are hard to reconciliate with standard models for symbiotic star outbursts.Comment: accepted for publication in MNRAS, 7 figure

The historical light curve of the symbiotic star AG Draconis: intense, magnetically induced cyclic activity

We analyze an optical light curve of the symbiotic system AG Draconis covering the last 120 years of its history. During the first 32 years the system was in a quiescence state. Around the year 1922 the star's quiescence luminosity brightened by 0.29 mag. The last 82 years of the light curve (LC) are characterized by a series of outbursts of 1-2 magnitude in brightness and about 100 days in duration. The outbursts are distributed along the time axis in 6 clusters with a quasi-periodic cycle of some 5300 days. The time intervals among the outbursts themselves are integral numbers of the period 373.5 days. During quiescence states the LC oscillates with the binary period of the system of 550 d. The LC contains also a weak periodic signal with a period of 350 d, attributed to pulsations of the giant star. Another period of 1160 d is also present in the light curve, being the sidereal rotation period of the giant star. We suggest that the outbursts are events of intense mass transfer from the giant onto the hot component. These are modulated by an interplay between a solar-like magnetic dynamo cycle operating in the outer layers of the giant, and a tidal deformation of these layers that circulates the surface of the giant with the synodic diurnal period of 373.5 Earth days. AG Dra is the 5th symbiotic system with a light curve that reflects such an intense magnetic and magnetically modulated activity. (Abridged)Comment: 10 pages, 4 figures. Accepted for publication in MNRA

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.Comment: 18 pages (printed format), 9 figures, 4 tables, 2 appendices; accepted for publication in A&A (02/03/2006

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.Comment: 37 pages in printed format, 27 figures, 4 tables, accepted for publication in Astronomy and Astrophysic