PU Vul Research Articles

An XMM-Newton View of the Symbiotic Stars HM Sge, NQ Gem, and PU Vul

We present the analysis of archival XMM-Newton observations of the symbiotic stars HM Sge, NQ Gem, and PU Vul. The EPIC-pn spectra hint at the presence of emission lines, which are further confirmed in the first-order RGS spectra of the three sources. Spectral modeling of the EPIC-pn data discloses unprecedented characteristics; for instance, the best fit to the EPIC-pn spectrum of the β-type symbiotic star PU Vul reveals the presence of two-plasma components. We report the discovery of an extremely soft spectral component in the EPIC-pn spectrum of the β-type symbiotic star HM Sge, which we suggest is produced by periodic mass ejections such as jets. Consequently, we suggest that a simple β-type classification no longer applies to HM Sge. Finally, the spectrum of the β/δ-type symbiotic star NQ Gem cannot be fitted by a two-temperature plasma model as performed by previous authors. The model requires extra components to fit the 1.0–4.0 keV energy range. More sophisticated models to β/δ-type symbiotic stars are needed in order to peer into the accretion process from such systems.

Spectroscopic and photometric observations of symbiotic nova PU Vul during 2009–2016

A new set of low-resolution spectral and UBVJHKL-photometric observations of the symbiotic nova PU Vul is presented. The binary has been evolving after its symbiotic nova outburst in 1977 and now it is in the nebular stage. It is found that the third orbital cycle (after 1977) was characterized by great changes in associated light curves. Now, PU Vul exhibits a sine-wave shape in all the light curves (with an amplitude in the U band of about 0.7 mag), which is typical for symbiotic stars in the quiescent state. Brightness variability due to pulsations of the cool component is now clearly visible in the VRI light curves. The amplitude of the pulsations increases from 0.5 mag in the V band to 0.8 mag in the I band. These two types of variability, as well as a very slow change in the physical parameters of the hot component due to evolution after the outburst of 1977, influence the spectral energy distribution (SED) of the system. The variability of emission lines is highly complex. Only hydrogen line fluxes vary with orbital phase. An important feature of the third orbital cycle is the first emergence of the OVI, 6828Å Raman scattering line. We determine the temperature of the hot component by means of the Zanstra method applied to the He II, 4686Å line. Our estimate is about 150 000 K for the spectrum obtained near orbital maximum in 2014. The VO spectral index derived near pulsation minimum corresponds to M6 spectral class for the cool component of PU Vul.

An illumination effect and an eccentric orbit for the symbiotic binary PU Vul revealed by 32 years of optical spectroscopy

We analyze $\sim$32 years of optical spectra and photometry for the symbiotic binary PU Vul. Light curves for the He I $\lambda$4471, He II $\lambda$4686 and H$\beta$ $\lambda$4861 emission lines reveal an illumination effect, where the hot white dwarf ionizes the outflowing wind of the red giant, and evidence for an eccentric orbit with e $\approx$ 0.16. Along with the gradual appearance of high ionization emission from [Fe VII] and O VI, the relative fluxes of these lines suggest an increase in the effective temperature of the hot component, from roughly $10^5$ K on JD 2448000 (1990) to roughly $2\times 10^5$ K on JD 2455000 (2009). During this period, the luminosity of the hot component dropped by a factor of 4$-$6 to a current value of roughly 1000 L$_{\odot}$.

Ultraviolet spectral variations of symbiotic nova PU Vul during and after second eclipse

I have analyzed spectral data of the symbiotic nova PU Vul observed with the International Ultraviolet Explorer (IUE) during the period 1993–1996. The study concentrated on the two sources of nebular emitting regions, the first is a nebula around the white dwarf partially eclipsed by a cool giant star and the second is a very extended nebular region not affected by the eclipse of the giant star. I concentrated on the N IV] 1486 A and C IV 1550 A emission lines produced in the first region and N III] 1750 A and C III] 1909 A emission lines produced in the second region very far from the giant star.

THE UBV COLOR EVOLUTION OF CLASSICAL NOVAE. II. COLOR–MAGNITUDE DIAGRAM

ABSTRACT We have examined the outburst tracks of 40 novae in the color–magnitude diagram (intrinsic B − V color versus absolute V magnitude). After reaching the optical maximum, each nova generally evolves toward blue from the upper right to the lower left and then turns back toward the right. The 40 tracks are categorized into one of six templates: very fast nova V1500 Cyg; fast novae V1668 Cyg, V1974 Cyg, and LV Vul; moderately fast nova FH Ser; and very slow nova PU Vul. These templates are located from the left (blue) to the right (red) in this order, depending on the envelope mass and nova speed class. A bluer nova has a less massive envelope and faster nova speed class. In novae with multiple peaks, the track of the first decay is more red than that of the second (or third) decay, because a large part of the envelope mass had already been ejected during the first peak. Thus, our newly obtained tracks in the color–magnitude diagram provide useful information to understand the physics of classical novae. We also found that the absolute magnitude at the beginning of the nebular phase is almost similar among various novae. We are able to determine the absolute magnitude (or distance modulus) by fitting the track of a target nova to the same classification of a nova with a known distance. This method for determining nova distance has been applied to some recurrent novae, and their distances have been recalculated.

Symbiotic Nova PU Vul - 33 Years of Observations

Abstract We present UBVRI light curves of the symbiotic nova PU Vul after its outburst in 1978. Three observed eclipses of the hot component by the cool one were used to determine the ephemeris of the binary system as JD (Min I) = 2444550(15) + 4897(10) × E days. the 194-day shift of the secondary minimum from its expected positions in 2001 suggests the eccentricity of the binary orbit. Period analysis of the VRI photometry improved the pulsation period of the cool AGB variable in the system to P = 217.7 days. Pulsation of the cool component is detected only in the phases around the primary minimum, when the visible hemisphere of the AGB star is not influenced by the interaction with the hot component.

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.

EFFECTS OF A COMPANION STAR ON SLOW NOVA OUTBURSTS—TRANSITION FROM STATIC TO WIND EVOLUTIONS

Two types of nova evolutions can be realized in low mass white dwarfs of ~0.5-0.7 M_sun, i.e., an evolution with optically thick winds like in usual classical novae, or an another type of evolution without them like in the symbiotic nova PU Vul. The latter type is characterized by spectra of no indication of strong winds as well as a long-lasted flat optical peak in its light curve. We propose a transition from no-optically-thick-wind evolution to usual evolution with optically thick winds as a new outburst model for slow novae that show a relatively long-lasted multipeak phase followed by a wind phase like in the slow novae V723 Cas, HR Del, and V5558 Sgr. We calculated nova envelopes with one-dimensional approximation of the companion's effects and found that when the companion star is deeply embedded in the extended nova envelope, the structure of static envelope approaches that of the optically thick wind solution. Thus, the transition from static to wind solution is triggered by the effect of the companion. The transition occurs in a close binary nova like V723 Cas, but is not triggered in a long period binary like PU Vul. We reconfirm our previous results that the frictional energy deposition is negligibly small in almost all of hydrogen/helium novae because of the low envelope density at the orbit.

Spectroscopy and photometry of the symbiotic nova PU Vul during its nebular phase and minimum of 2007

We present the results of our analysis of the spectrophotometric and photometric data for the symbiotic nova PU Vul acquired in 2001–2008. The continuum in the optical observed in 2006–2008 cannot be reconciled with a standard model including light from the cool component, hot component, and nebula. The hot component’s temperature increased to 194 000 K by 2008, while its luminosity decreased by a factor of ten compared to the plateau of 1979–1991. The evolution of the hot component as reflected by the Hertzsprung-Russell diagram does not agree with a theoretical model describing the evolution of a thermonuclear outburst in a white-dwarf envelope. We estimate the mass of the hot component to be 0.5M ⊙ based on the luminosity of the hot component during the plateau stage. Our spectroscopy reveals periodic continuum-flux variations due to brightness variability of the cool component, with an amplitude of at least 2 m at 7000 A. The spectral type of the cool component in 2008 was M6.3.

A LIGHT-CURVE MODEL OF THE SYMBIOTIC NOVA PU Vul (1979): A VERY QUIET EXPLOSION WITH LONG-LASTING FLAT PEAK

We present a light curve model of the symbiotic nova PU Vul (Nova Vulpeculae 1979) that shows a long-lasted flat peak with no spectral indication of wind mass-loss before decline. Our quasi-evolution models consisting of a series of static solutions explain both the optical flat peak and ultraviolet (UV) light curve simultaneously. The white dwarf mass is estimated to be ~0.6 Mo. We also provide a new determination of the reddening, E(B-V) = 0.43 +/- 0.05, from UV spectral analysis. Theoretical light curve fitting of UV 1455 A provides the distance of d=3.8 +/- 0.7 kpc.

Symbiotic Stars on Asiago Archive Plates

ABSTRACTThe Asiago photographic archive has been searched for plates containing the symbiotic stars AS 210, AS 327, AX Per, BF Cyg, CI Cyg, DT Ser, EG And, GH Gem, Hen 2-442, Hen 3-1591, HM Sge, MaC 1-17, NSV 11776, Pe 2-16, Pt 1, PU Vul, RS Oph, T CrB, UV Aur, V1016 Cyg, V1329 Cyg, V352 Aql, V4018 Sgr, Wray 15-1470, and Z And. A total of 1617 good-quality plates imaging the program stars have been found and their brightness has been estimated using the Henden & Munari UBVRC IC local photometric sequences. The results for the objects with most abundant measurements are discussed.

Analysis of archive UV observations of the symbiotic nova PU Vul during its nebular stage and brightness minimum in 1993–1994

We present an analysis of the poorly studied UV spectra of the symbiotic Nova PU Vul taken in 1991–1996. The continuum spectral energy distribution during that period (the nebular phase) can be reproduced by the standard model, which includes radiation from the hot component and nebula, in contrast to spectra observed in the 1980s, when the hot component of PU Vul was in its “supergiant” stage. The hot component’s temperature gradually increased from74 000 K (1991) to 100 000 K (1996), and the evolution of this component reflected by the Hertzsprung-Russell diagram corresponds to theoretical models describing the evolution of a thermonuclear outburst in the envelope of a white dwarf. Based on our analysis of UV observations of the eclipse in 1993–1994, we estimate the size of the cool component to have been at least 285R⊙. This confirms earlier suggestions that the cool component of PU Vul belongs to luminosity class II (bright giants) or I (supergiants), rather than class III (normal giants). Our analysis of Rayleigh scattering of the hot component’s radiation on atomic hydrogen in the extended atmosphere of the cool component suggests that the mass-loss rate of the cool component of PU Vul is variable.

MULTIPLICITY OF NOVA ENVELOPE SOLUTIONS AND OCCURRENCE OF OPTICALLY THICK WINDS

We revisit the occurrence condition of optically thick winds reported by Kato in 1985 and Kato and Hachisu in 1989 who mathematically examined nova envelope solutions with an old opacity and found that optically thick winds are accelerated only in massive white dwarfs (WDs) of 0.9 M ☉. With the OPAL opacity we find that the optically thick wind occurs for 0.6 M ☉ WDs and that the occurrence of winds depends not only on the WD mass but also on the ignition mass. When the ignition mass is larger than a critical value, winds are suppressed by a density-inversion layer. Such a static solution can be realized in WDs of mass ~0.6-0.7 M ☉. We propose that sequences consisting only of static solutions correspond to slow evolutions in symbiotic novae like PU Vul because PU Vul shows no indication of strong winds in a long-lasted flat peak followed by a very slow decline in its light curve.

NEBULAR SPECTRUM OF PU VUL IN 2004

A high resolution spectrum of PU Vul obtained at Bohyunsan Astronomy Observatory on April 9, 2004 is presented. At this phase, PU Vul was an emission-line star and its continuum was very weak. Emission lines of He II, H I, [Ne IV], [N II], [O III], [Ar V ] and [Fe VII] dominated the spectrum of PU Vul. Many of them exhibited hat-top profiles with strong and multi-peaked emissions on flat-tops of their profiles. Radial velocities for these lines were measured. Origins of the spectral lines are discussed in terms of the wind and the photoionization models.

2004년 PU VUL의 고분산 스펙트럼 - I

We present a high resolution spectrum of PU Vul observed at Bohyunsan Optical Astronomy Observatory (BOAO) on April 9, 2004. Permitted emission and nebular lines of PU Vul had been significantly changed compared to all spectra observed since its eruption in 1979. Therefore all new lines should be re-identified and were done so. We do-convoluted a <TEX>$H{\beta}$</TEX> line into several emission components with Gaussian functions. Then we carefully discussed the geometrical feature of PU Vul in April 2004.

Long-Term Photometry of Very Slow Novae

Abstract Long-term photographic, photoelectric and recent CCD photometry of the classical nova V723 Cas and symbiotic novae V1329 Cyg, PU Vul, V1016 Cyg and HM Sge were used to find their orbital periods. The arguments in favor of the presence of the third components in these systems are given. Physical processes, responsible for the brightness variations, are discussed.

HST/WFPC2 snapshot imaging of symbiotic stars

The results of a HST/WFPC2 snapshot imaging survey of selected symbiotic stars in 1999/2000 are presented. Seven sources - HD 149427 (PC 11), PU Vul, RT Ser, He2-104 (Southern Crab), V1329 Cyg (HBV 475), V417 Cen, AS 201 - were observed in filters F218W (ultraviolet continuum), F502N ([OIII]lambda 4959,5007) and F656N (Halpha); an eighth source, RS Oph, was observed in F437N ([OIII]lambda 4363), F502N and F656N. The presence of extended emission was detected in He2-104, V1329 Cyg and possibly HD 149427. In He2-104 we detected the [OIII] and Halpha counterparts to the inner lobes found in [NII] by Corradi et al. For V1329 Cyg, comparison with previously published HST/FOC results indicates expanding ejecta which may be associated with an ejection event in 1982 (+/-2 years) at a velocity of 260 +/- 50 km/s in the plane of the sky and at an assumed distance of 3.4kpc. We also present previously unpublished radio images of HD 149427, which we have obtained from the archives of the Australia Telescope Compact Array and which reveal the presence of extended emission at a similar orientation to that of the possible optical extension. Finally we also include HST/WFPC2 GO observations of AG Peg and detect possible extended emission in the F218W filter.

Photometric Oscillations at about 200 Days in the Symbiotic Variable PU Vulpeculae

ABSTRACTWe show that as PU Vul fell to full quiescence in 1994, following a long outburst, the system developed well‐defined 0.2 mag oscillations with a characteristic period of ∼211 days. This quasi‐periodicity is distinctly different from the behavior seen during late decline from outburst, where weaker photometric variations near 317, 227, and 120 days were seen. Suggested causes for this variation are discussed.

Pulsation of the AGB Variable in the Symbiotic Nova PU Vulpeculae

AbstractAnalysis of the 1993–4 eclipse in the slow symbiotic nova PU Vul (4900-d binary orbital period) and 1995-9 photoelectric observations in V and R bandpasses show that the cool component of this object is pulsating AGB variable with a 215-d pulsation period. Basic properties of the components of the system are discussed.

Near‐Infrared and Ultraviolet Spectrophotometry of Symbiotic Novae

In this paper we present an atlas of near-infrared spectrophotometry of symbiotic novae and report results from nearly contemporaneous IUE observations. The data cover RT Ser, AG Peg, V1016 Cyg, V1329 Cyg, HM Sge, and Pu Vul, most of the known symbiotic novae that are observable from the northern hemisphere. Emission-line strengths for both spectral regions are tabulated. Extinction values are derived from He II λ1640 in the UV and He II λ10124 in the infrared. Spectral types are determined for the cool giant component using infrared absorption features. The extinction and apparent J (1.25 μm) magnitude measured from the spectrophotometry are combined with the known relation between spectral type and absolute magnitude to derive distances for each system.