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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Hydrodynamical Simulations of the Jet in the Symbiotic Star MWC 560: Application to X-ray Jets in Symbiotic Stars - 3

In Papers I and II in this series, we presented hydrodynamical simulations of jet models with parameters representative of the symbiotic system MWC 560. These were simulations of a pulsed, initially underdense jet in a high-density ambient medium. Since the pulsed emission of the jet creates internal shocks and since the jet velocity is very high, the jet bow shock and the internal shocks are heated to high temperatures and should therefore emit X-ray radiation. In this paper, we investigate in detail the X-ray properties of the jets in our models. We have focused our study on the total X-ray luminosity and its temporal variability, the resulting spectra, and the spatial distribution of the emission. Temperature and density maps from our hydrodynamical simulations with radiative cooling presented in the second paper are used, together with emissivities calculated with the atomic database ATOMDB. The jets in our models show extended and variable X-ray emission, which can be characterized as a sum of hot and warm components with temperatures that are consistent with observations of CH Cyg and R Aqr. The X-ray spectra of our model jets show emission-line features that correspond to observed features in the spectra of CH Cyg. The innermost parts of our pulsed jets show iron line emission in the 6.4-6.7 keV range, which may explain such emission from the central source in R Aqr. We conclude that MWC 560 should be detectable with Chandra or XMM-Newton, and such X-ray observations will prove crucial for understanding jets in symbiotic stars.

hydrodynamics↗
NASA NTRS1993

Models of symbiotic stars

One of the most important features of symbiotic stars is the coexistence of a cool spectral component that is apparently very similar to the spectrum of a cool giant, with at least one hot continuum, and emission lines from very different stages of ionization. The cool component dominates the infrared spectrum of S-type symbiotics; it tends to be veiled in this wavelength range by what appears to be excess emission in D-type symbiotics, this excess usually being attributed to circumstellar dust. The hot continuum (or continua) dominates the ultraviolet. X-rays have sometimes also been observed. Another important feature of symbiotic stars that needs to be explained is the variability. Different forms occur, some variability being periodic. This type of variability can, in a few cases, strongly suggest the presence of eclipses of a binary system. One of the most characteristic forms of variability is that characterizing the active phases. This basic form of variation is traditionally associated in the optical with the veiling of the cool spectrum and the disappearance of high-ionization emission lines, the latter progressively appearing (in classical cases, reappearing) later. Such spectral changes recall those of novae, but spectroscopic signatures of the high-ejection velocities observed for novae are not usually detected in symbiotic stars. However, the light curves of the 'symbiotic nova' subclass recall those of novae. We may also mention in this connection that radio observations (or, in a few cases, optical observations) of nebulae indicate ejection from symbiotic stars, with deviations from spherical symmetry. We shall give a historical overview of the proposed models for symbiotic stars and make a critical analysis in the light of the observations of symbiotic stars. We describe the empirical approach to models and use the observational data to diagnose the physical conditions in the symbiotics stars. Finally, we compare the results of this empirical approach with existing models and discuss unresolved problems requiring new observational and theoretical work.

Friedjung, Michael↗
NASA NTRS2014

Symbiotic Stars in X-rays

Until recently, symbiotic binary systems in which a white dwarf accretes from a red giant were thought to be mainly a soft X-ray population. Here we describe the detection with the X-ray Telescope (XRT) on the Swift satellite of 9 white dwarf symbiotics that were not previously known to be X-ray sources and one that was previously detected as a supersoft X-ray source. The 9 new X-ray detections were the result of a survey of 41 symbiotic stars, and they increase the number of symbiotic stars known to be X-ray sources by approximately 30%. Swift/XRT detected all of the new X-ray sources at energies greater than 2 keV. Their X-ray spectra are consistent with thermal emission and fall naturally into three distinct groups. The first group contains those sources with a single, highly absorbed hard component, which we identify as probably coming from an accretion-disk boundary layer. The second group is composed of those sources with a single, soft X-ray spectral component, which likely arises in a region where low-velocity shocks produce X-ray emission, i.e. a colliding-wind region. The third group consists of those sources with both hard and soft X-ray spectral components. We also find that unlike in the optical, where rapid, stochastic brightness variations from the accretion disk typically are not seen, detectable UV flickering is a common property of symbiotic stars. Supporting our physical interpretation of the two X-ray spectral components, simultaneous Swift UV photometry shows that symbiotic stars with harder X-ray emission tend to have stronger UV flickering, which is usually associated with accretion through a disk. To place these new observations in the context of previous work on X-ray emission from symbiotic stars, we modified and extended the alpha/beta/gamma classification scheme for symbiotic-star X-ray spectra that was introduced by Muerset et al. based upon observations with the ROSAT satellite, to include a new sigma classification for sources with hard X-ray emission from the innermost accretion region. Since we have identified the elusive accretion component in the emission from a sample of symbiotic stars, our results have implications for the understanding of wind-fed mass transfer in wide binaries, and the accretion rate in one class of candidate progenitors of type Ia supernovae.

stars↗
NASA NTRS2005

Outbursts in Symbiotic Binaries: Z and Continued Observation

A major question for symbiotic stars concerns the nature and cause of their outbursts. A small subset of symbiotics, the "slow novae" are fairly well established as thermonuclear events that last on the order of decades. The several symbiotic "recurrent novae", which are much shorter and last on the order of months, are also thought to be thermonuclear runaways. Yet the majority of symbiotics are neither slow novae nor recurrent novae. These are the so-called "classical symbiotics," many of which show outbursts whose cause is not well understood. In some cases, jets are produced in association with an outburst, therefore an investigation into the causes of outbursts will yield important insights into the production of collimated outflows. To investigate the cause and nature of classical symbiotic outbursts, we initiated a program of multi- wavelength observations of these events. First of all in FUSE Cycle 2, we obtained six observational epochs of the 2000-2002 classic symbiotic outburst in the first target of our campaign - class prototype, Z Andromedae. That program was part of a coordinated multi-wavelength Target-of-Opportunity (TOO) campaign with FUSE, XMM, Chandra, MERLIN, the VLA, and ground-based spectroscopic and high time-resolution photometric observations. Our campaign proved the concept, utility, and need for coordinated multi-wavelength observations in order to make progress in understanding the nature of the outburst mechanisms in symbiotic stars. Indeed, the FUSE data were the cornerstone of this project. The present program is a continuation of that cycle 2 effort. Indeed, the observations acquired in this program are vital to the proper interpretation of the material acquired in cycle 2 as the new data cover the critical time period when the star continues to decline from outburst and actually returns to quiescence. The utilization of these data have allowed us to refine and complete description of our new model for classical symbiotic system outbursts.

Sonneborn, George↗
NASA NTRS1982

The symbiotics as binary stars

According to the original definition, symbiotic stars have combination spectra, in which the high-excitation emission lines regularly found in planetary nebulae are superposed on a low-temperature absorption spectrum. In connection with this investigation, the coexistence of a He II emission with the TiO absorption bands is also postulated. Attention is given to a summary of observed properties of symbiotics, binaries with a late-type giant component, possible models for the symbiotics, models with an accreting main-sequence star (Algol symbiotics), T Coronae borealis as a possible cataclysmic Algol-type symbiotic, binaries with rejuvenated degenerate dwarfs (novalike symbiotics), questions regarding the existence of PN symbiotics or subdwarfs unpowered by accretion, and related binary systems which are not symbiotics.

Plavec, M. J.↗
NASA NTRS2005

Outbursts in Symbiotic Binaries

A major question for symbiotic stars concerns the nature and cause of their outbursts. A small subset of symbiotics, the slow novae are fairly well established as thermonuclear events that last on the order of decades. The several symbiotic recurrent novae, which are much shorter and last on the order of months, are also thought to be thermonuclear runaways. Yet the majority of symbiotics are neither slow novae nor recurrent novae. These are the so-called classical symbiotics, many of which show outbursts whose cause is not well understood. In some cases, jets are produced in association with an outburst, therefore an investigation into the causes of outbursts will yield important insights into the production of collimated outflows. To investigate the cause and nature of classical symbiotic outbursts, we initiated a program of multiwavelength observations of these events. In FUSE Cycle 2, we obtained six observational epochs of the 2000-2002 classic symbiotic outburst in the first target of our campaign - class prototype, Z Andromedae. That program was part of a coordinated multi-wavelength Target-of-Opportunity (TOO) campaign with FUSE, XMM, Chandra, MERLIN, the VLA, and ground-based spectroscopic and high time-resolution photometric observations. Our campaign proved the concept, utility, and need for coordinated multi-wavelength observations in order to make progress in understanding the nature of the outburst mechanisms in symbiotic stars. Indeed, the FUSE data were the cornerstone of this project

Sonneborn, George↗
NASA NTRS2016

SU Lyncis, a Hard X-Ray Bright M Giant: Clues Point to a Large Hidden Population of Symbiotic Stars

Symbiotic star surveys have traditionally relied almost exclusively on low resolution optical spectroscopy. However, we can obtain amore reliable estimate of their total Galactic population by using all available signatures of the symbiotic phenomenon. Here we report the discovery of a hard X-ray source, 4PBC J0642.9+5528, in the Swift hard X-ray all-sky survey, and identify it with a poorly studied red giant, SU Lyn, using pointed Swift observations and ground-based optical spectroscopy. The X-ray spectrum, the optical to UV spectrum, and the rapid UV variability of SU Lyn are all consistent with our interpretation that it is a symbiotic star containing an accreting white dwarf. The symbiotic nature of SU Lyn went unnoticed until now, because it does not exhibit emission lines strong enough to be obvious in low resolution spectra. We argue that symbiotic stars without shell-burning have weak emission lines, and that the current lists of symbiotic stars are biased in favour of shell-burning systems. We conclude that the true population of symbiotic stars has been underestimated, potentially by a large factor.

binaries: symbiotic aEuro" stars: individual: SU L↗
NASA NTRS1993

Discussion on selected symbiotic stars

Because of its large variety of aspects, the symbiotic phenomenon is not very suitable for a statistical treatment. It is also not clear whether symbiotic stars really represent a homogeneous group of astrophysical objects or a collection of objects of different natures but showing similar phenomena. However we are especially interested in the symbiotic phenomenon, i.e., in those physical processes occurring in the atmosphere of each individual object and in their time dependence. Such a research can be performed through the detailed analysis of individual objects. This study should be done for a time long enough to cover all the different phases of their activity, in all the spectral ranges. Since the typical time scale of the symbiotic phenomena is up to several years and decades, this represents a problem since, for instance, making astronomy outside the visual region is a quite new field of research. It was a fortunate case that a few symbiotic stars (Z And, AG Dra, CH Cyg, AX Per, and PU Vul) had undergone remarkable light variations (or 'outbursts') in recent years, which could have been followed in the space ultraviolet with IUE, and simultaneously in the optical and IR with ground-based telescopes. But, in general, the time coverage of most of the symbiotic objects is too short to have a complete picture of their behavior. In this regard, one should recall Mayall's remark about the light curve of Z And: 'Z Andromedae is another variable that shows it will require several hundred years of observations before a good analysis can be made of its variations'. This pessimistic remark should be considered as a note of caution for those involved in the interpretation of the observations. We shall discuss a number of individual symbiotic stars for which the amount of observational data is large enough to draw a rather complete picture of their general behavior and to make consistent models. We shall especially illustrate the necessary steps toward an empirical model and take the discussion of the individual objects as a useful occasion to describe different techniques of diagnosis.

Viotti, Roberto↗
NASA NTRS1997

Physical Structure of Four Symbiotic Binaries

Disk accretion powers many astronomical objects, including pre-main sequence stars, interacting binary systems, and active galactic nuclei. Unfortunately, models developed to explain the behavior of disks and their surroundings - boundary layers, jets, and winds - lack much predictive power, because the physical mechanism driving disk evolution - the viscosity - is not understood. Observations of many types of accreting systems are needed to constrain the basic physics of disks and provide input for improved models. Symbiotic stars are an attractive laboratory for studying physical phenomena associated with disk accretion. These long period binaries (P(sub orb) approx. 2-3 yr) contain an evolved red giant star, a hot companion, and an ionized nebula. The secondary star usually is a white dwarf accreting material from the wind of its red giant companion. A good example of this type of symbiotic is BF Cygni: our analysis shows that disk accretion powers the nuclear burning shell of the hot white dwarf and also manages to eject material perpendicular to the orbital plane (Mikolajewska, Kenyon, and Mikolajewski 1989). The hot components in other symbiotic binaries appear powered by tidal overflow from a very evolved red giant companion. We recently completed a study of CI Cygni and demonstrated that the accreting secondary is a solar-type main sequence star, rather than a white dwarf (Kenyon et aL 1991). This project continued our study of symbiotic binary systems. Our general plan was to combine archival ultraviolet and optical spectrophotometry with high quality optical radial velocity observations to determine the variation of line and continuum sources as functions of orbital phase. We were very successful in generating orbital solutions and phasing UV+optical spectra for five systems: AG Dra, V443 Her, RW Hya, AG Peg, and AX Per. Summaries of our main results for these systems appear below. A second goal of our project was to consider general models for the outbursts of symbiotic stars, with an emphasis on understanding the differences between disk-driven and nuclear-powered eruptions.

Kenyon, Scott J.↗
NASA NTRS1984

Symbiotic stars

The physical characteristics of symbiotic star systems are discussed, based on a review of recent observational data. A model of a symbiotic star system is presented which illustrates how a cool red-giant star is embedded in a nebula whose atoms are ionized by the energetic radiation from its hot compact companion. UV outbursts from symbiotic systems are explained by two principal models: an accretion-disk-outburst model which describes how material expelled from the tenuous envelope of the red giant forms an inwardly-spiralling disk around the hot companion, and a thermonuclear-outburst model in which the companion is specifically a white dwarf which superheats the material expelled from the red giant to the point where thermonuclear reactions occur and radiation is emitted. It is suspected that the evolutionary course of binary systems is predetermined by the initial mass and angular momentum of the gas cloud within which binary stars are born. Since red giants and Mira variables are thought to be stars with a mass of one or two solar mass, it is believed that the original cloud from which a symbiotic system is formed can consist of no more than a few solar masses of gas.

Kafatos, M.↗
NASA NTRS1988

Multifrequency observations of symbiotic stars

The discovery of symbiotic stars is described, and the results of multifrequency observations made during the past two decades are presented. Observational data identify symbiotic stars as long-period binary systems that can be divided into two basic physical classes: detached symbiotics containing a red giant (or a Mira variable), and semidetached symbiotics containing a lobe-filling red giant and a solar-type main sequence star. Three components are typically observed: (1) the cool giant component with an effective temperature of 2500-4000 K, which can be divided by the IR spectral classification into normal M giants (S-types) and heavily reddened Mira variables (D-types); (2) the hot companion displaying a bright blue continuum at UV wavelengths, which is sometimes also an X-ray source; and (3) a gaseous nebula enveloping the binary.

Kenyon, Scott J.↗
NASA NTRS1990

A polarimetric survey of symbiotic stars

Optical and near-infrared polarization observations of 24 symbiotic stars, 14 observed with polarimetry for the first time are presented. In combination with published data, it is found that about 50 percent of the symbiotics observed polarimetrically show evidence for intrinsic polarization. The results are discussed in the light of previous observations, and comments are made on the temporal variability and wavelength dependence of the polarization. Dust scattering is identified as the dominant mechanism producing polarization in symbiotic stars. While it cannot be excluded that some symbiotic systems are completely engulfed in their dust shells, the data indicate that the H-alpha emission line may originate from outside of the dust-scattering envelopes in some systems.

Schulte-Ladbeck, R. E.↗
NASA NTRS1993

Overview of the observations of symbiotic stars

The term Symbiotic stars commonly denotes variable stars whose optical spectra simultaneously present a cool absorption spectrum (typically TiO absorption bands) and emission lines of high ionization energy. This term is now used for the category of variable stars with composite spectrum. The main spectral features of these objects are: (1) the presence of the red continuum typical of a cool star, (2) the rich emission line spectrum, and (3) the UV excess, frequently with the Balmer continuum in emission. In addition to the peculiar spectrum, the very irregular photometric and spectroscopic variability is the major feature of the symbiotic stars. Moreover, the light curve is basic to identify the different phases of activity in a symbiotic star. The physical mechanisms that cause the symbiotic phenomenon and its variety are the focus of this paper. An astronomical phenomenon characterized by a composite stellar spectrum with two apparently conflicting features, and large variability has been observed. Our research set out to find the origin of this behavior and, in particular, to identify and measure the physical mechanism(s) responsible for the observed phenomena.

Viotti, Roberto↗
NASA NTRS2004

Outbursts in Symbiotic Binaries

Two models have been proposed for the outbursts of symbiotic stars. In the thermonuclear model, outbursts begin when the hydrogen burning shell of a hot white dwarf reaches a critical mass. After a rapid increase in the luminosity and effective temperature, the white dwarf evolves at constant luminosity to lower effective temperatures, remains at optical maximum for several years, and then returns to quiescence along a white dwarf cooling curve. In disk instability models, the brightness rises when the accretion rate from the disk onto the central white dwarf abruptly increases by factors of 5-20. After a few month to several year period at maximum, both the luminosity and the effective temperature of the disk decline as the system returns to quiescence. If most symbiotic stars undergo thermonuclear eruptions, then symbiotics are probably poor candidates for type I supernovae. However, they can then provide approx. 10% of the material which stars recycle back into the interstellar medium. If disk instabilities are the dominant eruption mechanism, symbiotics are promising type Ia candidates but recycle less material into the interstellar medium.

Sonneborn, George↗
NASA NTRS1981

Ingress observations of the 1980 eclipse of the symbiotic star CI Cyngni

One of the major results from the IUE may prove to be the knowledge gained by studies of the ultraviolet spectra of symbiotic stars. Symbiotics combine spectral features of a cool M giant like photosphere with strong high excitation emission lines of nebular origin, superposed. The UV spectra are dominated by intense permitted and semiforbidden emission lines and weak continua indicative of hot compact objects and accretion disks. Two symbiotics, AR Pav and CI Cyg are thought to be eclipsing binaries and IUE observations during the 1980 eclipse of CI Cygni are discussed.

Stencel, R. E.↗
NASA NTRS1982

Ultraviolet properties of the symbiotic stars

A general discussion of the UV spectra of symbiotic stars, including both the emission lines and the continua, is presented, with AG Pegasi considered as an illustrative example. It is noted that the IUE observations of the symbiotics have revealed UV properties which rival the diversity of the optical features. Nevertheless, the UV data have for the first time permitted the hot component to be studied relatively uncontaminated by the giant companion, which dominates the optical regime. The UV observations provide convincing evidence that many of the symbiotics have hot stellar companions embedded in the enshrouding nebula or accretion shell formed from the wind from one or possibly both of the components.

Slovak, M. H.↗
NASA NTRS1984

ZZ Canis Minoris as a symbiotic star

The H-aplha and Na I D-line regions of the M6 giant star ZZ Canis Minoris (ZZ CMi) were observed with the Kitt Peak coude feed telescope and a CCD detector. It is shown that ZZ CMi has similar spectroscopic and photoproperties to the symbiotic star EG And. The data are used to argue for the classification of ZZ CMi as a symbiotic star despite its current listing in the General Catalog of Variable Stars (GCVS) as a semi-regular variable. The infrared magnitudes of ZZ CMi and the known symbiotic stars are compared in a table.

Bopp, B. W.↗
NASA NTRS1987

The (C III lambda 1909/Si III lambda 1892) ratio as a diagnostic for planetary nebulae and symbiotic stars

Suitable IUE archival material on planetary nebulae has been examined to determine the log R /F(lambda 1909 C III)/F(lambda 1892 Si III)/ as a discriminant for distinguishing planetary nebulae from symbiotic stars and related objects. The mean value of log R for 73 galactic planetaries is 1.4, while that of extragalactic planetaries appears to be slightly lower, and that for symbiotics is 0.3. The lower value of log R for symbiotics is easily understood as a consequence of their higher densities. A plot of log R versus N-epsilon indicates that 80 percent of the planetaries fall into the range of log R between 1.2 and 1.8, but some of the 'peculiar' and bipolar nebulae fall below log R = 1.2. The corresponding N(C++)/N(Si++) ionic ratio varies over a large range.

Feibelman, Walter A.↗