Shock fronts in the symbiotic system BI Crucis (original) (raw)
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The spectral energy distribution of D-type symbiotic stars: the role of dust shells
We have collected continuum data of a sample of D-type symbiotic stars. By modelling their spectral energy distribution in a colliding-wind theoretical scenario we have found characteristics common to all the systems: (1) at least two dust shells are clearly present, one at ~1000K and the other at ~400K they dominate the emission in the infrared; (2) the radio data are explained by thermal self-absorbed emission from the reverse shock between the stars; while (3) the data in the long wavelength tail come from the expanding shock outwards the system; (4) in some symbiotic stars, the contribution from the white dwarf in the UV is directly seen. Finally, (5) for some objects soft X-ray emitted by bremsstrahlung downstream of the reverse shock between the stars is predicted. The results thus confirm the validity of the colliding-wind model and the important role of the shocks. The comparison of the fluxes calculated at the nebula with those observed at the Earth reveals the distribution throughout the system of the different components, in particular the nebulae and the dust shells. The correlation of shell radii with the orbital period shows that larger radii are found at larger periods. Moreover, the temperatures of the dust shells regarding the sample are found at ~1000 and <=400K, while in the case of late giants they spread more uniformly throughout the same range.
The X-ray Evolution of the Symbiotic Star V407 Cygni during its 2010 Outburst
2012
We present a summary of Swift and Suzaku X-ray observations of the 2010 nova outburst of the symbiotic star, V407 Cyg. The Suzaku spectrum obtained on day 30 indicates the presence of the supersoft component from the white dwarf surface, as well as optically thin component from the shock between the nova ejecta and the Mira wind. The Swift observations then allow us to track the evolution of both components from day 4 to day 150. Most notable is the sudden brightening of the optically thin component around day 20. We identify this as the time when the blast wave reached the immediate vicinity of the photosphere of the Mira. We have developed a simple model of the blast wave-wind interaction that can reproduce the gross features of the X-ray evolution of V407 Cyg, and explore a parameter space of ejected mass, binary separation and Mira mass loss rate.. If the model is correct, the binary separation is likely to be larger then previously suggested and the mass loss rate of the Mira is likely to be relatively low.
Gas and dust spectra of the D' type symbiotic star HD 330036
Aims:We present a comprehensive and self-consistent modelling of the D' type symbiotic star (SS) HD 330036 from radio to UV. Methods: Within a colliding-wind scenario, we analyse the continuum, line, and dust spectra by means of SUMA, a code that simulates the physical conditions of an emitting gaseous cloud under the coupled effect of ionisation from an external radiation source and shocks. Results: We find that the UV lines are emitted from high-density gas between thestars downstream of the reverse shock, while the optical lines are emitted downstream of the shock propagating outwards from the system. As regards the continuum SED, three shells are identified in the IR, at 850 K, 320 K, and 200 K with radii r = 2.8 × 1013 cm, 4 × 1014 cm, and 1015 cm, respectively, after adopting a distance to Earth of d=2.3 kpc. Interestingly, all these shells appear to be circumbinary. Analysis of the unexploited ISO-SWS spectrum reveals that both PAHs and crystalline silicates coexist in HD 330036, with PAHs associated to the internal shell at 850 K, and crystalline silicates stored in the cool shells at 320 K and 200 K. Strong evidence that crystalline silicates are shaped in a disk-like structure is derived on the basis of the relative band strengths. Finally, we suggest that shocks can be a reliable mechanism for activating the annealing and the consequent crystallisation processes. Conclusions: We show that a consistent interpretation of gas and dust spectra emitted by SS can be obtained by models that account for the coupled effect of the photoionising flux and of shocks. The VLTI/MIDI proposal recently accepted by ESO aims to verify and better constrain some of our results by means of IR interferometric observations.
Gas and Dust Spectral Analysis of Galactic and Extragalactic Symbiotic Stars
PhD Thesis, School of Astrophysics, University of Padova (Italy), 2009
Symbiotic stars are recognized as unique laboratories for studying a large variety of phenomena that are relevant to a number of important astro-physical problems. This PhD thesis deals with a spectral analysis of galactic and extragalactic symbiotic stars. The former are mainly D-type symbiotic stars for which a comprehensive study, from radio to X-ray spectral region, has been performed. With the latter, we refer to symbiotic stars in the Magellanic Clouds, to be analyzed mainly in the IR range. The common theoretical scenario that lies in the background of this work is the colliding-wind model, developed already during the 80's, supported by first observational evidence at the beginning of 90's (mainly thanks to Nussbaumer and collaborators), and finally completed with detailed and powerful hydrodynamical simulations by various authors in these recent years. In the light of this scenario, we have tried to interpret gas and dust spectra of our targets in a unique and self-consistent way. The spectral analysis has been performed by means of the numerical code SUMA, developed at the Instituto Astronomico e Geofisico of the University of Sao Paulo by Sueli M. Viegas (Aldrovandi) and Marcella Contini from the School of Physics and Astronomy of the Tel-Aviv University.
Asymmetric Planetary Nebulae III ASP Conference Series, Vol. XXX, 2004
2003
Recent observations of the Egg Nebula (AFGL 2688), obtained at ever-increasing spatial and spectral resolution, have revealed a perplexing array of phenomena. Many of these phenomena present challenges to our understanding of this object as an emerging, bipolar planetary nebula. Here, we consider two particularly intriguing aspects of the Egg: the peculiar structure and kinematics of its equatorial regions, and the nature of an apparent widely separated companion to the central star. In the first case, we use recently acquired Hubble Space Telescope images to demonstrate that the H2 emission distributed east and west of the central star is spatially coincident with a dusty, equatorial disk or torus. The H2 is thus constrained to lie near the equatorial plane, casting doubt on pure radial outflow models for the equatorial kinematics. In the second case, we show that the apparent companion (“Peak A”) may be an accreting white dwarf that has undergone one or more thermonuclear bursts. ...
The symbiotic star H1-36. A composite model of line and continuum spectra from radio to ultraviolet
Aims:In this paper, we analyse the spectra of D-type SS H1-36 within a colliding-wind scenario. We aim to analyse the properties of this object by taking the observational data along the whole electromagnetic spectrum into account, in order to derive a self-consistent picture able to interpret the nature of the system as a whole. Methods: After constraining the relative physical conditions by modelling more than 40 emission lines from radio to UV, we are able to explain the continuum spectral energy distribution by considering all the emitting contributions arising from both the stars, the dust shells, and the gaseous nebulæ. Results: A comprehensive model of the radio spectra allows reproduction of the different slopes of the radio profile and the turnover frequency, as well as the different sizes of the observed shocked envelope at different frequencies in the light of the contributions from the expanding and reverse nebulæ. The IR continuum unveils the presence of two dust shells with different radii and temperatures, which might be a distinctive feature of D-type symbiotic systems as a class of objects. The broad profiles of IR lines direct us to investigate whether an X-ray jet may be present. Conclusions: This insight leads us to indicate H1-36 as a promising X-ray target and to encourage observations and studies that consistently take the complex nature of symbiotic stars into account throughout the whole electromagnetic spectrum.
A narrowband imaging survey of symbiotic stars
Astronomy and …, 1999
Narrowband images of 51 symbiotic stars were obtained at the ESO and ORM observatories to search for resolved optical nebulae. Ionized nebulae much larger than previously known are found around CH Cyg, HM Sge and V1016 Cyg, and they will be discussed in detail in forthcoming papers. A nebula with a deconvolved size between 0. 9 and 1. 5 is found around the symbiotic Mira H 1-36. The radio sources located few arcminutes aside of R Aqr (Hollis et al. 1987), which were suggested to be the remnant of a prehistoric eruption of the system, are found to be background galaxies. We also present a bibliographical compilation, updated to October 1998, of all the extended nebulae around symbiotic stars detected at optical and radio wavelengths, as well as a list of optical non-detections. The statistics of occurrence of these large ionized nebulae among symbiotic stars is discussed. Extended ionized nebulae appear to be a common component of the D-type symbiotics, and we infer that they are formed by the Mira wind and/or high velocity winds ejected by the hot component during outbursts. On the contrary, very few nebulae are detected around the systems containing normal red giants 1 .
The shock structure in the protoplanetary nebula M1-92: imaging of atomic and H_2 line emission
1998
We present HST imaging of continuum (5500Å) and atomic line (Hα, [OI] 6300Å, [SII] 6717 and 6731Å, and [OIII] 5007Å) emissions in the protoplanetary nebula M 1-92. Ground based imaging of 2µm continuum and H 2 ro-vibrational (S(1) v=1-0 and v=2-1 lines) emission has been also performed. The 5500Å continuum is due to scattering of the stellar light by grains in a double-lobed structure comparable in extent and total density with the molecular envelope detected at mm wavelengths, which consists of two empty shells with a clear axis of symmetry. On the other hand, the optical line emission comes mainly from two chains of shocked knots placed along the symmetry axis of the nebula and inside those cavities, for which relatively high excitation is deduced (shock velocities of about 200 km s −1 ). The H 2 emission probably comes from more extended regions with representative temperature and density of 1600 K and 6 10 3 cm −3 , intermediate in location and excitation between the atomic line knots and the very cold region detected in CO emission. We argue that the chains of knots emitting in atomic lines correspond to shocks taking place in the post-AGB bipolar flow. The models for interstellar Herbig-Haro objects seem to agree with the observations, at least qualitatively, explaining in particular that the atomic emission from the bipolar flow dominates over that from shocks propagating in the AGB shell. Models developed for protoplanetary nebula dynamics fail, however, to explain the strong concentration of the atomic emission along the symmetry axis.
A photo-ionised canopy for the shock-excited Criss-Cross nebula
Astronomy and Astrophysics, 2007
Aims. We study a new broad well-defined arc of optical nebulosity close to the cloud-shock interacting Criss-Cross Nebula, derive the basic physical properties of the former and revise those of the latter, and compare both objects to simulations of cloud-shock interactions from the literature. Methods. Deep optical, partly wide-field, images were used to reveal the intricate morphology and overall extent of the nebulosities. Optical spectroscopy enabled us to uncover their nature. Results. The two nebulosities obviously are physically linked, but are of different type; the Criss-Cross Nebula is, as was shown also in an earlier paper, excited via a slow shock from the expanding Orion-Eridanus Bubble, but the broad arc is definitely photoionized. The source for ionizing photons appears to be hot gas in this bubble. Some results of simulations of interactions of SNRs with interstellar clouds available from the literature bear a striking resemblance to our nebulae, which appear to represent an example -unrivalled in closeness and clarity -for an early to medium stage in the destruction of an isolated cloud over-run by a highly evolved SNR. Thereby the Criss-Cross Nebula is, when seen from the SNR, the rear disrupted part of the original small cloud, whereas the arc probably is its yet rather intact front part.
Eprint Arxiv Astro Ph 0701404, 2007
Aims. We investigate the dynamics of the nebula around the symbiotic star Hen 2-147, determine its expansion parallax, and compare it with the distance obtained via the period-luminosity relation for its Mira variable. Methods. A combination of multi-epoch HST images and VLT integral field high-resolution spectroscopy is used to study the nebular dynamics both along the line of sight and in the plane of the sky. These observations allow us to build a 3D spatio-kinematical model of the nebula, which, together with the measurement of its apparent expansion in the plane of the sky over a period of 3 years, provides the expansion parallax for the nebula. Additionally, SAAO near-infrared photometry obtained over 25 years is used to determine the Mira pulsation period and derive an independent distance estimation via the period-luminosity relationship for Mira variables.