1,902 research outputs found
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 the common characteristics to all the systems: 1) at
least two dust shells are clearly present, one at \sim 1000 K and the other at
\sim 400 K; they dominate the emission in the IR; 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 WD 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 are
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 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 K and <=400 K, while, in the
case of late giants, they spread more uniformly throughout the same range.Comment: 14 pages, 7 figures, 5 tables. Accepted for publication in MNRA
The symbiotic star H1-36. A composite model of line and continuum spectra from radio to ultraviolet
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 taking
into account the observational data along the whole electromagnetic spectrum,
in order to derive a self-consistent picture able to interpret the nature of
the system as a whole. 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 taking into account all the
emitting contributions arising from both the stars, the dust shells and the
gaseous nebulae. A comprehensive model of the radio spectra allows to reproduce
the different slopes of the radio profile and the turnover frequency, as well
as the different size of the observed shocked envelope at different frequencies
in the light of the different contributions from the expanding and reverse
nebulae. 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. This insight
leads us to indicate H1-36 as a promising X-ray target and to encourage
observations and studies which consistently take into account the complex
nature of symbiotic stars throughout the whole electromagnetic spectrum.Comment: 8 pages, 3 figures, 5 tables, accepted for publication in A&A on 2th
May 200
Shock fronts in the symbiotic system BI Crucis
We investigate the symbiotic star BI Crucis through a comprehensive and
self-consistent analysis of the spectra emitted in three different epochs:
60's, 70's, and late 80's. In particular, we would like to find out the
physical conditions in the shocked nebula and in the dust shells, as well as
their location within the symbiotic system, by exploiting both photometric and
spectroscopic data from radio to UV. We suggest a model which, on the basis of
optical imaging, emission line ratios and spectral energy distribution profile,
is able to account for collision of the winds, formation of lobes and jets by
accretion onto the WD, as well as for the interaction of the blast wave from a
past, unrecorded outburst with the ISM. We have found that the spectra observed
throughout the years show the marks of the different processes at work within
BI Cru, perhaps signatures of a post-outburst evolution. We then call for new
infrared and millimeter observations, potentially able to resolve the inner
structure of the symbiotic nebula.Comment: 13 pages, 9 figures, 2 tables; accepted for publication in MNRA
The symbiotic star CH Cygni. II. The broad Ly alpha emission line explained by shocks
Context. In 1985, at the end of the active phase 1977-1986, a broad (4000
km/s) Ly alpha line appeared in the symbiotic system CH Cygni that had never
been observed previously. Aims. In this work we investigate the origin of this
anomalous broad Ly alpha line. Methods. We suggest a new interpretation of the
broad Ly alpha based on the theory of charge transfer reactions between ambient
hydrogen atoms and post-shock protons at a strong shock front. Results. We have
found that the broad Ly alpha line originated from the blast wave created by
the outburst, while the contemporary optical and UV lines arose from the nebula
downstream of the expanding shock in the colliding wind scenario.Comment: 5 pages, 2 figures, accepted for publication in A&A on 7th April 200
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