47 research outputs found
Wind mass transfer in S-type symbiotic binaries III. Confirmation of a wind focusing in EG Andromedae from the nebular [OIII]\lambda 5007 line
Context. The structure of the wind from the cool giants in symbiotic binaries
carries important information for understanding the wind mass transfer to their
white dwarf companions and its fuelling. Aims. In this paper, we indicate a
non-spherical distribution of the neutral wind zone around the red giant (RG)
in the symbiotic binary star, EG And. Methods. We achieved this aim by
analysing the periodic orbital variations of fluxes and radial velocities of
individual components of the H and [OIII]5007 lines observed
on our high-cadence medium (R 11 000) and high-resolution (R 38
000) spectra. Results. The asymmetric shaping of the neutral wind zone at the
near-orbital-plane region is indicated by: (i) the asymmetric course of the
H core emission fluxes along the orbit; (ii) the presence of their
secondary maximum around the orbital phase , which is possibly
caused by the refraction effect; and (iii) the properties of the H
broad wing emission originating by Raman scattering on H atoms. The wind is
substantially compressed from polar directions to the orbital plane as
constrained by the location of the [OIII]5007 line emission zones in
the vicinity of the RG at/around its poles. The corresponding mass-loss rate
from the polar regions of Msun/yr is a factor of lower than the average rate of Msun/yr derived from
nebular emission of the ionised wind from the RG. Furthermore, it is two orders
of magnitude lower than that measured in the near-orbital-plane region from
Rayleigh scattering. Conclusions. The startling properties of the nebular
[OIII]5007 line in EG And provides an independent indication of the
wind focusing towards the orbital plane.Comment: 10 pages, 8 figure
Density asymmetry and wind velocities in the orbital plane of the symbiotic binary EG Andromedae
Context. Non-dusty late-type giants without a corona and large-scale
pulsations represent objects that do not fulfil the conditions under which
standard mass-loss mechanisms can be applied efficiently. The driving mechanism
of their winds is still unknown.
Aims. The main goal of this work is to match the radial velocities of
absorbing matter with a depth in the red giant (RG) atmosphere in the S-type
symbiotic star EG And.
Methods. We measured fluxes and radial velocities of ten FeI absorption lines
from spectroscopic observations with a resolution of ~30 000. At selected
orbital phases, we modelled their broadened profiles, including all significant
broadening mechanisms.
Results. The selected FeI absorption lines at 5151 - 6469A, originate at a
radial distance ~1.03 RG radii from its centre. The corresponding radial
velocity is typically ~1 km/s , which represents a few percent of the terminal
velocity of the RG wind. The high scatter of the radial velocities of several
km/s in the narrow layer of the stellar atmosphere points to the complex nature
of the near-surface wind mass flow. The average rotational velocity of 11 km/s
implies that the rotation of the donor star can contribute to observed focusing
the wind towards the orbital plane. The orbital variability of the absorbed
flux indicates the highest column densities of the wind in the area between the
binary components, even though the absorbing neutral material is geometrically
more extended from the opposite side of the giant. This wind density asymmetry
in the orbital plane region can be ascribed to gravitational focusing by the
white dwarf companion.
Conclusions. Our results suggest that both gravitational and rotational
focusing contribute to the observed enhancement of the RG wind towards the
orbital plane, which makes mass transfer by the stellar wind highly efficient.Comment: 12 pages, 10 figure
The secondary minimum in YY Her: Evidence for a tidally distorted giant
We present and analyze quiescent UBVRI light curves of the classical
symbiotic binary YY Her. We show that the secondary minimum, which is clearly
visible only in the quiescent VRI light curves, is due to ellipsoidal
variability of the red giant component. Our simple light curve analysis, by
fitting of the Fourier cosine series, resulted in a self-consistent
phenomenological model of YY Her, in which the periodic changes can be
described by a combination of the ellipsoidal changes and a sinusoidal changes
of the nebular continuum and line emission.Comment: 5 pages, 2 figures, to appear in Astronomy & Astrophysic