16 research outputs found
The applicability of the wind compression model
Compression of the stellar winds from rapidly rotating hot stars is described
by the wind compression model. However, it was also shown that rapid rotation
leads to rotational distortion of the stellar surface, resulting in the
appearance of non-radial forces acting against the wind compression. In this
note we justify the wind compression model for moderately rotating white dwarfs
and slowly rotating giants. The former could be conducive to understanding
density/ionization structure of the mass outflow from symbiotic stars and
novae, while the latter can represent an effective mass-transfer mode in the
wide interacting binaries.Comment: 3 pages, A&
Early evolution of the extraordinary Nova Del 2013 (V339 Del)
We determine the temporal evolution of the luminosity L(WD), radius R(WD) and
effective temperature Teff of the white dwarf (WD) pseudophotosphere of V339
Del from its discovery to around day 40. Another main objective was studying
the ionization structure of the ejecta. These aims were achieved by modelling
the optical/near-IR spectral energy distribution (SED) using low-resolution
spectroscopy (3500 - 9200 A), UBVRcIc and JHKLM photometry. During the fireball
stage (Aug. 14.8 - 19.9, 2013), Teff was in the range of 6000 - 12000 K, R(WD)
was expanding non-uniformly in time from around 66 to around 300 (d/3 kpc)
R(Sun), and L(WD) was super-Eddington, but not constant. After the fireball
stage, a large emission measure of 1.0-2.0E+62 (d/3 kpc)**2 cm**(-3)
constrained the lower limit of L(WD) to be well above the super-Eddington
value. The evolution of the H-alpha line and mainly the transient emergence of
the Raman-scattered O VI 1032 A line suggested a biconical ionization structure
of the ejecta with a disk-like H I region persisting around the WD until its
total ionization, around day 40. It is evident that the nova was not evolving
according to the current theoretical prediction. The unusual non-spherically
symmetric ejecta of nova V339 Del and its extreme physical conditions and
evolution during and after the fireball stage represent interesting new
challenges for the theoretical modelling of the nova phenomenon.Comment: 14 pages, 9 figures, 3 tables, accepted for Astronomy and
Astrophysic
Formation of a disk structure in the symbiotic binary AX Per during its 2007-10 precursor-type activity
AX Per is an eclipsing symbiotic binary. During active phases, deep narrow
minima are observed in its light curve, and the ionization structure in the
binary changes significantly. From 2007.5, AX Per entered a new active phase.
It was connected with a significant enhancement of the hot star wind.
Simultaneously, we identified a variable optically thick warm (Teff ~ 6000 K)
source that contributes markedly to the composite spectrum. The source was
located at the hot star's equator and has the form of a flared disk, whose
outer rim simulates the warm photosphere. The formation of the neutral
disk-like zone around the accretor during the active phase was connected with
its enhanced wind. We suggested that this connection represents a common origin
of the warm pseudophotospheres that are indicated during the active phases of
symbiotic stars.Comment: 13 pages, 9 figures, 8 tables, accepted for A&
Formation of Neutral Disk-Like Zone Around the Active Hot Stars in Symbiotic Binaries
In this contribution we present the ionization structure in the enhanced wind from the hot star in symbiotic binaries during active phases. Rotation of the hot star leads to the compression of the outflowing material towards its equatorial plane. As a result, a neutral disk-like zone around the active hot star near the orbital plane is created. We modeled the compression of the wind and calculated the neutral disk-like zone in the enhanced wind from the hot star using the equation of the photoionization equilibrium. the presence of such neutral disk-like zones was also suggested on the basis of the modeling the spectral energy distribution of symbiotic binaries. We confront the calculated ionization structures in the enhanced wind from the hot star with the observations. the calculated column density of the neutral hydrogen atoms in the neutral disk-like zone and the emission measure of the ionized part of the wind from the hot star are in a good agreement with the quantities derived from observations during active phases. the presence of such neutral disk-like zones is transient, being connected with the active phases of symbiotic binaries. During quiescent phases, such neutral disk-like zones cannot be created because of insufficient mass-loss rate from the hot star
Wind mass transfer in S-type symbiotic binaries
Context. Luminosities of hot components in symbiotic binaries require accretion rates that are higher than those that can be achieved via a standard Bondi-Hoyle accretion. This implies that the wind mass transfer in symbiotic binaries has to be more efficient.
Aims. We suggest that the accretion rate onto the white dwarfs (WDs) in S-type symbiotic binaries can be enhanced sufficiently by focusing the wind from their slowly rotating normal giants towards the binary orbital plane.
Methods. We applied the wind compression model to the stellar wind of slowly rotating red giants in S-type symbiotic binaries.
Results. Our analysis reveals that for typical terminal velocities of the giant wind, 20 to 50 km s-1, and measured rotational velocities between 6 and 10 km s-1, the densities of the compressed wind at a typical distance of the accretor from its donor correspond to the mass-loss rate, which can be a factor of ~10 higher than for the spherically symmetric wind. This allows the WD to accrete at rates of 10-8−10-7 M⊙ yr-1, and thus to power its luminosity.
Conclusions. We show that the high wind-mass-transfer efficiency in S-type symbiotic stars can be caused by compression of the wind from their slowly rotating normal giants, whereas in D-type symbiotic stars, the high mass transfer ratio can be achieved via the gravitational focusing, which has recently been suggested for very slow winds in Mira-type binaries