colliding winds in classical symbiotic...
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COLLIDING WINDS COLLIDING WINDS IN CLASSICAL SYMBIOTIC STARSIN CLASSICAL SYMBIOTIC STARS
E. Kilpio, D. Bisikalo
Institute of Astronomy, RAS, Moscow, Russia
El Escorial, 2007
Symbiotic
stars
are
characterized
by
peculiar
spectra where
the
characteristic
features
of
a
cool
giant
are
present
together
with
emission
lines
corresponding
to
a high
excitation
level. The
red
and
infrared
spectra
of
symbiotic
stars
are
typical
of
cool
giants
while
in
the
UV range
they
are
characterized
by
a very
hot
continuum.
Symbiotic star is a wide binary consisting of a cool giant and a white dwarf surrounded by a nebulosity. It
is
a
detached
binary
with
mass
exchange
via
stellar
wind.
Symbiotic stars present nova-like outbursts. In classical symbiotic systems outbursts typically
last
a few
months
and
have
amplitudes
of
2-4m. The mechanism of outbursts in classical symbiotic systems and processes taking place during an outburst development are still poorly known.
UV range can give us a lot of information about symbiotic systems.
WDNebulosity
Accretion diskWind of a giant Hot areas formed as the result of winds collision
A. Skopal
et
al., Astron. Astrophys., 453, 279
(2006)
Most part of existing UV space missions observed symbiotic stars.
?
A typical classical symbiotic star is a detached
system with mass exchange driven by stellar wind.
EQUATIONSEQUATIONS
0u v wt x y zρ ρ ρ ρ∂ ∂ ∂ ∂+ + + =
∂ ∂ ∂ ∂
( )2
2u Pu uv uw v
t x y z xρρ ρ ρ ρ ρ
∂ +∂ ∂ ∂ ∂Φ+ + + = − + Ω
∂ ∂ ∂ ∂ ∂
( )2
2v Pv uv vw u
t x y z yρρ ρ ρ ρ ρ
∂ +∂ ∂ ∂ ∂Φ+ + + = − − Ω
∂ ∂ ∂ ∂ ∂
( )2w Pw uw vwt x y z z
ρρ ρ ρ ρ∂ +∂ ∂ ∂ ∂Φ
+ + + = −∂ ∂ ∂ ∂ ∂
E uh vh wh u v wt x y z x y zρ ρ ρ ρ ρ ρ ρ∂ ∂ ∂ ∂ ∂Φ ∂Φ ∂Φ
+ + + = − − −∂ ∂ ∂ ∂ ∂ ∂ ∂
( )1P γ ρε= −
The Roe-Osher
scheme has been used for 2D
and
SFS (simplified flux splitting) scheme for 3D.
GRIDS2D:601×601cells
689×589 cells (condensed near the accretor)3D:
253×253×85 cells
( ) ( ) ( )
22 21 1 2 2
1 2 1 2 1 22 2 2 2 2 2 2 2 21 2
12( )
GM GM GM Mx a yM Mx y z x y z x a y z
⎛ ⎞⎛ ⎞⎜ ⎟Φ = − +Γ − − Ω − +⎜ ⎟⎜ ⎟+⎝ ⎠+ + + + − + + ⎝ ⎠
M1
–
mass of the donor, r
–
distance from the center of the donor,
Г
–
parameter.
The modified potential
:
rrF 2
1
rGM
Γ=
MODELING OF A GIANTMODELING OF A GIANT’’S WINDS WIND
Z AND PARAMETERSZ AND PARAMETERS
T.Fernandez-Castro, A.Cassatella, A.Gimenez
et
al., Astrophys. J., 324, 1016 (1988)
Mass of the giant
M1 2MRadius of the giant
R1 77 R
Mass of the accretor
M2 0.6MRadius of the accretor
R2 0.07 R
Orbital period
Porb 758.8 daysSeparation A 482.53 RMass loss rate 2×10-7
M
Donor’s wind velocity 25 km/s
MECHANISM OF TRANSITION FROM MECHANISM OF TRANSITION FROM QUIESCENT TO ACTIVE STATE IN QUIESCENT TO ACTIVE STATE IN CLASSICAL SYMBIOTIC STARSCLASSICAL SYMBIOTIC STARS
NATURE OF OUTBURSTS IN SYMBIOTIC STARSNATURE OF OUTBURSTS IN SYMBIOTIC STARS
The most probable mechanism describing the observational manifestations of symbiotics
is thermonuclear burning on the
accretor's
surface (Kenyon
1986, Iben&Tutukov
1996).
The process of thermonuclear burning of hydrogen on the white dwarf surface strongly depends on the accretion rate
(Paczynski&Rudak,
1980).
The
steady
hydrogen
burning
is possible
only in a narrow range of accretion rate values
(Paczynski&Zytkow,
1978). This range depends
on the white dwarf mass.
S.J.Kenyon, The
Symbiotic
Stars, Cambridge
Univ. Press, (1986)I.Iben, A.V.Tutukov, Astrophys. J. Suppl. Ser. 105, 145 (1996)B.Paczynski
and
B.Rudak, Astron. and
Astrophys., 82, 349 (1980)B.Paczynski
and
A.Zytkow, Astrophys. J. 222, 604 (1978)
LEAVING THE STEADY BURNING RANGELEAVING THE STEADY BURNING RANGECaseCase
1.1.
Accretion rate becomes lower than the steady
burning range:
Corresponds to the observational manifestations of symbiotic novae
CaseCase
2.2.
Accretion rate exceeds the steady burning range
Timescale and brightness changes correspond to classical symbiotic stars
Accreted material becomes
exhaustedBurning
termination
Matter accumulation on the surface
Hydrogen shell
flash
Accreted matter accumulates above the
burning
shell
Expansion
to giant’s
dimensions
What is the reason of the accretion rate growthWhat is the reason of the accretion rate growth??
In order to explain the accretion rate change several mechanisms were proposed:
Significant change of the donor’s mass loss(Nussbaumer&Vogel, 1987) – not confirmed by observations
Accretion disk instabilities (Bath, 1977) – no correspondence on scale and time
REASON OF THE ACCRETION RATE REASON OF THE ACCRETION RATE GROWTHGROWTH
Using the results of gasdynamic modeling we proposed the mechanism that can provide the accretion rate growth (Bisikalo et al., 2002)
WW>1>1
–
wind accretion WW<1<1
–
disk accretion
The accretion regime is defined by the parameter
W=W=vvwindwind
/v/vorborb
DEPENDENCE OF THE FLOW STRUCTURE ON THE DEPENDENCE OF THE FLOW STRUCTURE ON THE WIND VELOCITYWIND VELOCITY
In classical symbiotics
the value of giant’s wind velocity is close to the orbital velocity so both regimes are possible.
MECHANISM PROVIDING THE ACCRETION MECHANISM PROVIDING THE ACCRETION RATE GROWTHRATE GROWTH
Minor Minor variations of variations of giantgiant’’s wind s wind
velocityvelocity
Accretion Accretion regime regime changechange
Jump of the Jump of the accretion accretion
raterate
Even
minor
variations
in
the
donor's
wind
velocity
can lead
to
the
accretion
regime
change
-
from
disk
accretion
to
wind
accretion. During
the
transition
period, namely during
the
disk
destruction
the
accretion
rate
increases
abruptly
and
exceeds
the
upper
limit
of
the
steady
burning range.
The
velocity
of
the
mass-losing
star's
wind
in
Z
And
is v=25
km/s. (Fernandez-Castro et al., 1988)
In order to check the applicability of the proposed mechanism, numerical simulations for velocities of 25±5
km/s have been carried out.
T.Fernandez-Castro, A.Cassatella, A.Gimenez
et
al., Astrophys. J., 324, 1016 (1988)
DONOR WIND VELOCITYDONOR WIND VELOCITY
V=V=20 20 KM/SKM/S
Rdisk
≈50-60R
►Accretion efficiency 22.5 -25%
►Accretion rate
►For the case of Z And
(MWD
=0.6M ), steady burning range is:
Accretion rate in the solution with the disk is within the Accretion rate in the solution with the disk is within the steady burning rangesteady burning range..
годMMaccr /105.4 8−×≈
годMMгодM accr /107.4/101.2 88 −− ×≤≤×
DONOR WIND VELOCITYDONOR WIND VELOCITY
V=V=30 30 KM/SKM/S
Accretion efficiency
11 13%accrM = −
WIND VELOCITY CHANGE 20WIND VELOCITY CHANGE 20→→30 30 KM/SKM/S
It takes about 133d
for the matter moving with increased velocity to reach the the
bow shock located in front of the
accretor.
After that the wind moves further, crushes disk and makes the matter it contained to fall onto the surface of the accretor.
This results in the accretion rate jump.
ACCRETION RATE CHANGEACCRETION RATE CHANGE
This is enough (amplitude and time that the accretion rate spends above the steady burning range) to lead to the outburst.
The
maximum value
of
the
accretion
rate
is
~ 2-2.2 times
as
compared
to
the state
with
disk
accretion.
Acc
retio
n ra
te
Time
OUTBURST DEVELOPMENT IN THE OUTBURST DEVELOPMENT IN THE FRAMEWORK OF THE COLLIDING WINDS MODELFRAMEWORK OF THE COLLIDING WINDS MODEL
There are a lot of symbiotics
where the wind from the hot component has been observed at active stages of the system (e.g. Z And). In such a case winds from both components collide and form the complex structure with shocks.
We took the stationary solution corresponding to the pre- outburst state and continued calculations with changed
boundary conditions on the accretor’s
surface.
After 70d
the waves reach their final position between the system’s components and it takes 20-30 days for the formation of shocks structure to be completed.
SHOCKS CONTRIBUTION TO THE BRIGHTNESS SHOCKS CONTRIBUTION TO THE BRIGHTNESS OF THE SYSTEMOF THE SYSTEM
Shocks formation can provide the brightness growth up to 1m
so it should be seen on the lightcurve.
Hot wind appears
(15.09.2000)
Shocks form
(~25d)
Good correspondence between the model and observations!Good correspondence between the model and observations!
U
B
V
~60d
Sokoloski
et al 2006
Z AND LIGHT CURVE FOR THE OUTBURST AT 2000Z AND LIGHT CURVE FOR THE OUTBURST AT 2000
SHOCK IONIZATION ESTIMATIONSHOCK IONIZATION ESTIMATION
Date
(state of the system) μ
15.09.1999
(quiescence) 1.1222.11.2000
(outburst, rise to the second maximum) 1.00
06.12.2000 (outburst,
near maximum) 0.76
At the maximum of the outburst 24%
of the emission of nebulosity can be the result of the shocks formed.
VnnL
e α=μ
+
The ratio of the number of ionizing photons to recombinations
CONCLUSIONSCONCLUSIONS1) In quiescent state the accretion disk exists in the system.
2) The activity of symbiotics
depends strongly on stellar wind parameters. Namely, insignificant variations of the stellar wind parameters can lead to drastic changes in the the flow
structure, to the accretion
regime
change
over
and to the outburst.
So it is of interest to have precise estimates of wind parameters.
3) The collision of winds from both components results in the formation of the structure with shocks.
4) UV observations could give us the important information on the processes taking place in the system (particularly stellar winds from the components of the system) and thus to contribute to the study of the activity of symbiotic stars.
Thank you for your Thank you for your attentionattention!!
At present a very important role in astrophysics belongs to the numerical modeling of astrophysical processes. The reasons are:
►The rapid growth of computing facilities gives new opportunities for theoretical investigation.
►The necessity of interpretation of volume of observational data that grows continuously.
CONCLUSIONBasing on the detailed 3D gasdynamic
study of the
classical symbiotic system Z And we have studied the behaviour
of the system before the outburst and
during the outburst development.
UV observations could give us important information on the processes taking place in the system (particularly stellar winds from the components of the system) and thus to contribute to the study of the activity of symbiotic stars.
The
evolution
of
the
UV spectrum
throughout
the outburst
plays
a vital
role
in
distinguishing
between
the
outburst
models
currently
in
contention
for describing
outburst
behavior. Emission
line
strengths
of
the
FUSE-band
species, especially
when combined
with
lines
of
the
same
species
from
the
other
spectral
regions, provide
diagnostics
of
the colliding
windshock
region. Note
especially
that
FUSE provides
important
information
for
the
analysis of
the
x-ray
data
as
FUSE observations
of
HI
absorption
are
at
sufficiently
high
resolution
to
allow the
separation
of
the
interstellar
component
from
the
systemic
component
of
the
absorption.
Unlike
massive
binaries, the
winds
of
a symbiotic
system
have
very different
characteristics
--
the
hot
wind
is
very
thin
and
fast,
whereas
the
cool
wind
is
slow
and
weakly
ionized
-
and
hence
they can
be
isolated
spectroscopically.
The
white
dwarf
secondary
of
symbiotic
systems
provides
a far-UV continuum
source
against
which
absorption
from
a broad
range
of
ionization
levels
can
be
seen, ranging
from
molecular
hydrogen surrounding
the
giant
star
to
highly
ionized
material
in
the
wind
collision
region. Because
of
the
high
ionization
lines
arising
in
the hot
and
shocked
gas, as
well
as
the
molecular
and
atomic
absorption
arising
in
the
red
giants
extended
atmosphere, phase- resolved
spectra
provide
the
unique
tomographic
information
we
require
to
improve
our
knowledge
of
these
systems
and
how
winds are
generated
and
interact.
The
O vi
1032,1038 emission
lines
can
convert
into
broad
and highly
polarized
emission
lines
at
lambda
6825 and
lambda
7082 in
a Raman
scattering
process
by
neutral
hydrogen. From
a comparison of
direct
and
Raman
scattered
radiation
we
extract
new
information
on
the
scattering
geometry
in
symbiotic
systems. The
nebular
O vi emission
lines
are
in
all
objects
redshifted
by
about
+40 km
s(-1) .
This
can
be
explained
as
a radiative
line
transfer
effect
in
a slowly expanding
emission
region. A comparable
redshift
is
measured
in
the
Raman
scattered
O vi
lines. In
AG Peg
the
O vi
emissions
show beside
a narrow
nebular
line
a broad
component
from
a fast
stellar
wind
outflow. Many
interstellar
absorption
lines
of
molecular hydrogen
are
detected, particularly
near
the
O vi
lambda
1038
component. With
model
calculations
we
investigate
their
impact
on the
O vi
lines. From
the
dereddened
line
fluxes
of
the
direct
and
Raman
scattered
O vi
lines
we
derive
the
scattering
efficiency, which
is
defined
as
photon
flux
ratio
N_Raman/N_O VI. The
efficiencies
derived
for
RR Tel, V1016 Cyg
and
Z And
indicate
that about
30% of
the
released
O vi
lambda
1032 photons
interact
with
1. 1. v=v=20 20 кмкм//сс::►
Исследование
возможности
формирования
диска
►
Определение
величины
темпа
аккреции►
Проверка
соответствия
темпа
аккреции
диапазону
устойчивого
горения
2.2.
v=v=30 30 кмкм//сс::►
Определение
параметров
картины
течения
в
системе
без
диска
3.3.
v=v=2020→→30 30 кмкм//сс::►
Исследование
процесса
разрушения
диска
►
Рост
темпа
аккреции►
Достаточен
ли
рост
темпа
аккреции?
►
Достаточно
ли
долго
темп
аккреции
находится
за пределами
диапазона
стационарного
горения?
ВЫПОЛНЕННЫЕВЫПОЛНЕННЫЕ
РАСЧЕТЫРАСЧЕТЫ
V=80 км/cV=40 км/cV=20 km/s
The binary nature of these stars has been proved by A. Boyarchuk
in 1967 but later in 80th UV observations with
IUE confirmed the presence of the additional UV (more exactly far UV) radiation source.
Tomov
N. et al Astron.
Astrophys.,
v.401, p.669-676,
(2003)
More
than
100 years
of
observations
have
shown
that
Z And presents
outbursts.The
last
of
them
took
place
in
2000 and
has
been
actively
observed
at
different
wavelengths.
( ) ( )
22 21 2 2
1 2 1 22 2 2 2 2 21 2
12( )
GM GM Mx a yM Mx y z x a y z
⎛ ⎞⎛ ⎞⎜ ⎟Φ = − − − Ω − +⎜ ⎟⎜ ⎟+⎝ ⎠+ + − + + ⎝ ⎠
Roche potential
CONCLUSION
According to the results of gasdynamic
modeling of the flow structure in the classical symbiotic system Z And has been modeled.
The results of modeling show that transition to the outburst as well as behavior of the system during the outburst dpends
strongly on parameters of winds from components of a symbiotic system.
In order to carry out more detailed studies we needmore information on stellar wind parameters
The estimates of stellar winds parameters equires
UV observations
Показано, что
поэтапный
характер
роста
кривой
блеска
в период
развития
вспышки
может
быть
объяснен
в
рамках
модели
сталкивающихся
ветров
от
компонентов
системы. Предложен
сценарий
развития
вспышки
и
исследовано
возможное
влияние
изменений
в
структуре
течения
на
блеск системы. Моделируемые
изменения
светимости,
вызванные
формированием
системы
ударных
волн
DEPENDENCE OF THE FLOW DEPENDENCE OF THE FLOW STRUCTURE ON THE WIND VELOCITYSTRUCTURE ON THE WIND VELOCITY
The wind velocity regime is defined by the parameter
W=W=vvwindwind
/v/vorborb
(1).
Results of 3D modeling:
WW>1>1
–
wind accretion
WW<1<1
–
disk accretion.
Confirms earlier results .
In classical symbiotics
the value of giant’s wind velocity is close to the orbital velocity so both regimes are possible.
1Бисикало
и
др., 1994Бисноватый-Коган
и
др., 1979
In quiescent state accretion rate is within the steady burning range
At some moment accretion rate increases and oversteps the limits of the steady burning range.
The time scale of the accretion rate increase should correspond to thecharacteristic time of outburst development.
OUTBURST IN A CLASSICAL SYMBIOTIC SYSTEMOUTBURST IN A CLASSICAL SYMBIOTIC SYSTEM
What is the reason of the accretion rate What is the reason of the accretion rate growthgrowth??
Z AND LIGHTCURVE DURING THE OUTBURST IN Z AND LIGHTCURVE DURING THE OUTBURST IN 200200
Sokoloski
et al, 2004
In symbiotics:
WD has very small diameter as compared with the giant’s one so it observations at orbital phases where the white dwarf is located behind a portion of the cool wind would allow us to study different layers of the circumstellar
material.
Components have very different spectral characteristics and can be easily disentangled.
WD provides a bright UV continuum source upon which the absorption from the cool circumstellar
gas is superimposed. FUV
and UV ranges are very rich in resonance and diagnostically informative atomic and molecular transitions which would not be visible without presence of strong UV continuum.
В
настоящее
время, все
большую
роль начинает
играть
численноное
исследование
Симб
зв. Почему: 1) компьютеры;
2) Необходимость
интерпретации всевозрастающего
ОНД