The influence of stellar wind bubbles on the ionizing radiation field in HII regions
Stellar wind around starbursts forms cavities filled by hot gas with low density, thermalized by inverse wind shock. Young starbursts can contain the compact cavities inside Hii region. Diffuse ionizing radiation, that arises in the cavity could considerably affect the medium ionization. Outside the...
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Головна астрономічна обсерваторія НАН України
2012
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| Цитувати: | The influence of stellar wind bubbles on the ionizing radiation field in HII regions / I.O. Koshmak, B.Ya. Melekh // Advances in Astronomy and Space Physics. — 2012. — Т. 2., вип. 2. — С. 149-152. — Бібліогр.: 4 назв. — англ. |
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irk-123456789-1191882017-06-05T03:03:23Z The influence of stellar wind bubbles on the ionizing radiation field in HII regions Koshmak, I.O. Melekh, B.Ya. Stellar wind around starbursts forms cavities filled by hot gas with low density, thermalized by inverse wind shock. Young starbursts can contain the compact cavities inside Hii region. Diffuse ionizing radiation, that arises in the cavity could considerably affect the medium ionization. Outside the stellar wind bubble a thin dense shell formed by the direct wind shock is located. This shell can appreciably transform the shape of the ionizing radiation spectrum in neighbouring region. We investigate this possibility, using the density and temperature distributions of density and temperature, and other physical parameters of bubble-like structures given by Weaver et al. (1977). 2012 Article The influence of stellar wind bubbles on the ionizing radiation field in HII regions / I.O. Koshmak, B.Ya. Melekh // Advances in Astronomy and Space Physics. — 2012. — Т. 2., вип. 2. — С. 149-152. — Бібліогр.: 4 назв. — англ. 2227-1481 http://dspace.nbuv.gov.ua/handle/123456789/119188 en Advances in Astronomy and Space Physics Головна астрономічна обсерваторія НАН України |
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Stellar wind around starbursts forms cavities filled by hot gas with low density, thermalized by inverse wind shock. Young starbursts can contain the compact cavities inside Hii region. Diffuse ionizing radiation, that arises in the cavity could considerably affect the medium ionization. Outside the stellar wind bubble a thin dense shell formed by the direct wind shock is located. This shell can appreciably transform the shape of the ionizing radiation spectrum in neighbouring region. We investigate this possibility, using the density and temperature distributions of density and temperature, and other physical parameters of bubble-like structures given by Weaver et al. (1977). |
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Article |
| author |
Koshmak, I.O. Melekh, B.Ya. |
| spellingShingle |
Koshmak, I.O. Melekh, B.Ya. The influence of stellar wind bubbles on the ionizing radiation field in HII regions Advances in Astronomy and Space Physics |
| author_facet |
Koshmak, I.O. Melekh, B.Ya. |
| author_sort |
Koshmak, I.O. |
| title |
The influence of stellar wind bubbles on the ionizing radiation field in HII regions |
| title_short |
The influence of stellar wind bubbles on the ionizing radiation field in HII regions |
| title_full |
The influence of stellar wind bubbles on the ionizing radiation field in HII regions |
| title_fullStr |
The influence of stellar wind bubbles on the ionizing radiation field in HII regions |
| title_full_unstemmed |
The influence of stellar wind bubbles on the ionizing radiation field in HII regions |
| title_sort |
influence of stellar wind bubbles on the ionizing radiation field in hii regions |
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Головна астрономічна обсерваторія НАН України |
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2012 |
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http://dspace.nbuv.gov.ua/handle/123456789/119188 |
| citation_txt |
The influence of stellar wind bubbles on the ionizing radiation field in HII regions / I.O. Koshmak, B.Ya. Melekh // Advances in Astronomy and Space Physics. — 2012. — Т. 2., вип. 2. — С. 149-152. — Бібліогр.: 4 назв. — англ. |
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Advances in Astronomy and Space Physics |
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AT koshmakio theinfluenceofstellarwindbubblesontheionizingradiationfieldinhiiregions AT melekhbya theinfluenceofstellarwindbubblesontheionizingradiationfieldinhiiregions AT koshmakio influenceofstellarwindbubblesontheionizingradiationfieldinhiiregions AT melekhbya influenceofstellarwindbubblesontheionizingradiationfieldinhiiregions |
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2025-07-08T15:23:36Z |
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The in�uence of stellar wind bubbles
on the ionizing radiation �eld in Hii regions
I. O.Koshmak∗, B.Ya.Melekh†
Advances in Astronomy and Space Physics, 2, 149-152 (2012)
© I. O.Koshmak, B.Ya.Melekh, 2012
Ivan Franko National University of Lviv, Kyryla i Mefodia str., 8, 79005, Lviv, Ukraine
Stellar wind around starbursts forms cavities �lled by hot gas with low density, thermalized by inverse wind
shock. Young starbursts can contain the compact cavities inside Hii region. Di�use ionizing radiation, that arises
in the cavity could considerably a�ect the medium ionization. Outside the stellar wind bubble a thin dense shell
formed by the direct wind shock is located. This shell can appreciably transform the shape of the ionizing radiation
spectrum in neighbouring region. We investigate this possibility, using the density and temperature distributions
of density and temperature, and other physical parameters of bubble-like structures given by Weaver et al. (1977).
Key words: bubbles, evolution, HII regions
introduction
We intend to use multicomponent photoioniza-
tion modelling (PhM) for the studying of the in�u-
ence of embedded bubbles in Hii region surrounding
starburst on the changing of the ionization spectrum
shape. The �rst and second inner components of
such modelling correspond to the hypersonic stellar
wind zone and the region of shocked stellar wind re-
spectively. The distributions of the gas density and
temperature in these components are derived from
the bubble structure obtained from equations of con-
tinuity and energy transfer, including thermal con-
ductivity [4]. The third component is a thin shell
of high density gas formed by the wind shock. The
value of its density was obtained from isobaric con-
dition at contact discontinuity between the second
and third components. The fourth component is the
ordinary Hii region. Input spectrum of ionizing ra-
diation was obtained from the starburst model for a
wide range of ages and metallicity.
the method of calculations
The structure of the typical bubble is shown in
Fig. 1), where �a� is the hypersonic stellar wind, �b�
is the hot, almost isobaric region of shocked stellar
wind, �c� is the thin, dense shell of interstellar gas,
�d� is the typical Hii region.
For our multicomponent photoionization mod-
elling we used the following free parameters: age
of nebula t (varied from 1 to 10Myr), mass-loss of
starburst Ṁw (varied from 10−5 to 10−3M�/year);
velocity of stellar wind vw (varied from 20 to
2000 km/s), and density of interstellar gas n0 (varied
from 1 to 1000 cm−3).
0 2 4 6 8 10
0
2
4
6
8
10
Fig. 1: Structure of the typical bubble.
We used the Cloudy 08.00 code [1] for the pho-
toionization modelling, and the Starburst99 code
[2] for calculation of the energy distribution in ioniz-
ing spectrum (the so-called Lyc-spectrum) from the
starburst region. What is noteworthy, that each of
Lyc-spectra from the starburst region was calculated
at the corresponding model age. We modi�ed the
Cloudy 08.00 code for the realization of the multi-
component photoionization modelling.
Physical conditions along the radius of the stellar
wind bubble were determined as a solution of the fol-
lowing equations of continuity and energy transfer,
taking into account the thermal conductivity [4]:
1
ξ2
d
dξ
(ξ2u)− u− ξ
τ
dτ
dξ
=
22
21
, (1)
1
ξ2
d
dξ
(
ξ2τ
5
2
dτ
dξ
)
− 3
2
u− ξ
τ
dτ
dξ
=
13
35
. (2)
∗ihorkoshmak@gmail.com
†bmelekh@gmail.com
149
Advances in Astronomy and Space Physics I. O.Koshmak, B.Ya.Melekh
The �b� shell has internal R1 and external R2
radii, respectively:
R1 = 5.7Ṁ0.3
6 n−0.3
0 v0.12000t
0.4
6 [pc],
R2 = 27Ṁ0.2
6 n−0.2
0 v0.42000t
0.6
6 [pc], (3)
where Ṁ6 =
Ṁw
10−6
, v2000 =
vw
2000
, t6 =
t
106
; τ and u
are dimensionless variables which are functions only
of a dimensionless radial coordinate ξ =
r
R2(t)
.
The density of the third component ns was ob-
tained from the isobaric condition at contact discon-
tinuity between the second and third components.
We calculated thickness of the third component us-
ing the following expression [3]:
∆r = R2
{(
1− n0
ns
)− 1
3
− 1
}
[pc]. (4)
In our case, the electron temperature can be de-
termined in two ways: (1) from the energy balance
equation in photoionization modelling, and (2) from
the hydrodynamic model of the bubble.
The �rst way was used to calculate of the electron
temperature values in �c� and �d� components. But
the temperature in �a� and �b� components was ob-
tained using the second way, because in these cases
it is de�ned mainly by hydrodynamic processes.
For our investigations we used the hydrodynamic
model of the stellar wind bubble from [4]. Thus, the
boundary conditions are the same as in [4]. The mul-
ticomponent model grid and its free parameters were
obtained in accordance with the parameters of the
bubble (mass-loss rate of the starburst, velocity of
the stellar wind, age of the nebula). Thus, grid free
parameters de�ne the size of the bubble and physical
conditions therein.
The radial distributions of gas density and tem-
perature in the stellar wind bubble are given by the
following approximate expressions:
nH = DF · 10An(R), Te = TF · 10AT (R), (5)
where DF = n
19
35
0 · (Ṁ6 · v22000)
6
35 · t−
6
35
6 , TF =
n
2
35
0 · (Ṁ6 · v22000)
6
35 · t−
22
35
6 , An(R) = log na(R) and
An(R) = log nb(R), AT (R) = log T (R) are the ap-
proximate expressions obtained as �ts of the results
from [4]:
log na(R) = −3.82495+
+ 1.00971e−
R+0.17442
0.25075 + 2.5191e−
R+0.17442
1.94557 ,
log nb(R) = 64.03901471− 48.80541204 ·R+
+13.97542937·R2−2.11750182·R3+0.18978405·R4,
− 0.01042102 ·R5 + 3.44806684 ·R6−
− 6.31658041 · 10−6 ·R7 + 4.9239613 · 10−8 ·R8,
(6)
R = 0.005÷ 6.205[pc]; log Tfit1(R) = 4.64;
R = 6.205÷ 9.205[pc]; log Tfit2(R) = 5.84892+
+ 2.83179 · (1− e−
R−6.11145
0.25075 )0.49234 · e−
R−6.11145
3.48938 ;
R = 9.205÷ 22.505[pc];
log Tfit3(R) = −6.429060955 + 6.299770486 ·R−
− 1.157442226 ·R2 + 0.10650819 ·R3−
−0.005318678·R4+0.000138352·R5−0.000001474·R6;
R = 22.505÷ 27[pc];
log Tfit4(R) = −1912462.460571898+
+ 472743.449417495 ·R− 48663.85822284 ·R2
+ 2670.237186899 ·R3 − 82.372465048 ·R4+
+ 1.354511416 ·R5 − 0.009275676 ·R6. (7)
Expressions (6) and (7) are obtained for typi-
cal bubble with R1=5.7 pc and R2=27pc and were
rescaled to the corresponding bubble size for each of
the grid models (see Figs. 2, 3).
0 5 10 15 20 25 30
-4,0
-3,5
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
lo
g 10
n,
m
-3
R, pc
Fig. 2: Figure is based on approximation expression of
distribution of density, (6).
Models of all components were calculated sepa-
rately. But ionizing radiation propagates from the
central starburst region in outward direction through
150
Advances in Astronomy and Space Physics I. O.Koshmak, B.Ya.Melekh
the bubble components. Thus, for an example, pho-
toionization in �d� component is caused by ionizing
photons with energy distributed di�erently than that
in Lyc-spectrum calculated using the Starburst99
code [2], because the shape of the photon energy
distribution has been transformed in components it
passed through. As it also was mentioned above, the
density in third component was obtained from iso-
baric condition at contact discontinuity between the
second and third components. Hence, the physical
conditions in the third component depend on those
in the second component.
0 5 10 15 20 25 30
3,8
4,0
4,2
4,4
4,6
4,8
5,0
5,2
5,4
5,6
5,8
6,0
6,2
6,4
6,6
6,8
7,0
lo
g 1
0T
,K
R,pc
Fig. 3: Figure is based on approximation expression of
distribution of temperature, (7).
results and conclusions
The evolution grid of multicomponent photoion-
ization models with di�erent bubble parameters was
calculated. The contribution of the stellar wind bub-
ble components to the changes of the energy distri-
bution shape in ionizing spectrum (Lyc-spectrum)
was analysed. We identi�ed three types of this ef-
fect: without the lack of quanta beyond the Lyman
limit (1Ry) (Fig. 4), with the lack of quanta beyond
the Lyman limit (this lack was formed by the third
component) (Fig. 5), and partial case with the lack of
quanta beyond the Lyman limit when bubble forms
the excess of quanta (Fig. 6). The excess of quanta
appears due to contribution of the second compo-
nent that emits quanta excess beyond 5-6Ry (com-
paring with the input Lyc-spectrum, calculated using
Starburst99 code [2]).
This excess mainly reveals in models with the age
larger than 5Myr. Such old bubbles should be very
extended (hundreds of parsecs). Therefore at this
age the excess is not caused by the stellar ionizing
emission and the presence of massive O and B stars
is not a necessary condition for its appearance.
Fig. 4: Type without lack of quanta beyond Lyman-
continuum limit.
Fig. 5: Type with lack of quanta beyond Lyman-
continuum limit (this lack was formed by third com-
ponent).
Fig. 6: Partial case with lack of quanta beyond Lyman-
continuum limit when bubble forms the excess of quanta.
One can see that the gap in spectrum within en-
151
Advances in Astronomy and Space Physics I. O.Koshmak, B.Ya.Melekh
ergy range 1-4Ry arises in Lyc-spectra if photons
propagate through the thin dense envelope. That
is due to the fact that photons energy dependence
of the cross section, σν , for hydrogen-like ions has
a peak at its ionization potential, and then rapidly
decreases with increasing of the photons energy. In
the case of high density envelope the free path of
photons in environment with density n is de�ned as
lν = 1/(σνn), hence photons with the energy close to
the ionization potential will be absorbed, while those
with higher energy will escape from such envelope.
acknowledgement
The research presented in this publication was
supported by grant 0111U001087 of the Ukrainian
National Foundation of Fundamental Researches.
references
[1] FerlandG. J. 2005, `Hazy, A Brief Introduction to Cloudy
05.07, University of Kentucky Internal Report'
[2] LeithererC., SchaererD., Goldader J.D. et al. 1999,
ApJS, 123, 3
[3] Vallee J. P. 1993, ApJ, 419, 670
[4] WeaverR., McCrayR., Castor J., ShapiroP. & MooreR.
1977, ApJ, 218, 377
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