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ROSEリポジトリいばらき (茨城大学学術情報リポジトリ)
Title Notes on Time Variations of Gas Flow in Seven GlobularClusters
Author(s) Tanaka. Yasuo / Sunaoshi. Misako
Citation 茨城大学教育学部紀要. 自然科学(28): 13-24
Issue Date 1979-03
URL http://hdl.handle.net/10109/11222
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Bull. Fac. Educ., Ibaraki Univ.(Natural Sciences), No.28(1979),13-24 13
Notes on Time Variations of Gas Flow
in Seven Globular Cluste路
Yasuo TANAKA and Misako SUNAOSHI*
丑葛Cぬy(ガE伽α’めπ,∬6αrα窺U励erε砂
雌‘・310,∫αPαη
(Received October 17,1978)
Abstract
Gas flows in actual model clusters are illustrated in figures where the
effect of heating by ultraviolet radiation is taken into account. There are
three typical flows, that is, entirely outward flows, weak inflows in a limited
region, and rather strong partial inflows within a stagnation point. The de一
pendence of gas且ows upon structural paramcters of the clusters is discussed
in comparison with the initial temperature and density, the temperature and
After the discovery of the discrepancy between the observed and computa一
tionally estimated amounts of hydrogen gas in globular clusters(Knapp et al.,
1973)and especially of the X-ray emissions from clusters(Giacconi et al.,1974),
the behavior of gas in globular clusters is studied by many authors(Scott and
Rose,1975, VandenBerg Imd Faul㎞er,1977, and Tanaka et al.,1978 hereafter
referred to as Paper I). The numerical calculations have been carried out by Scott
and Rose(1975)for isothermal steady outnows and by Faul㎞er and
(1977)for steady out且ows where the effOct of radiative cooling is taken into
account. Time-dependent numerical solutions of gas f[ow in rather compact
globular clusters are fi聡Uy obtained by VandenBerg and Fau1㎞er(1977). In
Paper I, gas flows in actual model clusters are analyzed and also the effect of heat一
ing by ultraviolet radiation is discussed. However, the time variations of gas flows
in only two typical clusters were illustrated in Paper L We like to supplement the
behaviors of gas with time iロthe remaining seven clusters in this note. We will
discuss the dependence of gas flows upon the structural parameters of clusters and
sketch the plan for further detailed studies.
We summ曲e theおs㎜ptions㎝d pr㏄edures for nume翻computationshere, since the details are given in Paper I. Adopted clusters are NGC 1851,1904,
* Present address, Business Consultant CooP., Shinjuku, Tokyo 160, Japan.
14 Bull. Fac. Educ。, Ibaraki Univ.(Natural Sciences), No.28(1979)
6266,6541,6712,6715and 6752 for which七he structural parameters are speci一
fied mainly following Peterson and King(1975). Those are the core radius R c, the
logarithm of the ratio of the tidal radius of clusters to the core radius C, the
central density of stars ρ*c, and the dispersion velocity of stars 7*・Then the
density distribution of stars is obtained by using the parameters・Stars in the stage
of transition from七he red giant branch to horizontal branch are assumed to eject
gas into clusters and to distribute spatially in a cluster. The gas flows are deter一
mined by the disribution of gravity, mass loss rate from stars and energy supply
and loss. The energy supply and loss are refered to Mathews and Baker(1971)
who take the heating by ultraviolet radiation into account. The basic equations
for gas flow are solved by the beam scheme method(Sanders and Prend6rgast,
1974)by using HITAC 8700/88000f the University of Tokyo from the Mito
Branch of the Computer Center, Ibaraki University.
The computed results of the time-variations of the velocity distribution, of
the temperature distribution and of the density distribution are shown in the
figures. The characteristics of gas flows in the adopted clusters are as follows.
(1》 NGC 6715
This cluster belongs to the group of clusters with large values of C,7*and
ρ*c.The velocity distributions vary with time since gas ejected from stars is
assumed to be rest at the initial廿me step,104 years, as shown in Fig.1-a. The
radius of the stagnation point within which gas flows inward increases slightly
with time. The maximum velocity of the partial inflow also,increases and becomes
aconstant v訓ue of 4㎞/sec. A compression wave genera加d at the center pro・
pagates outwardly as seen on七he curve denoted as A in Fig.1-a After 12×107
years, the velocity distribution remains unchanged. Although the temperature of
gas is initially spatially constant value of 2070°K, the central temperature in・
creases with time, whereas the temperature decreases in the outer region after the
・・mp・essi・n wave h鎚passed. The cent・組d・n・ity・f gas incre肥・・f・・m 4×10-26
9/cm3 at 104 years to 1.2x10-2591cm3,as seen in Fig.1-c.
(2} NGC 1851
This cluster has the largest values of C and ρ*c, but it is noted for the
cluster to be smaller Rc and 7*than those for NGC 6715. The position of the
stagnation point is hardly changed in Fig.2-a. The maximum inflow velocity
increases in the absolute value, but is not surely recognized after 5×106 years
because of rough spatial gdds near the center. A compression wave propagates
and causes small disturbances on the curves in Fig.2-b. The initial temperature is
of 1700°K at 104 years. The behaviors of gas temperature and density with time
are similar to those fbr NGC 6715. However, the central density becomes 5.2×
Tanaka&Sunaoshi:Time Variations of Gas Flow l5
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22 Bull. Fac. Educ., Ibaraki Univ.(Natural Sciences), No.28(1979)
Table I. Ranking for structural parameters and physical quantities
of flow in the order of magnitude.
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)(11)(12)
NGC Cρ*c 7・ φ Tcilρ・i R・fρ・f T・f 7mf1851 1 1 3 2 1 3 1 3 3 1 1 2
1904 7 7 7 7 7 7 7 - 7 7 - 7
2419 9 9 9 9 9 9 9 - 9 9 - 9
6266 6 4 4 4 4 4 3 5 4 4 4 4
6541 2 5 5 5 4 5 5 4 5 5 4 5
6712 8 8 8 8 8 8 8 - 8 8 - 8
6715 5 2 2 2 3 2 2 2 2 2 3 3
6752 4 6 6 6 6 6 6 - 6 6 - 6
7078 3 3 1 1 2 1 3 1 1 2 2 1
10-249/cm 3 at 2.6×107 years from 5.3 x 10-269/cm 3 at 104 years.
《3) NGC 6266 」shis cluster falls in the group of clusters with mediate values of C.However,
the central stellar density and 7*ale rather high. From Fig.3-a, it appears that
the region of inflow is limited in O.5 pc〈R<1.2pc, which is almost constant
with time. The initial temperature is of 1600°K. The central density of gas valies
from the initial value of 3.4×10-269/cm 3 to 2.O x 10-249/cm 3.
(4} NGC 6541
It should be noted that this cluster has a large value of C following NGC 1851.
However, the limited region of inflow is nallower than for NGC 6266. The initial
central temperature and density are 1030°K and 2.1x10-26 9/cm3,respectively.
Abump on the curve of B in Fig.4-b is caused by ashock wave to which the
compression wave has grown up. After 2×107 years, the flow remains unchanged
in all distributions of velocity, temperature and density.
{5} NGC 6752, NGC 1904 and NGC 6712
These clusters have low values of ρ*c and 7*. NGC 6752, however, has the
nearly same value of C as that for NGC 6715. The values of C,ρ*c and 7*for
NGC 6712 are the lowest among the clusters adopted here. The value of C for
NGC 6712 is chosen tentatively, because of a lack of the observation on the tidal
radius of this cluster. The time-vahations are given in Fig.5,6 and 7 for NGC
6752,1904and 6712, respectively. Gas f[ows entirely outward in these clus ters.
Tanaka&Sunaoshi:Time Variations of Gas Flow 23
Table II. Choice of stmctural parameters for further studies.
R,(P・) C ρ*c(M。/P・3) 7・(km1・ec)
0.5 2.2 1×105 15
1.0 2.0 4×104 10
2.0 1.5 1×104 5
1.0 4×102
4×100
The only f[ows after the compression waves have passed through the clusters are
shown in each figure of(a). The initial temperatures are very low such as 790,520
and 440°K for NGC 6752,1904 and 6712, respectively. The central density is also
increased by several ten times of the initial values of 10-26,5x10-27 and 2×
10-2791cm3 for NGC 6752,1904 and 6712, respectively.
The且ows in NGC 7078 and 2419 should be referred to Paper 1. Although
NGC 7078 and 6712 are seemed to coincide with X-ray sources, it is interesting
that the pattem of flows differs in each other. In order to study the relation of
the structur訓parameters to the char㏄teristics of now, we rank the p鑓㎜eters
and physical quantities of flows in Table I, including NGC 2419 and 7078. The
central gravitational potential of clusters, the central temperature, the stagnation
point are denoted in Table I asφ,Tc,ρc,7m and R s,respectively. The su鮒xes
of i and f represent the initial time and the time when flow becomes nearly
steady. We give also the ranking by the simple mean for the columns of(1)to(4)
in the fifth column and that for the col㎜ns of(6)to(12)in the twelveth
column.
From Table.1,it is seen that small values of the parameters represent well the
feature of jユow with which clusters have entirely outward且ows. However, in the
clusters with partial inflow in a limited region, it seems that the individual para.
meter takes part in the property of flow. That is,ρ*c seems to relate to ρci,
Tcf and 7mf, while 7*andφare responsible to Tci, R sf and ρcf・These, how一
ever, are rather qualitative because our present aim was computations of flow in
actual cluster models. Thus, further calcし皿ations are desired with the choice of
parameters as shown in Table II in order to reveal the relation between structural
parameters and charactehstics of flows in clusters with partial且ows.
The authors ale indebted to Mr. Y. Hirayama for the aid of modifソing his
program in the beam scheme for flows in創obular clusters.
24 Bull. Fac. Educ., Ibaraki Univ.(Natural Sciences), No.28(1979)
References
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