恒星進化の理論の現状とアストロメトリ

『高密度アストロメトリ観測時代を迎えた２１世紀の天文学』
（国立天文台、Sep. 19-20、 2007）
恒星進化の理論の現状とアストロメトリ
藤本正行
須田拓馬・勝田豊（北大理）
小宮悠（東北大理）
contents
1. Parallaxes ⇒ 距離 ⇒ 光度 + spectroscopy
→ 恒星の半径、表面温度、質量、組成
⇒ Age-Metallicity relation
⇒ star formation history of solar neighborhood
2. 恒星進化の理論的課題
–
–
Mass Loss
Internal (Extra) Material Mixing
～ convective overshooting
非球対称効果（rotation, magnetic fields)
3. 銀河系の構造・進化への探査手段としての恒星
–
–
惑星を持つ恒星（Planet Hoboring Stars PHS）
銀河系ハロー星（Extremely Metal-Poor Stars EMP, UMP, EMP）
１．HR diagram from Hipparcos
Hyades
near-by stars
Model fitting
(Perryman et al. 1998, A&Ap)
ZAMS:
Metallicity and effective temperature
from high resolution spectroscopy: [Fe/H]= 0.14
Solar mixing length: l=1.64
resultant helium abundance: Y = 0.26
Isochrones: Age 625 ±50 Myr
Asplund, Grevesse & Sauval . (2004)
Decrease of metal abundance in solar by
almost a factor of two as compared with a
compilation by Anders & Grevesse (1989)
Physical parameters
for Evolved stars
(de Silva et al 2006 A&A)
Mass-metallicity relation
Age-metallicity relation
Color-Magnitude Diagram
Star Formation History
of solar neighborhood
CMD of near-by
stars
SFR vs. Age
with the evolutionary models
Luminosity
Function
(Cignoni et al 2006 A&A)
2. 恒星進化の理論的な課題
2.1 mass loss
１） Massive Stars
⇒ Supernova
neutron stars
black hole
２） Intermediate- & Low-mass Stars
⇒ white dwarfs
2.1.a Mass loss from Massive Stars
by the central exhaustion
of helium
wind
mass loss
Wolf Rayet
WNL
WC
Limongi ＆ Chieffi （2006）
SN Explosions
Core Mass at SNe
ηcarina (binary)
VY Cannis Majoris
Wolf-Rayet Stars
WR124
WR１０４ (binary)
2.1.b Low- & Intermediate mass
stars -- from AGBs to PNe and to WDs
Fast wind
Hydrogen deficient
CSPNe ~20%
Born-again AGB
Ignition of Very Late
Thermal Pulse
Super wind
Wind
mass
loss
Hydrogen is mixed and burnt
by He-flash convection
Non-DA (hydrogen deficient)
WDs ~20%
Herwig 2005, ARA$AP
End of Low- and Intermediate –
mass stars
Cat Eye
Planetary Nebulae
X-ray from PNe
Guerrero, Chu & Gruendl
Mem. S. A. It. 76,446 (2005)
Suzaku observation of
BD+30°3639
Murashima, Kokubun, Makishima et al. 2006, ApJL,647, L131
村島未生、天文学会2006年春季年会講演
X-ray spectra from BD +30°3639
Large
enhancement of
C and Ne
XIS-1 spectra
background
Spectra with the solar
abundance ratio
Fast wind ejects the
matter from the
Helium Flash
Convective Zone
Empirical Mass Loss Rates
Reimers formula (1977)
Nieuwenhuijen & Jager (1990)
Fast wind
Mass Loss Theory (Massive Stars)
Radiation Pressure (Line-Driven)
+ Multiple Scattering
eg.,
(A&A, 2000)
may subject to Large overestimation
by Clumps in Wind (Bouret etal. A&A 2005)
Foullerton et al. ApJ 2006
(mass loss
rate ∝d1.5)
Mass Loss Theory; Cool stars
Pulsation-driven wind model
+ Radiation Pressure on Dusts
But, for Oxygen-rich Chemistry;
Shortage of radiation
pressure on dusts (Woitke A&A, 2006)
Carbon-rich Chemistry
(Watcher et al. A&A, 2002)
+Superwind
+AGB
RGB
Large Mass Loss
at Later Stages
Reimers formula
Mira variables
L  104 L , R  102 R
Fast wind
L  104 L , R  102 R 4
L  10 L , R  102 R
(Pulsation period)
R  1R
Lawlor & MacDonald 2006
2.2 Mixing in Stars
Current standard framework =
spherical symmetry + thermal convection +
chemical diffusion
(mixing length theory)
Rotation, magnetic fields
⇒ instabilities = turbulence
⇒ transport of Angular momentum
+ internal material mixing
Results
Surface metal pollution shifts the evolutionary track to
the lower effective temperature.
Polluted: Z=0.02 at interior,
Z=0.04 at Surface convection
0.8Msun
Z=0.04
Log (L/Lsun)
Z=0.02
1.0Msun
log Teff
He enriched model
Log (L/Lsun)
1.01
1.09M
0.90M He enriched
1.00M Basic model
Z=0.04, homogeneous
ZAMS for He-enriched model
ZAMS for Basic model
log Teff
Mixing-length enlarged model
1.09M
Log (L/Lsun)
1.10M
1.00M Basic model
0.98M Mixing-length enlarged
ZAMS for Basic model
ZAMS for Mixing-Length enlarged model
log Teff
Age of changed free-parameter models [Gyr]
Ages of basic model and other models
He enriched
Mixing-length enlarged
1:1
Age of the basic model [Gyr]
Ages of He enriched
and large mixinglength models are
underestimated if
treated as a basic
model.
3. Stellar Evolution as a Probe
3.1 PHS with Hot Jupiters
Stars without
planets
PHS
Extra-solar planets discovered
質量の分布
（１MJUP ＝木星の質
量）
軌道半径と離心率
（１AU=地球の軌道半径）
○惑星の母星
恒星の金属量
[Fe/H]=log10 X (Fe) / X (H)
 log10 X (Fe) / X (H ) sun
Arguments against
Metal-Pollution
No-correlation with the depth
of surface convection
Pollut
ed?
No or weak
correlationｓ
with the
condensation
temperatures
Ecuvillon et al. (2006)
Giants with Planets
Planets with Giants are metal-poorer
than those with Dwarfs (Pasquini et al. 2007)
＆
Metallicity Distribution
Giant PHSs (G and K)
Dwarf
PHSs
Metal-Age relation
Possible explanations
1) Formation mechanism
depending on the
mass of host stars
2) Metal dependence of
Migration: metal-rich
host  smaller orbits
3) Surface pollution
∵ dilution due to deep
surface convection
3.2 Stars in the Galactic Halo
Deep survey of metal-poor stars in the Galactic Halo:
HK survey （Beers et al. 1992） [2800 deg2 (North) + 4100 deg2 (South),
11.0 < B < 15.5 ]
Hamburg/ESO (Christlieb et al. 2000) [8225 deg2 (South), 10.0 < B < 17.5 ]
[Fe/H]<-2の星 ~2700個
[Fe/H]<-3の星 ~400個
(Beers et al. ARA&Ap 2005)
2 stars below [Fe/H] <-5, HE0107-5240 （-5.3, 2003)
HE1327-2426 (-5.4, 2005)
1 star between [Fe/H] = -4 ~-5
HE0557-4840 (-4.8, 2007)
number
10000
effective yields
1000
HK
100
HAM/ESO
10
1
~ -5
-5 ~ -4
-4 ~ -3
[Fe/H]
Beers & Christlieb (2005) + Norris et al. (2007)
-3 ~ -2
3.2.1 EMP population のIMF と
Binary origin （Komiya et al. 2007）
Mmd=10 M, Δm=0.4とすると
mξ(m)
主星のIMF
白色矮星
+CEMP
超新星
鉄, r-process
元素合成
伴星のIMF
EMP starとして残る
低質量星
0.1
中質量星
1
大質量星
10
m (M)
100
Binary ― Probe into missing more massive
EMP stars―
C,O
He
H
H
Evolution of a
primary star affects
abundances of a
secondary star.
CEMP star is formed in a binary system.
Observed feature of a CEMP star
Mass of a primary star.
Estimate of
the IMF
2種類のCEMP
CEMP-s
3
CEMP-nos
[Ba/Fe]
s-process元素過剰
窒素も過剰
s-process元素は少
ない
窒素は過剰な星と
過剰でない星があ
る
CEMP-s
2
1
CEMP-nos
0
-1
-2
-1
-0.5
（EMPではない炭素星は1種類）
0
0.5
1
1.5
2
□：[C/Fe], ■:[N/Fe]
2.5
3
3.2.2 Metallicity Distribution
Function (MDF)
100000
Number
nunmber
Assumptions
One zone model.
No infall/outflow.
Instantaneous
recycling.
Fe yield: 0.07M☉
Salpeter IMF
10000
10000
Theoretical MDF
for IMF with
Mmd =10 M☉.
1000
1000
100
Hyper
metal
100
poor (HMP)
10
10
stars
Cut-off
of MDF
observation
11
Results
Derived top-heavy IMF is
consistent with observation
(for [Fe/H] > -4).
-6
-6
-5.5
-5
-5
-4.5
-4
-3.5
-4
[Fe/H]
[Fe/H]
-3
-3
-2.5
-2
-2
銀河形成
Population III
形成
2段階に分けて考える
EMP形成
[Fe/H]=-4~-2.5
mstar~10M☉
合体
MDM~106M☉
Mgas~105M☉
最初は小さなガス雲の中で
星形成が起きる
現在：Population I
disk形成。 Population II形成
Mgas~1011M☉
Hierarchical galaxy formation
• The cut-off is originate from structure formation
process
[Fe/H]~-4
2nd star
[Fe/H]~-4
SN
1st mini-halo
~ 106-7 M☉
After 1st SN explosion,
M Fe
0.07
Z
 6
 104 Z solar
M cloud 10 baryon
MDF cut-off at [Fe/H]~-4
Pop.3 stars still alive ⇒HMP star.
(Suda et al.2004)
merge
Merger tree
mini-haloの
質量(M☉)
（実際は枝の数
はこの1000倍）
このようなtree
での化学進化
を計算
0.1
0.2
( Big Bangからの時間Gyr)
0.5 1
z
Effect of structure formation
Assumptions
Merging history:
Press-Schechter
(Somerville &
Kollat1999)
Theoretical
MDF with
merger tree.
SFE: 10-10/yr
Observed
MDF
Results
Model predict cutoff at [Fe/H]~-4.
Number of stars
with Z = 0 is
inconsistent.
First star
Mmd =100 M☉ for Z=0.
Pair-Instability supernovae
(Fe yield: 10M☉)
⇒iron overproduction
First star : supermassive
not PISN.
初代星への表面汚染
• Mini-haloの中では恒星の運動速度が遅いために、
星間ガスの恒星表面への降着が起きやすい
金属0で誕生
周囲の星間
物質を降着
[Fe/H]~-3
連星の場合は主星か
らの質量降着
（炭素星に）[Fe/H]<-5
赤色巨星に
[Fe/H]<-5
汚染を考慮したMDF
3.3.3 Database of Galactic EMP Stars
for Galactic Archaeology
(DaGaAr: Suda et al. 2007)
Contents
• Papers: 96 (covering since 2000)
• Stars:
• Data
on high resolution spectroscopy
[Fe/H] Number(prev.)
1495(847)
[X/Fe]: 24,498
[X/H]: 26,090
logε: 26,090
Ｌog g, etc; atmospheric data,
-1<
124
-1~-2 214
-2~-3 419
-3~-4 117
<-4
4
Sample characteristics
Metallicity
distribution
giants
Magnitude distribution
among samples
selection effects
due to survey
Teff - surface
gravity
dwarfs
Eu: neutron
r-process
+ s-process
[Eu/Fe]
capture element
r-process only
[Eu/Ba] > 0
[Fe/H]
Space distributions of EMP stars
Distance ← surface gravity (assuming M=0.8 M)
Astrometry
＋
Spectroscopy
(e.g., WFMOS）
↓
位置、運動、
光度、組成 ⇒ 年齢
dwarfs
giants
銀河の恒星地図
銀河形成史の再構築

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