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）

『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）

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, EM

P ）

１． HR diagram from Hipparcos

near-by stars

Hyades

Model fitting (Perryman et al. 1998, A&Ap)

ZAMS:Metallicity and effective temperature

from high resolution spectroscopy: [Fe/H]= 0.14Solar mixing length: l=1.64

resultant helium abundance: Y = 0.26Isochrones: 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

(Cignoni et al 2006 A&A)

CMD of near-by stars

LuminosityFunction

SFR vs. Agewith the evolutionary models

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

Wolf Rayet WNL

WC

Limongi ＆ Chieffi （ 2006 ）

wind mass loss

by the central exhaustion of helium

SN ExplosionsCore Mass at SNe

ηcarina (binary)

VY Cannis Majoris

Wolf-Rayet Stars WR124

WR １０４ (binary)

2.1.b Low- & Intermediate mass stars -- from AGBs to PNe and to WDs

Born-again AGBIgnition of Very Late Thermal Pulse Hydrogen is mixed and burnt by He-flash convection

Fast wind Super wind

Hydrogen deficientCSPNe ~20%

Non-DA (hydrogen deficient)WDs ~20%

Herwig 2005, ARA$AP

Wind mass loss

End of Low- and Intermediate –mass stars

Cat Eye Planetary Nebulae

X-ray from PNe

Guerrero, Chu & GruendlMem. 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

Large enhancement ofC and Ne

Fast wind ejects the matter from the Helium Flash Convective Zone

X-ray spectra from BD +30°3639

XIS-1 spectra background

Spectra with the solar abundance ratio

Empirical Mass Loss Rates

Reimers formula (1977)

Nieuwenhuijen & Jager (1990)

Fast wind

Mass Loss Theory (Massive Stars)

(A&A, 2000)

Radiation Pressure (Line-Driven)

+ Multiple Scattering

may subject to Large overestimation by Clumps in Wind (Bouret etal. A&A 2005)

Foullerton et al. ApJ 2006

(mass loss rate d∝ 1.5)

eg.,

Mass Loss Theory; Cool starsPulsation-driven wind model

+ Radiation Pressure on DustsCarbon-rich Chemistry

(Watcher et al. A&A, 2002)

But, for Oxygen-rich Chemistry; Shortage of radiation pressure on dusts (Woitke A&A, 2006)

RGB

+Superwind

+AGB

Large Mass Loss at Later Stages

4 210 , 10L L R R

4 210 , 10L L R R

Reimers formula

Mira variables

Fast wind

Lawlor & MacDonald 2006

1R R 4 210 , 10L L R R

(Pulsation period)

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

1.0Msun

0.8Msun

log Teff

Log

(L

/Lsu

n)Surface metal pollution shifts the evolutionary track to the lower effective temperature.

Z=0.02

Polluted: Z=0.02 at interior,Z=0.04 at Surface convection

Z=0.04

He enriched model

0.90 He enrichedM

1.01

1.00 Basic modelM

1.09M

Z=0.04, homogeneous

ZAMS for Basic modelZAMS for He-enriched model

log Teff

Log

(L

/Lsu

n)

Mixing-length enlarged model

1.00 Basic modelM

1.09M

0.98 Mixing-length enlargedM

1.10M

ZAMS for Basic modelZAMS for Mixing-Length enlarged model

log Teff

Log

(L

/Lsu

n)

Ages of basic model and other models

Age of the basic model [Gyr]

Age

of

chan

ged

free

-par

amet

er m

odel

s [G

yr]

Ages of He enriched and large mixing-length models are underestimated if treated as a basic model.

He enriched

Mixing-length enlarged

1:1

3. Stellar Evolution as a Probe3.1 PHS with Hot Jupiters

PHS

Stars withoutplanets

Extra-solar 　 planets 　discovered

質量の分布 軌道半径と離心率

（ １ AU= 地球の軌道半径）（１ MJUP ＝木星の質量）

○ 惑星の母星

10

10 sun

[Fe/H]=log (Fe) / (H)

log (Fe) / (H )

X X

X X

恒星の金属量

Arguments against Metal-Pollution

Polluted?

Ecuvillon et al. (2006)

No-correlation with the depthof surface convection

No or weak correlation ｓ with the condensation temperatures

Giants with PlanetsPlanets with Giants are metal-poorer than those with Dwarfs (Pasquini et al. 2007)

Metallicity Distribution ＆ Metal-Age relation

Giant PHSs (G and K)

Dwarf PHSs

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 HaloDeep 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)

~ -5 -5 ~ -4 -4 ~ -3 -3 ~ -21

10

100

1000

10000

num

ber

[Fe/H]

effective yields

HK

HAM/ ESO

Beers & Christlieb (2005) + Norris et al. (2007)

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)

3.2.1 EMP population の IMF と Binary origin （ Komiya et al. 2007 ）

EMP star として残る

白色矮星 +CEMP 超新星

鉄 , r-process 元素合成

低質量星 中質量星 大質量星

主星の IMF

伴星の伴星の IMFIMF

Mmd=10 M, Δm=0.4 とすると

mξ(m)

m (M)0.1 1 10 100

Binary Binary ― Probe into missing more massive ― Probe into missing more massive EMP stars―EMP stars―

H

C,O

H

He

Estimate of the IMF

CEMP star is formed in a binary system.

Evolution of a primary star affects abundances of a secondary star.

Observed feature of a CEMP star

Mass of a primary star.

2 種類の CEMP

CEMP-s

s-process 元素過剰窒素も過剰

CEMP-nos

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（ EMP ではない炭素星は 1 種類）

[Ba/

Fe]

-1 -0.5 0 0.5 1 1.5 2 2.5 3

□ ： [C/Fe], ■:[N/Fe]

3

2

1

0

-1

-2

CEMP-nos

CEMP-s

3.2.2 Metallicity Distribution Function (MDF)

Derived top-heavy IMF is consistent with observation (for [Fe/H] > -4).

One zone model.No infall/outflow.Instantaneous recycling.

Fe yield: 0.07M☉

1

10

100

1000

10000

100000

-6 -5.5 -5 -4.5 -4 -3.5 -3 -2.5 -2

nu

nm

be

r

[Fe/H]

Number

10000

1000

100

10

1

[Fe/H]

Salpeter IMF

Theoretical MDF for IMF with Mmd

=10 M .☉

observation

Hyper metal poor (HMP) stars

Cut-off of MDF

Assumptions

Results -6 -5 -4 -3 -2

MDM~106M☉

Mgas~105M☉

[Fe/H]=-4~-2.5 mstar~10M☉

銀河形成

現在： Population I

最初は小さなガス雲の中で星形成が起きる

Population III形成

Population II 形成 Mgas~1011M☉

disk 形成。

EMP 形成

2 段階に分けて考える

合体

Hierarchical galaxy formationHierarchical galaxy formation

• The cut-off is originate from structure formation process

46

0.0710

10Fe

solarcloud baryon

MZ Z

M

1st mini-halo ~ 106-7 M☉

SN

[Fe/H]~-4

After 1st SN explosion,

Pop.3 stars still alive HMP star. ⇒(Suda et al.2004)

MDF cut-off at [Fe/H]~-4

2nd star [Fe/H]~-4

merge

Merger tree

　 z

mini-haloの質量(M☉)

0.1 0.2 0.5 1 　　　 ( Big Bang からの時間 Gyr)

（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

Effect of structure formationEffect of structure formation

Merging history: Press-Schechter(Somerville & Kollat1999)

Model predict cut-off at [Fe/H]~-4.

SFE: 10-10/yr

Observed MDF

Theoretical MDF with merger tree.

Number of stars with Z = 0 is inconsistent.

Results

Assumptions

First starFirst 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

ContentsContents• Papers: Papers: 9696 (covering since 2000) (covering since 2000) on high resolution spectroscopy

• Stars: Stars: 1495(847)1495(847)• DataData

– [X/Fe]: [X/Fe]: 24,49824,498– [X/H]: [X/H]: 26,09026,090– loglogεε: : 26,09026,090– ＬＬ ogog g, etc; atmospheric data, g, etc; atmospheric data, 　　　　　　　　

[Fe/H] Number(prev.)[Fe/H] Number(prev.)

-1< -1< 124124 -1~-2 -1~-2 214214 -2~-3 -2~-3 419419 -3~-4 -3~-4 117117 <-4 <-4 44

[Fe/H] Number(prev.)[Fe/H] Number(prev.)

-1< -1< 124124 -1~-2 -1~-2 214214 -2~-3 -2~-3 419419 -3~-4 -3~-4 117117 <-4 <-4 44

(DaGaAr: Suda et al. 2007)

Sample characteristics

Magnitude distributionamong samplesselection effects due to survey

Teff - surface

gravity

dwarfs

giants

Metallicity distribution

[Eu/

Fe]

[Fe/H]

Eu: neutron capture element

r-process + s-process

r-process only[Eu/Ba] > 0

Space distributions of EMP stars

Distance ← surface gravity (assuming M=0.8 M)

dwarfs

giants

Astrometry ＋Spectroscopy (e.g., WFMOS ） ↓位置、運動、光度、組成 ⇒ 年齢

銀河の恒星地図銀河形成史の再構築