古い恒星系で探る天の川銀河の化学進化と元素の起源
Lamp spectra with Subaru/
Prime Focus Spectrograph(PFS) under construction

石垣美歩（国立天文台・ハワイ観測所）
天文・天体物理若手夏の学校、太陽・恒星セッション
２０２３年８月１−４日

https://pfs.ipmu.jp/blog/2021/10/p1924

東京大学本郷キャンパス

Credit: ESA/Gaia/DPAC, Acknowledgement: A. Moitinho.

Outstanding questions
What old stellar populations in the Milky Way tell us?

Where does the Solar-system came from?
26 Jul 2002

16:36

AR

AR166-AA40-13.tex

AR166-AA40-13.SGM

LaTeX2e(2002/01/18)
P1: IBD
10.1146/annurev.astro.40.060401.093840

How galaxies formed and evolved?
Annu. Rev. Astron. Astrophys. 2002. 40:487–537
doi: 10.1146/annurev.astro.40.060401.093840
c 2002 by Annual Reviews. All rights reserved
Copyright ∞The nature of dark matter

See Freeman & Bland-Hawthorn 2002

THE NEW GALAXY: Signatures of Its Formation

Beers & Christlieb05, Nomoto+13, Frebel & Norris15, Kobayashi+20

ed from www.annualreviews.org
of Japan on 07/31/23. For personal use only.

The origin of metals

Ken Freeman
Mount Stromlo Observatory, Australia National University, Weston Creek, ACT 2611,
Australia; email: kcf@mso.anu.edu.au

Joss Bland-Hawthorn
Anglo-Australian Observatory, 167 Vimiera Road, Eastwood, NSW 2122, Australia;
email: jbh@aao.gov.au

Key Words cosmology, local group, stellar populations, stellar kinematics■ Abstract The formation and evolution of galaxies is one of the great outstanding
problems of astrophysics. Within the broad context of hierachical structure formation,

Origin of metals in the Universe

detailed descriptions and references listed in Table 6.).

Solar system abundance
Lodders, K. 2020, Solar Elemental Abundances

H, He: 98.5 %Metals（金属）: 1.5 %(O: ~ 0.6 %, C: ~ 0.3%)

The chemical evolution of the Universe
Supernovae of
massive stars

Neutron star merger

Evolution of lowmass stars

Type Ia
supernovae

First (Pop III) stars

The Milky Way

0

Age of the Universe

13.8 Gyrs

NASA/WMAP science team

Old/metal-poor stars: fossil records of the synthesis of metals in the early Universe

Contents
How to nd “old” or metal-poor stars in the Milky Way?

- Wide- eld imaging and spectroscopic surveys
What metal-poor stars tell us?

- The origin of elements in the early Universe
Open questions about the origin of elementsfi

fi- Prospects with new instruments and telescopes

Contents
How to nd “old” or metal-poor stars in the Milky Way?

- Wide- eld imaging and spectroscopic surveys
What metal-poor stars tell us?

- The origin of elements in the early Universe
Open questions about the origin of elementsfi

fi- Prospects with new instruments and telescopes

Why “old” stars matter
Low-mass stars are long-lived:> 10 Gyrs for low-mass ( < 1M⊙) stars

Kinematics of stars are largely conserved: Inference on the initial orbit
The surface chemical composition is preserved during the main-sequencephase of stellar evolution: Chemical composition of the birth cloudfiExcellent probe of the star formation in the early Universe
e.g. the rst (Population III or Pop III) stars

Challenges in stellar age estimatesrgensen and L. Lindegren: Determination of stellar ages from isochrones
1.5much more complicated beelements in Z may vary (inther elements). These comscope of this paper and we

Jørgensen & Lindegren 2005

2.0

τ [Gyr] =
2.18

2.5

2.85

(2)

n for the present purpose ofdetermination by isochrones.
hat typical observational unof order ±0.1 dex, this relasolar metallicity, but should

MV [mag]

Distance uncertainty

129

3.27
3.82
3.0

3.5
ZAMS

rrors

purposes we usually assume
h are fairly representative ofwarfs in the solar neighbour1 dex in [Me/H], ±0.01 dex

Degeneracy/uncertainty instellar evolution models

4.0
3.85

3.80

log Teff [K]3.75

Color depends on chemical composition

Fig. 1. HR diagram showing the location of two hypothetical obser-

➡︎

The revolution of Galactic Archaeology with surveys
Parallax (distance)/proper motion: Gaia
Chemical abundance: LAMOST, GALAH, APOGEE, etc.
Asteroseismology: TESS, Kepler, K2

Gaia (ESA)

A&A proofs: manuscript no. 43511corr

a chronological table of the chemical enrichment history of our Galaxy

Chemical abundances of 5.5M stars
Gaia collaboration et al. 2022

Fig. 2. Sawith the mity [M/H]
tic plane,of the thintral Galact
mix of bul
is present.
metallicity
tances frommetal-poor

filter has a width of ∼100 A and covers the wavelength◦

Search for the most chemically pristine stars;
Narrow-bandsurveys
H&K
doublet lines (at 3968.5
and 3933.7 A), thereby al
A narrow-band lter covering Ca H+K lines
Pristine survey(Starkenburg+17)

Footprint
Sky Mapper
surveyFigureof
1. theSynthetic
spectra using
MARCS stellar atmospheres and the TURBOSPECTRUM code (see Section 2.1 for details) of stars on three different placeson the giant branch with metallicities [Fe/H] = 0.0 (red), [Fe/H] = −1.0
(orange), [Fe/H] = −2.0 (green), [Fe/H] = −3.0 (blue) and for a star withno metals (black). In the top panel the throughput of the Ca H&K filter usedin Pristine is overplotted (black dashed line).

fi

2011, and the dashed grey filter curve in Fig. 2). The SkyMapper
team has been using this filter to search for (extremely) metal-poorstars, their sample of candidates have already revealed some in-for a typical spread in radial velocity among the stars o
the Galactic halo, making it especially suited for our s
the remainder of the paper we will refer to this filter as
SMSS
0313-6708
filter, and to its measured magnitudes as CaHK magn
Sky Mapper survey (Keller+14)
comparison, we also show the SkyMapper v filter used f
purpose. Clearly, the CFHT CaHK filter is narrower andhat, resulting in a better sensitivity to the Ca H&K line s
less danger of leakage from other features such as strong
bands in C- and N-enhanced stars, as can be seen from thebetween the blue and black spectra in the figure.
The expected discriminative power of the CaHK filtedemonstrated in Fig. 3. The left-hand panel of this fi
the range of a spectral library in temperature and gravity
space and compares this with the stars as expected inhigh-latitude field in an anticentre direction as indica
Besançon model of the Galaxy (Robin et al. 2003). We ha library of synthetic spectra, illustrated here by the greylarge ranges in effective temperature, gravity and metall< [Fe/H] <+0.0) using Model Atmospheres in Radiativ
vective Scheme (MARCS) stellar atmospheres and the TURB
code (Alvarez & Plez 1998; Gustafsson et al. 2008; Plez
elements are treated as scaled from solar abundances, w
https://skymapper.anu.edu.au/data-release/#Coveragetion of the α-elements that are enhanced relative to scal
Copyright: ESA/Gaia/DPAC, CC BY-SA 3.0 IGO

The record holder of the lowest Fe abundnce:
SMSS 0313-6701 Galactic location and kinematics
Gaia

Steps in stellar chemical abundance analysis
Continuum, line strengths,
line shape…
Abundance[X/Y] = log(NX /NY) − log(NX /NY )⊙Atomic data
(excitation potential, partition
function, transition probability)

Physical properties of the star

Te , log g, [M/H] . . .

T(τ), P(τ), ρ(τ)…
τ: optical depthffstatic, plane parallel, local
thermo-dynamic equilibrium…

(Figure by Bengt Gustafsson,
Astronomical Observatory, Uppsala)

➡︎

➡︎

The chemical composition: Extremely Fe-poor and carbon enhanced
Keller+14[Fe/H] < − 6.53 (3σ)
Bessel+15, Nordlander+17−7

Ca abundance : 10of the Sun

Formed under extremely pristine
environment
4

C/Ca ratio >10 of the Sun
Unusual source of metals

A scenario for the metal-enrichment source
6

In a dark matter mini-halo ( ∼ 10 M⊙) at z ≳ 20

Metal yields of a Pop III star
experiencing large fallback leavinga ∼ 5 − 6M⊙ black hole.

Tominaga+07

Pristine (H) gas

Fe, metals
e.g., SMSS 0313-6708

A massive Pop III star 25 − 40M⊙

The rst metal-enriched stars:
Extremely metal-poor (EMP) ([Fe/H] < − 3 )Keller+14, Takahashi+14, Chan+17, Choplin+19, Chan+20

fi

Umeda&Nomoto05, Tominaga+07, MI, Tominaga, Kobayashi & Nomoto14

Credit: Kavli IPMU

The metallicity distribution function at lowest metallicities
A smoking gun of the nature of the rst stars and their metal enrichment process

Gray: Observation
Hartwig+22

rs (bottom
how other
2013; deal. 2018;
tom panel
Silk 2015;
ed lines in

Hunting of the lowest [Fe/H] will go on…

fie.g. ZERO survey (Subaru/HSC, PI: Chiba, M.)

Contents
How to nd “old” or metal-poor stars in the Milky Way?

- Wide- eld imaging and spectroscopic surveys
What metal-poor stars tell us?

- The origin of elements in the early Universe
Open questions about the origin of elementsfi

fi- Prospects with new instruments and telescopes

The origin of metals in the early Universe
Big Bang nucleosynthesis- Is the standard theory of BBN correct? Are the stellar evolution models correct?
The hydrostatic burning of massive stars, including the rst stars- Is the nature of the rst stars different from massive stars at present?
Core-collapse supernovae- How the massive stars explode? Were the explosion energy and/or geometry different?
Type Ia supernovae- How white dwarfs explode?
Neutron capture (s- or r-process) elementsfifi- Astrophysical sites of s- and r-processes in the early Universe?

AOKI ET AL.

Lithium and Big-Bangnucleosynthesis
Vol. 698

The Li resonance line in metal-poor stars
VH (km s−1 )c.86 −161.54 ± 0.09
.06 369.24 ± 0.30
.97 −281.67 ± 0.20
.94 −10.88 ± 0.16
.12 136.61 ± 0.13
.90 −49.43 ± 0.07
.98 −132.87 ± 0.27
.76 434.68 ± 0.03
.83
76.65 ± 0.06
.83 −14.63 ± 0.03
.00 −91.23 ± 0.03

y metal-poor stars,
the discrepancy
the prediction ofensity determined
the Li abundance
poor (EMP) stars,
326 (see also thesible connections
ll unknown, we

Production of Li in the Universe- Big Bang nucleosynthesis (BBN)- Cosmic-ray spallation- Stellar interiors- NovaFragile6
Destroyedat~10
K(e.g., Hydrogen burning ~ 107 K)
BBN (t ≲ 300s)

Aoki et al. 2009

Figure 1. Spectra around the Li i resonance line. The open circles show theThe predictions of the primordial Li abundance
and3

He/H = (1.00 ± 0.07) × 10−5

Cyburt+08

(7)

CMB

Predicted Li abundanceStandard BBN

SBBN+WMAP

Spite
Spite Plateau
PlateauAll
All stars
stars

2.5

Stars
Stars with
with T>5850–180[Fe/H]
T>5580–180[Fe/H]

0.5

HE 1327-2326
SM 0313–6708

SM 0313–
SM 0313–6708
6708(1) “Spite plateau”(Spite & Spite 1982)

cb S10+B12+G10
M10

Spite Plateau

SBBN+WMAP
Putative MS
SM 0313–6708

2.0
1.5
1.0

SD 1029+1728(2) Meltdown?

0.5

HE 1327-2326
SM 0313–
6708
6,500

Spite Plateau

6,000

Teff (K)c S10+B12+G10

All stars

Putativ
SM 031

1.5

Non-standard theories for the BBN?

b M10

SD 1029+
1728 SD 1029+1728
SM 0313–
0313–
SMHE 1327-2326
6708
6708

Aoki+09

5,500

2.0

Putative MS
SM 0313–6708

SBBN+WM

SDSD
1029+1728
SD 1029+1728Incomplete understanding
1029+1728
inLi
production/
1.0
SM 0313–
SM 031HE 1327-2326
HE
1327-2326
HE
1327-2326
6708
6708
destruction
in stars?
0.5
SM 0313–6708

All stars

2.5

A(Li)

Putative MS
SM 0313–6708+0.05

A( Li) = 2.72−0.06 (Cyburt et al. 2008)
SD 1029+1728

SBBN+WMAP

SBBN+WMAP
SBBN+WMAP

A(Li)BBN + CMB

7

1.0

3.0

3.0

.53:631-688. Downloaded from www.annualreviews.org. - National Observatory of Japan on 08/01/23. For personal use only.

A(Li)
A(Li)

2.0
1.5

SBBN+WMAPThe cosmological Li problem

2.5

A(Li)
A(Li)

Annu. Rev.
Astron. Astrophys.
2015.53:631-688. Downloaded from www.annualrevie
5.53:631-688.
Downloaded
from www.annualreviews.org
provided Observatory
by Kokuritsu-Tenmondai
Libr. - National
Observatoryof Japan on 08/01/23. For p.ss- Nationalof Japan on 08/01/23.
For personaluse only.

3.0

–6.0

3.0

SBBN+WMAP
SBBN+WMAP

2.5

Stars with T>5850–180[Fe/H]

2.0

Spite Plateau

Putative MS
SM 0313–6708

SBBN+WM
All stars

Putativ
SM 031

1.5
1.0
0.5

–4.0

[Fe/H]

Frebel&Norris+15

SM
SM 0313–
0313–
6708
6708

–6.0

SDSD
1029+1728
1029+1728
HE
HE 1327-2326
1327-2326
SM 0313–6708[Fe/H]c S10+B12+G10

SM 0316708–4.0

Measurement of Li abundances in the mostFigure3.0 6 SBBN+WMAP
3.0 SBBN+WMAP
Spite Plateau
SBBN+WMAP
SBBN+WMAP
Spite Plateau
SBBN+WM
metal-poor
is thekey!
A(Li) versus Teff (left) and [Fe/H] (middle and right) for near main-sequence stars having[Fe/H] < stars−2.0. The
circles
represent data
2.5

All stars

2.5

Stars with T>5850–180[Fe/H]

All stars

Synthesis of CNO in stars
Hydrogen burning through the CNO cycle- Main-sequence stars with ≳ 1M⊙
7- T ∼ 1.5 × 10 K

Bottle neck: most of the
12C are converted to 14N

Helium burning through the triple alpha process- The core of the red giant tip
8- T ∼ 1 × 10 K

Carbon burning- Massive stars
8- T ∼ 6 × 10 K

© 天文学辞典CNO enrichment in the early Universe
Core-collapse supernova

Credit: NASA

Asymptotic Giant Branch (AGB) stars

Winds from rotating massive stars

The origin of carbon-enhanced metal-poor (CEMP) stars

More metal-poor stars show higher [C/Fe]
ratios?

Possible explanation- Supernovae of the rst stars- Mass transfer from an AGB companion- Dust cooling in the formation of low-mass
second-generation stars- Rotating massive stars

fiSaccardi et al. 2023

Faint supernovae of the rst stars
AA53CH16-Frebel

ARI

29 July 2015

12:54

Ishigaki+14, Frebel & Norris 2015
Tominaga+07

6

SM 0313–6708
N

Astrophys. 2015.53:631-688. Downloaded from www.annualreviews.org
enmondai Libr. - National Observatory of Japan on 07/31/23. For personal use only.

EjectionC[X/Ca]O

HE 1327–2326
N

P

Cl

K

Sc

V

Mn

Co

Cu

Ne
F

Mg
Na

Si
Al

S
P

Ar
Cl

Ca
K

Ti
Sc

Cr
V

Fe
Mn

Ni
Co

Zn
Cu

0
C

O

HE 0107–5240
N

4

Ne
F

Mg
Na

Si
Al

S
P

Ar
Cl

Ca
K

Ti
Sc

Cr
V

Fe
Mn

Ni
Co

Zn
Cu

2
0
–2
6

C

O

Ne

Mg

Si

S

Ar

Ca

Ti

Cr

Fe

Ni

Zn

HE 0557–4840
N

4

F

Na

Al

P

Cl

K

Sc

V

Mn

Co

Cu

2
0
C

–2
2

O

Ne

SD 1029+1729
N

1

F

Mg
Na

Si
Al

S
P

Ar
Cl

Ca
K

Ti
Sc

Cr
V

Fe
Mn

Ni
Co

Zn
Cu

0
–1
–2

Umeda&Nomoto02, 03, Iwamoto+05, Tominaga+07, Ishigaki+14

Al

2

–2
6

[X/Ca]

Mixing zone

Na

0

4

[X/Ca]

Fallback

F

2

–2
6

[X/Ca]

The carbon enhancement as the resultof fallback of Fe or Ca to the compact
remnant[X/Ca]

4

C
5

O

Ne
10

Mg

Si

S
15

Ar

Ca
20

Ti

Cr

Fe
25

Ni

Zn
30

Atomic Number Z

fi

The origin of CEMP stars remain unclear… Larger samples
Figureof
12 elemental abundances in EMP stars are needed.

α-element: the most popular tracer of galactic chemical evolution
Massive stars with ∼ 10 − 100M⊙ → The core is hot enough to ignite carbon* α-element
9

Carbon and Neon burning（T ∼ 10[K], t ∼ 600 [yr]）→ Na、Mg、Ne、O

1
Oxygen burning（T ∼ 2 × 10 [K], t ∼
[yr]）
2
9

→ Si、S

Silicon burning（T ≥ 3 × 10

9[K], t ∼ 1 [day]）→ Fe、Ni (F-peak elements)

Abundance of nuclei determined by the temperature and density (thermal equilibrium)→ Onion-skin-like structure with an iron core

➡︎

➡︎

The fate of massive stars
9

Extremely high temperature and density（T ∼ 8 × 10

13[K], ρ ∼ 10

−3

[kg m ]）

Binding energy per nuclei

Presence of high-energy photon→ Photo-dissociation of Fe (endothermic)
An electron and a proton to produce neutrons→ Lose electron degenerate pressure
Eb = Δmc 2 = [Zmp + (A − Z)mn − mnucleus] c 2

Losing pressure support leads to Fe core-collapse
Core-collapse supernova → supernova nucleosynthesis

Explosive nucleosynthesis in core-collapse supernovae (CCSNe)
More elements are created at the time of explosion
Normal energy

E51 = E/1051[erg]Ishigaki et al. 2014

Explosive C burning: Ne, Mg
Explosive Ne burning: O, Si
Incomplete Si burning: Cr, Mn
High energy

Complete Si burning: Fe, Ni, Co, Zn

Nucleosynthesis products
depends on- Explosion energy- Mass cut

Chemical abundances of EMP stars as a tracer of Pop III CCSN yields
Ishigaki+18

15M⊙

E51 = 1040M⊙

E51 = 30

Extremely metal-poor (EMP) stars: The
chemical abundance pattern re ects a single
or a few Pop III CCSN yields
The α-element abundances in particulardepend on the progenitor masses
The initial mass function (IMF) of the Pop III
stars

100M⊙

fl

Progenitor mass

E51 = 1

Explosion energy

25M⊙A possible chemical signature of an extremely massive Pop III star
Xing+23, Nature
Credit: LAMOSTHigh Si/Mg

Credit: NAOJ

A new evidence of the presence of extremely massive ( > 100M⊙) Pop III stars as a source of metals in the early Universe

Type Ia supernovae: the production of Fe-peak elements
A thermonuclear explosion of a C-O white dwarf with M ∼ MCh

A white dwarf accreting mass from thecompanion

Products- Fe-peak elements (Mn, Fe, Ni)

Nucleosynthesis yields depend on
Merger of two white dwarfs- Central density of the white dwarf~107-109 g/cm3- Initial chemical composition

Present-day probes of the chemical evolution of the Universe
Solar system material, Solar photosphere, galaxy clusters
Tsujimoto+95, Mernier+18, Simionescu+19

Metal abundances in the Perseus galaxy
cluster by Hitomi satellite

Selecting nearby old stars by kinematics + elemental abundances + ages
MSTO stars with age > 12 Gyrs (×)
from Value-added catalog of
GALAH DR3 ( ∼ 600,000 stars)( Sharma+18; Buder+20; see also
Sanders&Das18)

Old Halo Stars (OHS)Isochrones of 10 Gyrs
Solar-α、α-enhanced
Stars with halo-likekinematics( | v − v⊙ | > 150km/s) from GALAHxGaia
EDR3“Old Halo Stars” : candidate of stars belonging to the old stellar
population in the Solar neighborhood (e.g., Di Matteo+19,
Gallart+19)

[X/Fe]-[Fe/H] subgroups
Metal-poor

High-αLow-αe.g., Nissen&Schuster10, Hawkins+15, Hayes+18,
Helmi+18, Belokurov+18, Koppelman+18, Simpson+20• High-α: rotation along the
disk• Low-α: high-eccentricity,
Gaia-Sausage-Enceladus• Metal-poor: small LZ(zero net rotation)

Constraints on the contribution of SN Ia to the metals in old halo stars
The relative fraction of SNIa of 5-10% best explain
the abundances in old halo stars
Metal-poor

Ishigaki+21

High-αAbout 20-40% of the mass of Fe
from SNIa in the early Universe

Mass fraction of Fe from Type Ia: 42%

Low-α

Posterior fIa

44%

Posterior fIa

19%

Mean of the posterior distribution of fIa

Chemical evolution models with all the possible channels

Kobayashi et al. 2020

Contents
How to nd “old” or metal-poor stars in the Milky Way?

- Wide- eld imaging and spectroscopic surveys
What metal-poor stars tell us?

- The origin of elements in the early Universe
Open questions about the origin of elementsfi

fi- Prospects with new instruments and telescopes

Summary of the open questions in the next decade
The nature of the very rst (PopIII) stars in the Universe- Diversity in chemical abundances in the outer Milky Way halo
- Consistency with the high-z observations (e.g. JWST)Supernova explosion mechanisms- Elements produced by explosive nucleosynthesis
The complete explanation of the Solar-system abundancesfi- Chemical evolution and the formation of the Milky Way

Recent and future multi-element surveys of Galactic stellar
populations
Majewski et al.
Majewski et al. 2017

Nelem =21

Nelem = 13

Nelem =24

PFS-MR

Nelem > 6

= λ/Δλ
Probing multiple nucleosynthesis channels: core-collapse SNe, SNIa, s/r/i process, etc.

Covering large volumes
Hayden et al. 2015

Sun

Majewski et al 2017

APOGEE plate (~ 300 stars)
Majewski+15

Solar neighborhood

Multi-element abundances: probe of multiple nucleosynthesis channels
Elemental abundance distribution from GALAH survey

Buder et al. 2021
Big bang
nucleosynthesis

Core-collapse
supernovae

Neutron star merger

Type Ia supernovae

Asymptotic Giant
Branch stars

41• Prime Focus Spectrograph (PFS)/Subaru• Wide eld (1.3deg^2), >２３００ bers
• Identi cation of chemically pristine stars in thedwarf satellite galaxies and eld halo stars.

The prime focus• HROS/TMT• Detailed elemental abundance estimates of themost metal-poor stars• Test theories of supernova/stellar nucleosynthesis
Nature of the rst stars and their metal yields

fi

fi

fi

fi

fi

fi

2394 bers in the eld-of-viewfi➡︎The next generation instruments

PFS: wide- eld and deep spectroscopic surveys ofthe dwarf satellites
Sculpter dwarf satellite Walker et al. 2009, AJ, 137, 3100; Walker et al. 2009, ApJS, 171, 389

Field of views of PFS

V mag

Apparent magnitude

Previous surveys

Previous instruments

PFS/Subaru

fi

Color

Ultra-faint dwarf galaxies: A large fraction of CEMP and r-rich stars
Best suited to constrain the astrophysical sources responsible for producing the metals
Frebel et al. 2014
Segue I8-10m telescopes

TMT

Credit: Kavli IPMU

The nature of the rst
stars
fi

➡︎

TMT：High-resolution spectroscopy of stars in ultra-faint dwarf

Summary
How to nd “old” or metal-poor stars in the Milky Way?

- Wide- eld imaging and spectroscopic surveys have been successful in nding chemically pristine stars and constraining their metallicity
distribution function (MDF).

- The MDF at the lowest [Fe/H] range is important, but missing.
What metal-poor stars tell us?

- The origin of elements in the early Universe have been constrained by chemical abundance patterns in metal-poor stars.
- The primordial abundance and BBN- The nature and explosion mechanisms of the Pop III stars- Progenitors of SNIa
Open questions about the origin of elements- Prospects with new instruments and telescopes: a larger volume including the Milky Way outer halo and more detailed elemental

fi

fi

fi

abundances to constrain supernova yields in the early Universe.