# Presentation: 394452

## Understanding the Characteristics of EMP stars as Probes for the Early Universe - Stellar Evolution of Low- and Intermediate-Mass EMP Stars

- _Takuma Suda__1_,
- &
- Masayuki Y. Fujimoto1

** ****First Stars III, La Fonda Hotel, Santa Fe, Jul. 17, 2007**

- 1 : Hokkaido University

## Number of Observed EMP stars

- Beers & Christlieb ARAAP 2005

- Searches for metal-poor stars in the Galactic halo since 1980s
- Many stars with [Fe/H] ~ -3, but 2 stars below [Fe/H]=-5

- EMP : Extremely Metal-Poor

**■****HK**
**■****HAMBURG/ESO**

**From the database of metal-poor stars by T.S. et al. (in prep.)**

## Large fraction of carbon rich stars ([C/Fe] >~ 0.5) (CEMP stars) compared with the Population I & II stars 
Two groups of CEMP stars : with/without enhancement of s-process elements (CEMP-s and CEMP-no(s), respectively)

- Large fraction of carbon rich stars ([C/Fe] >~ 0.5) (CEMP stars) compared with the Population I & II stars
- Two groups of CEMP stars : with/without enhancement of s-process elements (CEMP-s and CEMP-no(s), respectively)

**Characteristics of EMP Stars**

- [Fe/H]

- [C/Fe]

- [C/Fe]

- [Ba/Fe]

**T.S. et al. (in prep.)**

**“****C-rich” for [C/Fe] > 0.5**
**“****EMP” for [Fe/H] < -2.5**
**“****Giants” for Teff < 6000K and log g < 3.5**

**CEMP-s**

**CEMP-no**

## Motivations

- Low- and Intermediate- mass models with [Fe/H] < -2.5 can be responsible for CEMP stars.
- Previous works by Fujimoto et al. (1990), Hollowell et al. (1990), Fujimoto et al. (2000), Schlattl et al. (2001), Picardi et al. (2004)
- What is the fate of EMP models under the standard stellar evolution theory?
- Is it possible to reproduce observed characteristics of EMP stars assuming binarity?
- Explanation for CEMP-s and CEMP-no

## Models of Stellar Evolution

- One-dimensional adaptive mesh
- Thermal convection by Schwartzschild Criterion
- Mixing parameter α=1.5
- No overshoot and No semi-convection
- Most up-to-date input physics
- 9 elements with reaction rate : NACRE
- radiative and conductive opacities : OPAL, Alexander & Ferguson (1994), Itoh et al. (1983)
- neutrino cooling processes : Itoh et al. (1996)
- No inclusion of mass loss and extra mixing
- Simple assumption for He-FDDM

**see T.S., Fujimoto, Itoh (2007, ApJ in press)**

## Evolution of EMP models

- 1.0

- 1.5

- 2.0

- 8.0

- 1.0

- 1.5

- 2.0

- 8.0

- 0.8M⦿

- 0.8M⦿

**log L vs. log T****eff**

**log T****c**** vs. log ****ρ****c**

- Core
- He-flash

**[Fe/H]=-3**

## He-FDDM in EMP

**He-FDDM in EMP**

**Helium shell flash phase**

**Time**

**M****r**** : mass coordinate**

- He/H
- interface

- Surface
- convection

**He-Flash**
**Convection**

- He-FDDM

- 3rd dredge-up

**H-Flash**
**Convection**

- With/Without splitting the convection

**12C(p,****γ****)13N(e+****ν****)13C(****α****,****n****)16O**
**& **_**Neutron Capture Nucleosynthesis**_

**T.S. et al. (2004), Komiya et al. (2007)**

## Thermal Pulses on AGB and He-FDDM

**Thermal Pulses on AGB and He-FDDM**

**1.2M****⦿****, [Fe/H]=-3**

**0.4Myr**

**C**

**N**

**O**

**Mixed protons are used to operate CN cycle.**

**Dredge-up after Mixing**

**0.27Myr**

**Proton Mixing**

**X : Mass Fraction**

## Thermal Pulses on AGB and He-FDDM

**Thermal Pulses on AGB and He-FDDM**

**3M****⦿****, [Fe/H]=-4**

**C**

**N**

**O**

**Mixed protons are used to operate CN cycle.**

**Third drege-up**

**X : Mass Fraction**

## Classification by Surface Abundances

- (Fujimoto et al. 2000,
-  T.S & Fujimoto 2007, in preparation)

**Classification by Surface Abundances**

**Initial Mass (M****⦿****)**

**0.8     1.0  1.1 1.2 1.5     2.0   2.5    3.0           4.0            5.0           6.0           7.0         8.0         9.0**

**[Fe/H]**

- Weak TDU

- Strong TDU

## Summary

- EMP models are computed.
- Z=0, -5<[Fe/H]<-2.3
- 0.8 < M/M⦿ < 9.0
- There are 2 channels for He-flash driven deep mixing during AGB phase.
- Violent proton mixing and strong dredge-up
- Weak proton mixing and long duration of nucleosynthesis
- Strength of the 3rd dredge-up have variations for mixing length of 1.5.
- Strong/Weak/No TDU for M>~1.5M⦿
- Candidate for CEMP-s and CEMP-no

**ADVERTISEMENT for International Conference**
**“****Origin of Matter and Evolution of Galaxies 2007(OMEG07)”**
**Dec. 4-6, 2007, Hokkaido University**