# Presentation: 279045

## An Observational Perspective on Some Aspects of Early Stellar Nucleosynthesis 

- Chris Sneden
- University of Texas at Austin

## My own work is a product of the collective efforts of many people, including:

- John Cowan
- Jim Truran
- Scott Burles
- Tim Beers
- Jim Lawler
- Inese Ivans
- Jennifer Simmerer
- Caty Pilachowski
- Jennifer Sobeck
- Betsy den Hartog
- Scott Burles
- George Fuller
- Anna Frebel
- Bob Kraft

- Jennifer Johnson
- George Preston
- Debra Burris
- Bernd Pfeiffer
- Karl-Ludwig Kratz
- Francesca Primas
- Sara Lucatello
- Taft Armandroff
- Andy McWilliam
- Roberto Gallino
- Bob Kraft
- Vanessa Hill
- Ian Roederer
- Christian Johnson

## Outline, of sorts

-   can’t cover all topics
-   trying to give a flavor of progress
-   (of course) some obervational hand-wringing
-   others will have to talk of premodial nucleosynthesis (He, Li, Be, B)
-   concentrating here on:
-   “alpha” elements (Mg, Si, Ca, Ti easily done)
-   “neutron-capture” elements
- r-process-rich
-  s-process-, carbon-rich

## Bernard E. J. Pagel (1930-2007)

- Bernard Pagel and Margaret Burbidge at a 2003 meeting
- Don Clayton photo: http://www.astro.clemson.edu/NucleoArchive/

- Pioneer in abundances, HII regions, nucleosynthesis, chemical evolution of galaxies
- University of Sussex, NORDITA

## Let’s start on a good note:  spectroscopy yields the solar system composition very well

- Sneden & Lawler 2005

##  element overabundances: First Stars survey

-  element overabundances: First Stars survey

- Cayrel et al. 2004

##  element overabundances: First Stars survey

-  element overabundances: First Stars survey

- Cayrel et al. 2004

## Scatter in the  elements

- Scatter in the  elements

- Giridhar et al. 2001

## Alpha-rich, alpha-poor

## Alpha-rich, alpha-poor: comparison to HD 122563

## Exotic mass ranges of progenitor stars need to be invoked ...

- Aoki et al. 2007

## Wait:  some observational difficulties

- Preston et al. 2006

## Plotting versus temperature reveals the problem

- Preston et al. 2006

## Not a problem exclusive to one survey

- Preston et al. 2006

## Be cautious with abundances derived from 1-2 very strong lines (and above ground state)

- And Si is substantially ionized

## Major work still to be done on transition probabilities of alpha elements

## s-process: β-decays occur between successive n-captures
r-process: rapid, short-lived neutron blast 
           temporarily overwhelms β-decay rates
r- or s-process element: origin in solar-system 
           dominated by one or the other process

*s*-process: β-decays occur between successive n-captures
*r*-process: rapid, short-lived neutron blast
-            temporarily overwhelms β-decay rates
*r*- or *s*-process element: origin in ***solar-system***
-            dominated by one or the other process

- Rolfs & Rodney (1988)

- Neutron-capture elements

## A close look at the neutron-capture synthesis paths: different isotopes are made in r- and s-processes

- Ba

- La

- Cs

- Xe

- 139

- 132

- 131

- 130

- 129

- 128

- 130

- 132

- 133

- 134

- 136

- 134

- 135

- 136

- 137

- 138

- 138

- p

- p

- s,r

- s,r

- s,r

- s,r

- s,r

- s,r

- s

- r

- s,r

- r

- p

- s

- s,r

- s

- s

*r*-process path

*s*-process path

## Today we know of lots of “r-process” stars, such as CS 22892-052

- Note the trend

- Sneden et al. 2003

## “pure” r-process stars: good match to solar r-only

- “pure” r-process stars: good match to solar r-only

- Ivans et al. 2006

## “one” answer Z=56-82, not so for lighter elements

- “one” answer Z=56-82, not so for lighter elements

- Ivans et al. 2006

## The de-coupling of the heavy/light r-process (?)

- Johnson & Bolte 2002

- See also Aoki 2005, and their new astroph posting

## Now TWO solid uranium detections

- Frebel et al. 2007

## And several ways to estimate ages

- Frebel et al. 2007

## Credit where it belongs:  laboratory progress on n-capture (Z>30) element transitions

**Rb**

**Sr**

**Y**

**Zr**

**Nb**

**Mo**

**Tc**

**Ru**

**Rh**

**Pd**

**Ag**

**Cd**

**In**

_**Sn**_

**Sb**

**Te**

**I**

**Sc**

**Ca**

**K**

**Xe**

**Ti**

**V**

**Cr**

**Mn**

**Fe**

**Co**

**Ni**

**Cu**

**Zn**

_**Ga**_

_**Ge**_

**As**

**Se**

**Br**

**Kr**

**Be**

**Li**

**Mg**

**Na**

_**Hf**_

_**Ta**_

_**W**_

**Re**

_**Os**_

_**Ir**_

_**Pt**_

_**Au**_

**Hg**

**Tl**

_**Pb**_

_**Bi**_

**Po**

**At**

**Rn**

**Ra**

**Fr**

**Ba**

**Cs**

**Rf**

**Db**

**Sg**

**Bh**

**Hs**

**Mt**

**Uun**

**Uuu**

**Uub**

**C**

**B**

**O**

**F**

**Ne**

**Ar**

**Al**

**Si**

**P**

**S**

**Cl**

**N**

**He**

_**La**_

_**Ce**_

_**Pr**_

_**Nd**_

**Pm**

_**Sm**_

_**Eu**_

_**Gd**_

_**Tb**_

_**Dy**_

_**Ho**_

_**Er**_

_**Tm**_

_**Yb**_

_**Lu**_

**Ac**

_**Th**_

**Pa**

_**U**_

**Np**

**Pu**

**Am**

**Cm**

**Bk**

**Cf**

**Es**

**Fm**

**Md**

**No**

**Lr**

**In**

**Sb**

**Te**

**I**

**Xe**

**Po**

**At**

**Rn**

- lighter element

**H**

- n-capture, unobservable

- n-capture, atomic data OK?

- n-capture, recent lab transitions

- Three groups contribute especially: Lund, Liege, Wisconsin

## Atomic structures of rare earth ions are happier

## One example of a key element: hafnium

- Ivans et al. 2006

- Hf

- Hf

- Th

- Th

## VERY few accessible Hf II lines

- Ivans et al. 2006

## Why Hf matters: begin with estimates of neutron density ranges for the r-process

- Kratz et al. 2007

## This leads to relatively constant Hf/Th production in the r-process

## And observed Hf abundances correlate well with Eu (and La)

- And _*observed*_ Hf abundances correlate well with Eu (and La)

- Lawler et al. 2007

## Where are they in the HR diagram?

- Lack of many unevolved r-process stars is a problem of line strengths?

## The Hamburg-ESO (HES) r-process survey 

- Barklem et al. 2005

- Here are the statistical distributions

-  253-star “snapshot” detailed survey (R ~ 20,000, S/N ~ 50)
-  small number of n-capture elements; approximate abundances
-  stars with very strong CH bands discarded from sample (for now)
-  8 new stars with [Eu/Fe]>+1.0 and 35 more with [Eu/Fe]>+0.3

## HES: mostly “r-rich” stars, with a few “s” ones

- Solar r+s

- r-only

- s-only

- Barklem et al. 2005; dashed lines are scaled solar-system s-only abundances

## Galactic halo metal-poor stars are often carbon-rich

- Rossi et al. 2005

## C-rich stars are often Pb-rich at lower metallicities

- Van Eck et al. 2003

## The “blue-metal-poor” C-rich stars are simpler to analyze

- Ivans et al. 2005

## Where are they in the HR diagram?

- Like globular cluster blue stragglers

## What about C-rich stars that are NOT s-process-enhanced?

- careful! NOT statistically unbiased samples

## An example of a detailed abundance pattern for an s-rich star: must have prior (?) r-process?

- Ivans et al. 2005

## progress hampered by lack of lines of critical elements

## But early appearance of vigorous r- and s-process leads naturally to scatter in La/Eu trend with [Fe/H]

- The La/Eu (e.g, the *s-/r-*) ratio is NOT a simple function of [Fe/H]

- Simmerer *et al.* (2004)

- Basic trend: more
- s-process at higher [Fe/H], but the detailed situation is complex

## This is just to introduce some of the topics

-   Several focused talks tomorrow
-   Please look at the posters for this meeting!
-   We need to critically examine the Fe-peak elements (Z=21 to 30)
-   Support your local laboratory spectroscopist!
-   We cannot ask theoreticians to correctly interpret observations that we cannot guarantee