THE FIRST STARS: THE FIRST STARS:

Uranium-rich metal-poor starUranium-rich metal-poor star

CS 31082-001CS 31082-001

HST – STIS 45 orbits – 43 completedHST – STIS 45 orbits – 43 completed PI: Roger Cayrel (2001 – 2004)PI: Roger Cayrel (2001 – 2004) Useful range: 250-310nm, R~30,000Useful range: 250-310nm, R~30,000

B. Barbuy, M. Spite, V. Hill, F. Primas, B. Plez, B. Barbuy, M. Spite, V. Hill, F. Primas, B. Plez, C. Sneden, F. Spite, T.C. Beers, J. Andersen, C. Sneden, F. Spite, T.C. Beers, J. Andersen, B.Nordstrom, P. Bonifacio, P. François, P. B.Nordstrom, P. Bonifacio, P. François, P. Molaro, C. Siqueira-MelloMolaro, C. Siqueira-Mello

Evolution of Universe vs. redshift

The first generation of stars was never observed but should be detected in 2 ways:

-High mass stars explode as supernovae and produce a GRBs (z ~ 15 ?) GRB at z~8.2 = pop. III?

-First generations of low mass stars should be still evolving, identified by a very low metallicity (or no metals) (z ~ 5 to 15)

Cayrel etal. 2001,Nature

First Detection of Uranium in an old star

CS31082-00114 +-3 Gyr

Now: 3 suchstars detected

Neutron-capture elements are formed through the s- and r-processes.For example, in the solar system: Barium = 15% r + 85% s Europium = 97.3% r + 2.7% s

In metal-poor stars, however, only the r-fraction produced in the first SNae is present.

r-process site(s): not yet confirmed

Beers & Christlieb 2005, ARA&A

So far, 12 r-II stars (Hayek et al. 2009)

6 with well-detected Thorium

3 (2) stars with Uranium detected:

● CS 31082-001 (Cayrel et al. 2001; Hill et al. 2002)● HE 1523-0901 (Frebel et al. 2007)● BD+17º3248 (Cowan et al. 2002)

USE OF STIS SPECTRUM IN ORDER TO:

●Measurements of new elements, in parti- cular the heaviest elements near the actinides U, Th: Bi, and Pb, produced in the same r-process event better age derivation

●Other dominantly r-elements: Eu, Os, Ir

● New elements in the other r-process peaks

LOG A(X) Z Sun VLT HST [X/Fe]Os 76 1.40 0.43 0.43 +1.30Ir 77 1.38 0.20 0.20 +1.75 Pt 78 1.62 ---- 0.65 +1.93 Au 79 1.01 ---- -0.40 +1.58Pb 82 1.75 -0.55 -0.65 +0.50Bi 83 0.71 ---- -0.50 +1.54Th 90 0.06 -0.98 ------ +1.86U 92 -0.54 -1.92 ------ +1.52

3rd peak elements and actinides

There are 3 types of chronometers involving U, Th radioactive elements(Cayrel et al. 2001, Nature, 409, 691):

Using different production ratios (PRs)

U/Th gives ages of 13.9 to 15.7 Gyr

PRs for U/Os, U/Ir, U/Pt, U/Au, U/Bi more uncertain

AGES (Gyr)U/Os 11.5 Schatz02U/Ir 11.7 Wanajo02U/Pt 11.8 Wanajo02U/Au 9.7 Wanajo07aU/Bi 13.8 Wanajo07bU/Th 13.95 Goriely01 U/Pb 11.8 Wanajo07b

Roederer et al. 2009 : universality of abundance pattern of heavy r-process elements applies to Ba to Pt.

It seems not to extend to Pb and beyond.

4 stars were found to show actinides boost:CS30306-132, [Fe/H]=-2.97 (Honda)CS31078-018, [Fe/H]=-2.85 (Lai)HE1219-018, [Fe/H]=-2.42 (Jonsell)CS31082-001, [Fe/H]=-2.9 (Hill) so far this is not understood

Conclusions:● First measurement of Bi, Au● Lowest metallicity oldest stars = laboratories for insights into the r-process nucleosynthesis● STIS UV spectrum: legacy for atomic physics in terms of lines of heavy elements and FeII● Independent constraint on the age of the oldest stars

SCIENCE:

r-process site identification and calculations of r-elements production:

Among the 11 greatest unanswered Questions in Physics

NEXT STEPS:

For a better understanding of the r-process:1st peak: 38Sr, 39Y, 40Zr, 41Nb, 42Mo 44Ru, 45Rh, 46Pd, 47Ag, 48Cd

Electron-capture supernovae (ECSNe), with O-Ne-Mg cores of small mass (~1.38M☺ ) high Sr-Y-Zr, Zn low heaviesorHigh mass stars with rotation (Geneva)

2nd peak would complete the r-process scenario:

Ba, La, Ce, Pr, Nd, Sm, EU => optical

In the STIS region: a wealth of lines of:

Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu

The End