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THE FIRST STARS:
Uranium-rich metal-poor star
CS 31082-001
– STIS 45 orbits – 43 completed
 PI: Roger Cayrel (2001 – 2004)
 Useful range: 250-310nm, R~30,000
 HST
 B.
Barbuy, M. Spite, V. Hill, F. Primas, B.
Plez, C. Sneden, F. Spite, T.C. Beers, J.
Andersen, B.Nordstrom, P. Bonifacio, P.
François, P. Molaro, 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)
First Detection of Uranium in an old star
Cayrel et
al. 2001,
Nature
CS31082-001
14 +-3 Gyr
Now: 3 such
stars 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 particular 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
3rd peak elements and actinides
Os
Ir
Pt
Au
Pb
Bi
Th
U
Z Sun
76 1.40
77 1.38
78 1.62
79 1.01
82 1.75
83
0.71
90
0.06
92 -0.54
LOG A(X)
VLT HST [X/Fe]
0.43 0.43 +1.30
0.20 0.20 +1.75
---- 0.65 +1.93
---- -0.40 +1.58
-0.55 -0.65 +0.50
---- -0.50 +1.54
-0.98 ------ +1.86
-1.92 ------ +1.52
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
U/Os
U/Ir
U/Pt
U/Au
U/Bi
U/Th
AGES (Gyr)
11.5 Schatz02
11.7 Wanajo02
11.8 Wanajo02
9.7 Wanajo07a
13.8 Wanajo07b
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 heavies
or
High 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