Transcript Early Galactic Nucleosynthesis: The Impact of HST/STIS

Early Galactic Nucleosynthesis: The Impact of
HST/STIS Spectra of Metal-Poor Stars
Chris Sneden
University of Texas
A Very Collaborative Effort
•
•
•
•
•
•
•
•
•
•
John Cowan
Jim Truran
Scott Burles
Tim Beers
Jim Lawler
Inese Ivans
Jennifer Simmerer
Caty Pilachowski
Jennifer Sobeck
Betsy den Hartog
•
•
•
•
•
•
•
•
•
•
David Lai
Scott Burles
George Fuller
Anna Frebel
Bob Kraft
Angela Bragaglia
Norbert Christlieb
Beatriz Barbuy
Anna Marino
Raffaele Gratton
•
•
•
•
•
•
•
•
•
•
Jennifer Johnson
George Preston
Debra Burris
Bernd Pfeiffer
Eugenio Carretta
Jackson Doll
Karl-Ludwig Kratz
Francesca Primas
Sara Lucatello
Taft Armandroff
•
•
•
•
•
•
•
•
•
•
Andy McWilliam
Roberto Gallino
Evan Kirby
Vanessa Hill
Ian Roederer
Christian Johnson
Sloane Simmons
Valentina D’Orazi
Ian Thompson
Matt Alvarez
Definitions:
[A/B] = log10(NA/NB)star – log10(NA/NB)Sun
log ε(A) = log10(NA/NH) + 12.0 (spectroscopic)
log N(A) = log10(NA/NSi) + 6.0 (meteoritic)
today two topics:
- the neutron-capture elements
- return to the Fe-peak
the common thread:
nucleosynthesis at the end of stellar lives
HST/STIS spectra: relevant to entire nuclide range
Heaviest stable elements
a.k.a 3rd neutron-capture peak
Understudied lighter neutron-capture elements
Fe-group elements
Light elements (Be, B)
http://atom.kaeri.re.kr/
The ultimate question? How did our Galaxy
produce the solar chemical composition?
SCG08 = Sneden, Cowan, & Gallino 2008, ARA&A, 46, 241
First discussion: n(eutron)-capture elements
Most isotopes of elements with Z>30 are formed by:
AZ + n
A+1Z
Followed by, for unstable nuclei:
A+1Z
A+1(Z+1) + b-
H
Li
He
Be
B
C
N
O
F
Ne
Na Mg
Al
Si
P
S
Cl
Ar
Cu Zn Ga Ge As
Se
Br
Kr
I
Xe
K
Ca
Sc
Ti
Rb
Sr
Y
Zr Nb Mo Tc
Cs
Ba
Hf
Fr
Ra
Rf Db Sg Bh Hs Mt Uun Uuu Uub
La
V
Ta
Ce
Cr Mn Fe Co
W
Ni
Ru Rh Pd Ag Cd
Re Os
Ir
Pt Au Hg
In
Sn Sb
Te
Tl
Pb
Po
Bi
At Rn
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
Buildup of
n-capture
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
Rolfs & Rodney (1988)
A detailed look at the r- and s-process paths
“s-process”
element
“r-process”
element
SCG08
n-capture spectra of metal-poor stars
HD 122563:
[Fe/H] = -2.7
Teff ~ 4750
LOW n-capture
CS 22892-052:
[Fe/H] = -3.1
Teff ~ 4750
HIGH n-capture
“r-process-rich” metal-poor stars
An important abundance
ratio:
log e(La/Eu) = +0.6
(solar total)
= +0.2
(solar r-only)
= +1.5
(solar s-only)
first example, HD 115444, was reported by Griffin et al. 1982
SCG08
Lawler et al. 2009
Sneden et al. 2009
Sneden et al. 2009
Sneden et al. 2009
Lawler et al. 2007
Ba La
Ce
Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb
Lu
Hf
14 45
4
5
46
15 32 15 37
55
36 14
9
20
32
2
7
13
Sun: # transitions used in analysis
8
3
1
29 13 21
6
1
3
CS 22892-052 : # transitions used in analysis
Sneden et al. 2009
Lawler et al. 2008
Lawler et al. 2004
Sneden et al. 2009
Lawler et al. 2000b
Den Hartog et al. 2003
Lawler et al. 2001
Lawler et al. 2006
(unstable element)
Den Hartog et al. 2003
Lawler et al. 2000a
(well studied in literature)
why are rare earths well understood?
Wisconsin lab studies: log gf and hyperfine/isotopic structure
1
4
8
n-capture compositions of wellstudied r-rich stars: Così fan tutte??
lines are solar-system
abundances
differences from
solar-system
means of the
differences
SCG08
Thorium/Uranium detections
promise alternate Galactic ages
Frebel et al. 2007
leading to possible radioactive decay ages
Persistent question:
why is Pb usually low?
U/Th ratio should
be best age
indicator, if both
elements can be
detected reliably
Frebel et al. 2007
good abundances really confront r-process predictions
Ivans et al. 2006
But! crucial element groups for further progress
Ivans et al. 2006
Beyond simplest results: de-coupling of the
heavy/light r-process elements
ZY = 39
ZBa = 56
See also Aoki et al. 2005, 2007
Johnson & Bolte 2002
r-process abundance distribution variations: "normal"
Roederer et al 2010
But various densities must contribute to r-process
decreasing density components
increasing density components
Kratz et al. 2007
Niobium (Nb, Z=41):
surrogate for
remaining n-capture
elements (and their
“issues”)
these are the best
transitions in the
most favorable
detection cases
Nilsson et al. 2010
Niobium: here is why
there are difficulties
All reasonably
strong lines are in
the vacuum UV;
this is why STIS is
good here
Nilsson et al. 2010
UV spectra of 3 metal-poor giants
HD 122563:
[Fe/H] = -2.7
Teff ~ 4750
LOW n-capture
HD 115444:
[Fe/H] = -2.9
Teff ~ 4650
HIGH n-capture
BD+17 3248
[Fe/H] = -2.2
Teff ~ 5200
HIGH n-capture
Roederer et al 2010
Initial STIS exploration
HD 122563:
[Fe/H] = -2.7
Teff ~ 4750
LOW n-capture
HD 115444:
[Fe/H] = -2.9
Teff ~ 4650
HIGH n-capture
CS 22892-052
[Fe/H] = -3.1
Teff ~ 4750
HIGH n-capture
Cowan et al. 2005
Heaviest stable
elements scale
with Eu
Again, Eu is the usual
“pure” r-process element
Cowan et al. 2005
But light n-capture
elements do NOT
scale with Eu
Cowan et al. 2005
Upon further review of these same STIS data …
Points = data
Lines = syntheses:
•
best fit (color)
•
± 0.3dex
(dotted)
•
no element (solid)
Roederer et al 2010
Helps “complete” the n-capture distribution
Points = observations
Blue line = SN ν wind
Farouqi et al. 2009
Gray lines = scaled
solar-system
Roederer et al 2010
Second discussion:
back to the Fe-peak
McWilliam 1997
sharpening & extension by “First Stars” group
Cayrel et al. 2004
elements that
can be directly
predicted in SNe
models
crucial distinction from
n-capture elements:
the Fe-peak element
productions can
actually be predicted
theoretically
Kobayashi et al. 2006 (following Timmes et al. 1995)
for some
elements, all
seems well
Kobayashi et al. 2006
(solid line new results
but for others,
discomfort
neutral lines
same predicted Cr abundances
ionized lines
Kobayashi et al. 2006
should be simple to do Fe-peak elements:
their abundances >> n-capture ones
r-process-rich stars give false impression of
# of lines in metal-poor abundance work!
heavy n-cap = rare-earth
Fe-peak
α, etc.
For Fe-peak elements
#/species <10 in most cases
light n-cap
3rd peak, Th
The reality is grim for metal-poor turnoff stars
AND, can you believe ANY past analysis??
the outcome for Bergemann et al.?
Comparison of low metallicity spectra
in the “visible” spectral region
a new attack: UV STIS spectra
The complex UV spectrum of HD 84937
dotted line, no Fe; solid line, best fit dashed lines: ±0.5 dex from best fit
red line, perfect agreement; other lines, deviations
Why is working in the UV a problem?
Opacity competition: metal-poor red giant
Opacity competition: metal-poor turnoff star
A summary of our results on Fe
probable
explanation of the
abundance “dip”
Other Fe-peak elements: a start
Or, [Co/Fe] ~ +0.3 from both of these neutral and ionized lines
Bergemann 2009: [Co/Fe] = +0.18 (LTE) = +0.66 (NLTE)
{probably ~+0.3 (LTE) on our [Fe/H] scale}
This rough cobalt estimate is not too bad …
HD 84937
the red line is the [Co/Fe] trend with [Fe/H] derived by
the “first stars” group (Cayrel et al. 2004)
work on Cr I and
Cr II is underway
Matt Alvarez, Chris Sneden (UT),
Jennifer Sobeck (U Chicago), Betsy
den Hartog, Jim Lawler (U Wisconsin)
Summary:
metal-poor stars hold keys to understanding Galactic nucleosynthesis
Atomic physics dictates “non-standard” wavelengths for some elements
STIS in the vacuum UV is the only choice for some poorly understood
element regimes
neutron-capture elements: observers are in the lead!
STIS is crucial for both lightest and heaviest stable elements
Fe-peak elements: theorists are in the lead!
No sane person should believe Fe-peak abundances right now
but STIS data hold promise for the near-future