Talk given at the NASA Anuual UV-Vis SR&T Workshop, NASA Head Quarters, 20-21 September 2011.

1. The Role of Laboratory Astrophysics
in studies of Fe-group nucleosynthesis
in the early Universe
Betsy Den Hartog
Univ. of Wisconsin
Jim Lawler, Mike Wood, (U Wisc)
Chris Sneden (U TX-Austin)
John Cowan (U OK-Norman)
Jennifer Sobeck (U Chicago)
+ other collaborators

2. Extended life of HST is an opportunity for
studies of Fe-group nucleosynthesis
in the early Galaxy
• Hubble properties make it ideal for these studies:
- access to UV region
- high spectral resolving power
- good sized primary
• UW group - strong collaboration with Chris Sneden
(UT-Austin), John Cowan (U OK-Norman),….
• study of metal-poor halo stars sheds light on the
early times of galactic history
• abundance patterns of many n-capture elements are
now better than Fe-group!

3. last decade: n-capture abundances were
dramatically improved with new log(gf) values.
Tightly defined r-process abundance pattern
will constrain future modeling efforts.
(Tens of person-years work underlie this plot.)
figure from: figure from:
J E Lawler et al ApJS 162:227 (2006) C. Sneden et al. ApJS 182:80 (2009)

4. Fe-group abundance patterns are not well
understood at low metallicity.
Relative Co to Cr abundance [Co/Cr] normalized to the Solar abundance of these
elements as a function of metallicity [Fe/H] normalized to the Solar metalicity for a
large set of stars. (Plot prepared and provided by Prof. John Cowan and Jason Collier, Univ. of
Oklahoma)

5. Fe-group synthesis in the
early Universe
• Relative Fe-group abundances are not
understood!
• Is this a non-LTE photospheric effect?
• Nuclear physics effect?
• Is this an effect from cumulative errors in lab
data (f-values) as abundance determinations
switch from line-to-line to study lower and
lower metallicity stars?
• New Fe-group transition probability effort will
help shed light on these questions

6. Transition probabilities are determined by
combining radiative lifetimes and branching
fractions. u
Au4
Au3
Au2
4 Au1
3 τ
1/τu = ∑ Aui
2
BFuk = Auk / ∑ Aui
1 Auk = BFuk / τ u

7. Radiative
Lifetimes are
measured
using time-
resolved laser-
induced
fluorescence Lifetime Experiment Apparatus
(LIF) on an
atomic beam.

8. Aligning the laser with summer research
student Ms. Allie Fittante

9. Sample LIF radiative lifetime data for Mn I

10. Branching Fractions are determined
from high-resolution FTS spectra
Advantages of an FTS
• Very high spectral resolving power
• Excellent absolute wavenumber accuracy
• Very high data collection rates
• Large etendue
• Insensitive to source intensity drifts

11. We have recently completed
lab work on Mn I and Mn II.
• We reported some of the most accurate f-values
available for Fe – group species
• Multiplets were carefully selected so that
branching fraction uncertainties could be
minimized
• reduced uncertainty of radiative lifetimes using
new benchmark lifetimes Mg+, Na to accurately
characterize residual systematics
• log(gf) ± 0.02 dex with high (2 sigma) confidence

13. Initial application of lab data (LTE/1D) shows
interesting trend with excitation potential χ.
HD 84937 Teff = 6275 K log(g) = 4.00 [Fe/H] = -2.10
Dwarf Star, Metal poor
Mn II lines
Mn I lines
The lines with excitation potential near 7 eV connect to the
ground level of the ion (Mn II resonance lines). Nearly all
the photospheric Mn resides in that level and non-LTE
effects are negligible.

14. The trend with excitation potential χ is even
more pronounced at lower gravity.
HD 115444 Teff = 4575 K log(g) = 1.25 [Fe/H] = -2.90
Giant star, Metal poor
Mn I lines
Mn II lines

15. Choice of transition is critical in abundance
determinations in the Fe-group.
• UV lines to the ground and low metastable levels
of the ion are the most reliable abundance
probes - insensitive to non-LTE effects
• For Fe–group species, weak lines are the best,
insensitive to microturbulance
• FTS instruments have many advantages, but are
not ideal for weak lines due to multiplex noise:
photon noise from every line in a wide spectrum
is redistributed evenly throughout the spectrum

16. BF measurements of weak lines
will be tackled using an upgraded
Echelle spectrometer.
• 3m focal length, vacuum compatible echelle
spectrograph acquired in the 1990s for NASA
work on VUV ion lines used for ISM studies
• New grating: 23.2 groove/mm, 63º blaze, 135 x
265 mm2
• Custom designed prismatic order separator
• Aberration compensated
• UV sensitive 4 Mpix CCD, 13.5 micron pix

18. Echelle spectrometer performance
• resolving power ~ 100,000
• broad UV coverage, 2000 Å - 4000 Å in 3
CCD frames with no gaps
• UV sensitivity excellent, low current
optically thin lamps give good S/N
• no multiplex noise of FTS instruments
• main disadvantage compared to FTS:
wavelength calibration is not as good

19. Sample FTS data Ti II 3261.62 Å
hollow cathode lamp 770 mA

20. Sample echelle data Ti II 3261.62 Å
hollow cathode lamp 10 mA

21. Sample echelle data Ti II 3261.62 Å
hollow cathode lamp 10 mA

22. Near Term Goals of Wisconsin
Laboratory Astrophysics Program
• eliminate lab data as major source of
uncertainties in the Fe-group abundance
patterns of metal poor stars (new and
archived HST UV data is crucial)
• provide f-values for weak lines connecting
to ground state of dominant species - these
lines should be reliable abundance probes