the role of laboratory astrophysics in studies of fe-group nucleosynthesis in the early universe
DESCRIPTION
Talk given at the NASA Anuual UV-Vis SR&T Workshop, NASA Head Quarters, 20-21 September 2011.TRANSCRIPT
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The Role of Laboratory Astrophysicsin studies of Fe-group nucleosynthesis
in the early Universe
Betsy Den HartogUniv. of Wisconsin
Jim Lawler, Mike Wood, (U Wisc)Chris Sneden (U TX-Austin) John Cowan (U OK-Norman) Jennifer Sobeck (U Chicago)
+ other collaborators
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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!
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figure from:C. Sneden et al. ApJS 182:80 (2009)
last decade: n-capture abundances were dramatically improved with new log(gf) values.
figure from:J E Lawler et al ApJS 162:227 (2006)
Tightly defined r-process abundance pattern will constrain future modeling efforts.(Tens of person-years work underlie this plot.)
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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)
Fe-group abundance patterns are not well understood at low metallicity.
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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
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u
2
3
4
1
1/ττττu = ∑∑∑∑ Aui
Au1
BFuk = Auk / ∑∑∑∑ Aui
Auk = BFuk / ττττ u
Au2
Au3
Au4
Transition probabilities are determined by combining radiative lifetimes and branching fractions.
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Radiative Lifetimes are measured using time-resolved laser-induced fluorescence (LIF) on an atomic beam.
Lifetime Experiment Apparatus
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Aligning the laser with summer research student Ms. Allie Fittante
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Sample LIF radiative lifetime data for Mn I
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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
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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
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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.
HD 84937 Teff = 6275 K log(g) = 4.00 [Fe/H] = -2.10 Dwarf Star, Metal poor
Mn I linesMn II lines
Initial application of lab data (LTE/1D) shows interesting trend with excitation potential χχχχ.
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HD 115444 Teff = 4575 K log(g) = 1.25 [Fe/H] = -2.90Giant star, Metal poor
Mn II lines
Mn I lines
The trend with excitation potential χχχχ is even more pronounced at lower gravity.
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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
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BF measurements of weak lines will be tackled using an upgraded
Echelle spectrometer.
• 3m focal length, vacuum compatible echellespectrograph 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
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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
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Sample FTS data Ti II 3261.62 Åhollow cathode lamp 770 mA
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Sample echelle data Ti II 3261.62 Åhollow cathode lamp 10 mA
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Sample echelle data Ti II 3261.62 Åhollow cathode lamp 10 mA
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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