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] = log 10 (N A /N B ) star – log 10 (N A /N B ) Sun log ε(A) = log 10 (N A /N H ) (spectroscopic) log N(A) = log 10 (N A /N Si ) (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 3 rd neutron-capture peak Understudied lighter neutron-capture elements Fe-group elements Light elements (Be, B)

The ultimate question? How did our Galaxy produce the solar chemical composition? SCG08 = Sneden, Cowan, & Gallino 2008, ARA&A, 46, 241

Most isotopes of elements with Z>30 are formed by: A Z + n A+1 Z Followed by, for unstable nuclei: A+1 Z A+1 (Z+1) +  - RbSrYZrNbMoTcRuRhPdAgCdInSnSbTeI ScCaK Xe TiVCrMnFeCoNiCuZnGaGeAsSeBrKr H BeLi Mg Na HfTaWReOsIrPtAuHgTlPbBiPoAtRn RaFr BaCs RfDbSgBhHsMtUunUuuUub CBOFNe ArAlSiPSCl N He LaCePrNdPmSmEuGdTbDyHoErTmYbLu AcThPaUNpPuAmCmBkCfEsFmMdNoLr First discussion: n(eutron)-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) Buildup of n-capture elements

A detailed look at the r- and s-process paths SCG08 “s-process” element “r-process” element

n-capture spectra of metal-poor stars HD : [Fe/H] = -2.7 T eff ~ 4750 LOW n-capture CS : [Fe/H] = -3.1 T eff ~ 4750 HIGH n-capture

“r-process-rich” metal-poor stars first example, HD , was reported by Griffin et al SCG08 An important abundance ratio: log  (La/Eu) = +0.6 (solar total) = +0.2 (solar r-only) = +1.5 (solar s-only)

HfBa LaCePrNdPmSmEuGdTbDyHoErTmYbLu Wisconsin lab studies: log gf and hyperfine/isotopic structure Lawler et al. 2000a Lawler et al Lawler et al. 2000b Lawler et al Lawler et al Lawler et al Lawler et al Den Hartog et al Lawler et al Sneden et al Sun: # transitions used in analysis CS : # transitions used in analysis why are rare earths well understood? (unstable element)(well studied in literature)

n-capture compositions of well- studied r-rich stars: Così fan tutte?? SCG08 lines are solar-system abundances differences from solar-system means of the differences

Thorium/Uranium detections promise alternate Galactic ages Frebel et al. 2007

leading to possible radioactive decay ages U/Th ratio should be best age indicator, if both elements can be detected reliably Persistent question: why is Pb usually low? 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

Johnson & Bolte 2002 Beyond simplest results: de-coupling of the heavy/light r-process elements See also Aoki et al. 2005, 2007 Z Y = 39 Z Ba = 56

r-process abundance distribution variations: "normal" Roederer et al 2010

But various densities must contribute to r-process Kratz et al increasing density componentsdecreasing density components

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

All reasonably strong lines are in the vacuum UV; this is why STIS is good here Niobium: here is why there are difficulties Nilsson et al. 2010

UV spectra of 3 metal-poor giants Roederer et al 2010 HD : [Fe/H] = -2.7 T eff ~ 4750 LOW n-capture HD : [Fe/H] = -2.9 T eff ~ 4650 HIGH n-capture BD [Fe/H] = -2.2 T eff ~ 5200 HIGH n-capture

Initial STIS exploration HD : [Fe/H] = -2.7 T eff ~ 4750 LOW n-capture HD : [Fe/H] = -2.9 T eff ~ 4650 HIGH n-capture CS [Fe/H] = -3.1 T eff ~ 4750 HIGH n-capture Cowan et al. 2005

Heaviest stable elements scale with Eu Cowan et al Again, Eu is the usual “pure” r-process element

But light n-capture elements do NOT scale with Eu Cowan et al. 2005

Upon further review of these same STIS data … Roederer et al 2010 Points = data Lines = syntheses: best fit (color) ± 0.3dex (dotted) no element (solid)

Helps “complete” the n-capture distribution Roederer et al 2010 Points = observations Blue line = SN ν wind Farouqi et al Gray lines = scaled solar-system

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 Kobayashi et al (following Timmes et al. 1995) crucial distinction from n-capture elements: the Fe-peak element productions can actually be predicted theoretically

for some elements, all seems well Kobayashi et al (solid line new results

but for others, discomfort Kobayashi et al neutral lines ionized lines same predicted Cr abundances

should be simple to do Fe-peak elements: their abundances >> n-capture ones

Fe-peak light n-cap heavy n-cap = rare-earth 3 rd peak, Th α, etc. r-process-rich stars give false impression of # of lines in metal-poor abundance work! For Fe-peak elements #/species <10 in most cases

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] = (LTE) = (NLTE) {probably ~+0.3 (LTE) on our [Fe/H] scale}

This rough cobalt estimate is not too bad … the red line is the [Co/Fe] trend with [Fe/H] derived by the “first stars” group (Cayrel et al. 2004) HD 84937

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