Early Galactic Nucleosynthesis: The Impact of HST/STIS Spectra of Metal-Poor Stars

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Early Galactic Nucleosynthesis: The Impact of HST/STIS Spectra of Metal-Poor Stars. Chris Sneden University of Texas. 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 - PowerPoint PPT Presentation

Transcript of Early Galactic Nucleosynthesis: The Impact of HST/STIS Spectra of Metal-Poor Stars

  • Early Galactic Nucleosynthesis: The Impact ofHST/STIS Spectra of Metal-Poor StarsChris SnedenUniversity of Texas

  • A Very Collaborative Effort

    Definitions:[A/B] = log10(NA/NB)star log10(NA/NB)Sunlog (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-peakthe common thread: nucleosynthesis at the end of stellar lives

  • HST/STIS spectra: relevant to entire nuclide range Heaviest stable elementsa.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

  • Most isotopes of elements with Z>30 are formed by: AZ + n A+1ZFollowed by, for unstable nuclei: A+1Z A+1(Z+1) + b-RbSrYZrNbMoTcRuRhPdAgCdInSnSbTeIScCaKXeTiVCrMnFeCoNiCuZnGaGeAsSeBrKrHBeLiMgNaHfTaWReOsIrPtAuHgTlPbBiPoAtRnRaFrBaCsRfDbSgBhHsMtUunUuuUubCBOFNeArAlSiPSClNHeLaCePrNdPmSmEuGdTbDyHoErTmYbLuAcThPaUNpPuAmCmBkCfEsFmMdNoLrFirst discussion: n(eutron)-capture elements

  • s-process: -decays occur between successive n-capturesr-process: rapid, short-lived neutron blast temporarily overwhelms -decay ratesr- 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 pathsSCG08s-process elementr-process element

  • n-capture spectra of metal-poor starsHD 122563:[Fe/H] = -2.7Teff ~ 4750LOW n-capture

    CS 22892-052:[Fe/H] = -3.1Teff ~ 4750HIGH n-capture

  • r-process-rich metal-poor starsfirst example, HD 115444, was reported by Griffin et al. 1982SCG08An important abundance ratio:log e(La/Eu) = +0.6 (solar total) = +0.2 (solar r-only) = +1.5 (solar s-only)

  • HfBaLaCePrNdPmSmEuGdTbDyHoErTmYbLuWisconsin lab studies: log gf and hyperfine/isotopic structureLawler et al. 2000aLawler et al. 2001Lawler et al. 2000bLawler et al. 2004Lawler et al. 2006Lawler et al. 2007Lawler et al. 2008Den Hartog et al. 2003Den Hartog et al. 2003Lawler et al. 2009Sneden et al. 2009Sneden et al. 2009Sneden et al. 2009Sneden et al. 2009Sneden et al. 20091436142021338311445546Sun: # transitions used in analysis153215472913216183755932CS 22892-052 : # 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: Cos fan tutte?? SCG08lines are solar-system abundancesdifferences fromsolar-systemmeans of the differences

  • Thorium/Uranium detections promise alternate Galactic agesFrebel et al. 2007

  • leading to possible radioactive decay agesU/Th ratio should be best age indicator, if both elements can be detected reliablyPersistent question: why is Pb usually low?Frebel et al. 2007

  • good abundances really confront r-process predictionsIvans et al. 2006

  • But! crucial element groups for further progressIvans et al. 2006

  • Johnson & Bolte 2002Beyond simplest results: de-coupling of the heavy/light r-process elementsSee also Aoki et al. 2005, 2007ZY = 39ZBa = 56

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

  • But various densities must contribute to r-processKratz et al. 2007increasing 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 casesNilsson et al. 2010

  • All reasonably strong lines are in the vacuum UV; this is why STIS is good hereNiobium: here is why there are difficultiesNilsson et al. 2010

  • UV spectra of 3 metal-poor giantsRoederer et al 2010HD 122563:[Fe/H] = -2.7Teff ~ 4750LOW n-capture

    HD 115444:[Fe/H] = -2.9Teff ~ 4650HIGH n-capture

    BD+17 3248[Fe/H] = -2.2Teff ~ 5200HIGH n-capture

  • Initial STIS explorationHD 122563:[Fe/H] = -2.7Teff ~ 4750LOW n-capture

    HD 115444:[Fe/H] = -2.9Teff ~ 4650HIGH n-capture

    CS 22892-052[Fe/H] = -3.1Teff ~ 4750HIGH n-captureCowan et al. 2005

  • Heaviest stable elements scale with EuCowan et al. 2005Again, Eu is the usual pure r-process element

  • But light n-capture elements do NOT scale with EuCowan et al. 2005

  • Upon further review of these same STIS data Roederer et al 2010Points = data

    Lines = syntheses:best fit (color) 0.3dex (dotted)no element (solid)

  • Helps complete the n-capture distributionRoederer et al 2010Points = observations

    Blue line = SN windFarouqi et al. 2009

    Gray lines = scaled solar-system

  • Second discussion: back to the Fe-peakMcWilliam 1997

  • sharpening & extension by First Stars groupCayrel et al. 2004

  • elements that can be directly predicted in SNe modelsKobayashi et al. 2006 (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 wellKobayashi et al. 2006(solid line new results

  • but for others, discomfortKobayashi et al. 2006neutral linesionized linessame predicted Cr abundances

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

  • Fe-peaklight n-capheavy n-cap = rare-earth3rd peak, Th, etc.r-process-rich stars give false impression of # of lines in metal-poor abundance work!For Fe-peak elements #/species
  • 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 fitred 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 startOr, [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 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 underwayMatt Alvarez, Chris Sneden (UT), Jennifer Sobeck (U Chicago), Betsy den Hartog, Jim Lawler (U Wisconsin)

  • Summary:metal-poor stars hold keys to understanding Galactic nucleosynthesisAtomic physics dictates non-standard wavelengths for some elementsSTIS in the vacuum UV is the only choice for some poorly understood element regimesneutron-capture elements: observers are in the lead!STIS is crucial for both lightest and heaviest stable elementsFe-peak elements: theorists are in the lead!No sane person should believe Fe-peak abundances right nowbut STIS data hold promise for the near-future

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