Research ArticleASTRONOMY

Late formation of silicon carbide in type II supernovae

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Science Advances  17 Jan 2018:
Vol. 4, no. 1, eaao1054
DOI: 10.1126/sciadv.aao1054
  • Fig. 1 Schematic diagram of the “onion-shell” internal structure of a pre-SN massive star.

    Zones are labeled by their most abundant elements (26). Neutron capture taking place in the outer C-rich He/C zone converts 28Si and 48Ti to neutron-rich Si and Ti isotopes, respectively, whereas α-capture in the inner Si/S zone overproduces α-nuclides, including 28Si and 48Ti. Abundant short-lived 49V is also made in the Si/S zone.

  • Fig. 2 Comparison of X grain data from this study with literature data.

    (A) δ49Ti versus 51V/48Ti, (B) δ49Ti versus δ30Si, and (C) 51V/48Ti versus δ30Si comparing presolar X grain data from this study (blue solid circles) with literature data [open symbols (23, 24, 31, 33, 35, 36)]. Analytical uncertainties are 1σ. Plotted in (B) are only literature data with analytical uncertainties in δ49Ti (1σ error < 100‰) comparable to those in this study. See the notation of Table 1 for definition of δ values.

  • Fig. 3 δ49Ti* versus δ30Si of the same set of X grains in Fig. 2 and three ungrouped SN grains.

    Note that the Lin et al. grain data (33) from Fig. 2 are not plotted here because of the lack of information on δ50Ti values in these grains. δ49Ti* denotes δ49Ti of a grain after substracting the amount of 49Ti made by neutron capture in the He/C zone (see the Supplementary Text). The negative trend shown as a linear fit line (red solid line) with 95% confidence (gray band) results from variable contributions from the He/C zone to the 48Ti and 30Si budgets of the grains (eq. S5). The fact that grains with δ30Si > ~−200‰ show constant δ49Ti* = −1000‰ (yellow region) means that the contributions from the Si/S zone are negligible in affecting the 48Ti budgets of these grains.

  • Fig. 4 Growth curves of δ49Ti in the Si/S zone resulting from 49V decay after the SN explosions (black lines with symbols) predicted by models for solar metallicity SNe with a range of progenitor masses.

    The numbers adjacent to the symbols denote the postexplosion times. The δ49TiSi/S value obtained by the linear fit in Fig. 3 is shown (red line) with 95% confidence (gray band).

  • Table 1 Carbon, N, Si, Al, and Ti isotopic compositions of type X SiC grains in Murchison.

    Uncertainties are 1σ. A, agglomerate-like morphology; S, single grains. Four grains had too low Ti concentrations so that their Ti isotope ratios could not be determined.

    GrainSize
    (μm)
    Morphology12C/13C14N/15Nδ29Si*
    (‰)
    δ30Si
    (‰)
    26Al/27Al
    (×1000)
    δ46Ti
    (‰)
    δ47Ti
    (‰)
    δ49Ti
    (‰)
    δ50Ti
    (‰)
    V/Ti
    M1-A3-G3201.6 × 2.8A224 ± 251 ± 1−273 ± 5−448 ± 8392 ± 339 ± 64113 ± 93400 ± 19228 ± 100.311
    M1-A7-G9611.1 × 1.0A164 ± 2113 ± 4−399 ± 5−544 ± 8268 ± 140 ± 47−6 ± 70350 ± 18−8 ± 80.094
    M1-A8-G1371.9 × 1.3A149 ± 265 ± 2−286 ± 6−445 ± 17350 ± 1−17 ± 72−84 ± 86402 ± 19206 ± 100.116
    M1-A9-G9211.3 × 1.2S211 ± 354 ± 1−316 ± 8−464 ± 12230 ± 1−4 ± 89−55 ± 103528 ± 21220 ± 120.054
    M2-A1-G4210.6 × 0.6S145 ± 4126 ± 3−237 ± 7−375 ± 15153 ± 245 ± 290 ± 32508 ± 21191 ± 110.273
    M2-A1-G6742.5 × 2.6A120 ± 387 ± 1−210 ± 6−290 ± 8303 ± 1−8 ± 17−23 ± 22304 ± 17198 ± 100.139
    M2-A1-G9042.6 × 2.7S100 ± 370 ± 1−168 ± 6−341 ± 12277 ± 115 ± 3713 ± 22261 ± 29186 ± 290.047
    M2-A1-G9742.1 × 2.5A139 ± 4116 ± 2−222 ± 6−343 ± 10203 ± 1−2 ± 27−6 ± 12158 ± 15188 ± 100.017
    M2-A2-G3730.9 × 0.9S149 ± 6−183 ± 17−186 ± 2539 ± 1−3 ± 5225 ± 76115 ± 15192 ± 100.130
    M2-A2-G10361.1 × 1.2S202 ± 7−404 ± 12−572 ± 15209 ± 171 ± 8523 ± 25417 ± 3598 ± 320.091
    M2-A3-G1203.7 × 3.7A82 ± 1−155 ± 6−240 ± 11306 ± 123 ± 6979 ± 93268 ± 17234 ± 100.169
    M2-A3-G10101.0 × 0.6S318 ± 12−291 ± 14−475 ± 11199 ± 141 ± 5555 ± 80685 ± 24119 ± 120.109
    M2-A3-G14671.0 × 1.1S105 ± 2−153 ± 7−265 ± 15225 ± 1101 ± 7863 ± 9794 ± 15127 ± 100.092
    M3-G5011.0 × 0.9S86 ± 238 ± 1−330 ± 15−480 ± 15126 ± 181 ± 13810 ± 149603 ± 21316 ± 110.067
    M3-G6911.6 × 1.6A36 ± 134 ± 1−216 ± 8−230 ± 8127 ± 1−19 ± 43−36 ± 44114 ± 15−31 ± 80.044
    M3-G13431.2 × 1.8S52 ± 1120 ± 4−106 ± 7−161 ± 78.0 ± 0.182 ± 56116 ± 83126 ± 41120 ± 410.049
    M2-A3-G430.8 × 0.8S81 ± 1−380 ± 7−500 ± 14367 ± 2
    M2-A3-G16830.7 × 0.8S54 ± 1−335 ± 6−430 ± 14307 ± 1
    M2-A4-G14330.8 × 0.8S104 ± 6−393 ± 19−424 ± 29200 ± 1
    M2-A5-G4120.9 × 1.2S67 ± 222 ± 1−237 ± 7−375 ± 15

    *δ notation is defined as δiA = [(iA/jA)grain/(iA/jA)std − 1] × 1000, where A denotes an element, i denotes an isotope of this element, and j denotes the normalization isotope, and (iA/jA)grain and (iA/jA)std represent the corresponding isotope ratios measured in a sample and the standard, respectively.

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/1/eaao1054/DC1

      Supplementary Text

      fig. S1. Silicon three-isotope plot comparing 62 X grains found on the three gold mounts to the 20 X grains and two ungrouped grains chosen for Ti-V isotope analysis in this study.

      fig. S2. R2 for the correlation between the δ49Ti* and δ30Si values of X grains versus the 49Ti/50Ti production ratios in the He/C zone showing that the smaller the production ratio, the lower the R2 value.

      fig. S3. The same as Fig. 3 but with δ49Ti* calculated by adopting a 49Ti/50Ti production ratio of 0.50 instead of 1.04.

      fig. S4. δ49Ti (upper panel) and 51V/48Ti (lower panel) versus NanoSIMS analysis cycle showing the inclusion of a Ti- and V-rich subgrain (gray region) within X grain M1-A8-G138, which had enhanced V/Ti ratios but no concomitant increase in δ49Ti within analytical uncertainties (~100‰), indicating incorporation of a negligible amount of live 49V, that is, formation after the decay of the majority of live 49V in the Si/S zone.

      table S1. Carbon, N, Si, Al, K-Ca, and Ca-Ti isotopic compositions of two ungrouped SiC grains and one ungrouped graphite, KE3d-9 (38), separated from Murchison.

    • Supplementary Materials

      This PDF file includes:

      • Supplementary Text
      • fig. S1. Silicon three-isotope plot comparing 62 X grains found on the three gold mounts to the 20 X grains and two ungrouped grains chosen for Ti-V isotope analysis in this study.
      • fig. S2.R2 for the correlation between the δ49Ti* and δ30Si values of X grains versus the 49Ti/50Ti production ratios in the He/C zone showing that the smaller the production ratio, the lower the R2 value.
      • fig. S3. The same as Fig. 3 but with δ49Ti* calculated by adopting a 49Ti/50Ti production ratio of 0.50 instead of 1.04.
      • fig. S4. δ49Ti (upper panel) and 51V/48Ti (lower panel) versus NanoSIMS analysis cycle showing the inclusion of a Ti- and V-rich subgrain (gray region) within X grain M1-A8-G138, which had enhanced V/Ti ratios but no concomitant increase in δ49Ti within analytical uncertainties (~100‰), indicating incorporation of a negligible amount of live 49V, that is, formation after the decay of the majority of live 49V in the Si/S zone.
      • table S1. Carbon, N, Si, Al, K-Ca, and Ca-Ti isotopic compositions of two ungrouped SiC grains and one ungrouped graphite, KE3d-9 (38), separated from Murchison.

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