Low-Density Graphite Grains and Mixing in Type II Supernovae

Details Low-Density Graphite Grains and Mixing in Type II Supernovae Low-Density Graphite Grains and Mixing in Type II Supernovae

Jan 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...510..325t&link_type=abstract

The Astrophysical Journal, Volume 510, Issue 1, pp. 325-354.

Astronomy and Astrophysics

Astronomy

103

Ism: Dust, Extinction, Nuclear Reactions, Nucleosynthesis, Abundances, Supernovae: General

Scientific paper

Primitive meteorites contain presolar grains that originated in stellar outflows and supernova ejecta. Low-density graphite grains from the Murchison carbonaceous meteorite were analyzed for the isotopic compositions of C, N, O, Mg, Si, K, Ca, and Ti by ion microprobe mass spectrometry. The grains are characterized by a large range of ^12C/^13C ratios (from 3.6 to 7200 compared to the solar ratio of 89), excesses in ^15N (^15N/^14N up to 10 times solar) and ^18O (^18O/^16O up to 185 times solar), large inferred ^26Al/^27Al ratios (from ^26Mg excesses) ranging up to 0.15, a large range in Si isotopic ratios (from 50% deficits in ^29Si and ^30Si relative to ^28Si up to more than 120% excesses), large excesses in ^41K and ^44Ca from the prior presence of now-extinct ^41Ca (T_1/2=10^5 yr) and ^44Ti (T_1/2=59 yr), respectively, and excesses in ^42Ca, ^43Ca relative to ^40Ca, and ^49Ti, and ^50Ti relative to ^48Ti. Several of these isotopic signatures indicate a supernova origin. In particular, the initial presence of ^44Ti and excesses of ^28Si as well as the size of the inferred ^41Ca/^40Ca ratios are proof that the carrier grains formed in supernova ejecta. We explored the possibility that the low-density graphite grains originated from C-rich ejecta of Type II supernovae. In such stars ^44Ti and ^28Si are produced in the inner layers and the presence of these two isotopes in carbonaceous grains is evidence for extensive mixing of different supernova layers in the explosion. We performed mixing calculations of different layers of the SN models by Woosley & Weaver under the imposed boundary condition that C>=O and compare the resulting isotopic ratios with the isotopic ratios measured in the meteoritic grains. The mixing model can explain the observed ^12C/^13C, ^16O/^18O, ^30Si/^28Si, and ^44Ti and ^41Ca fairly well as long as jets of material from the Si-rich zone, carrying ^44Ti and pure ^28Si, are assumed to penetrate the O-rich zone and are ejected into and mixed with the C-rich layers, where carbonaceous grains can form, without overwhelming these layers with the massive amounts of oxygen. Problems with the model are that it produces not enough ^15N and consistently yields lower ^29Si/^30Si ratios than those in the grains. Furthermore, large excesses in ^42Ca and ^50Ti found in several grains, which can be attributed to neutron capture, in the model are obtained only in layers with O>C. It remains to be seen whether adjustment of cross sections and/or multidimensional SN models can overcome some of these problems. It also remains to be seen whether Type Ia supernovae, which have been proposed as a source of SN grains in meteorites, can provide a better explanation. The fact that essentially all supernova grains identified so far are diamond, graphite, SiC of Type X and Si_3N_4, and only one oxide grain with a supernova signature has been found remains a puzzle.

Affiliated with

Also associated with

No associations

Rating

Low-Density Graphite Grains and Mixing in Type II Supernovae does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Low-Density Graphite Grains and Mixing in Type II Supernovae, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low-Density Graphite Grains and Mixing in Type II Supernovae will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1189890