Isotopic properties of silicon carbide X grains from the Murchison meteorite in the size range 0.5-1.5 μm

Details Isotopic properties of silicon carbide X grains from the Murchison meteorite in the size range 0.5-1.5 μm Isotopic properties of silicon carbide X grains from the Murchison meteorite in the size range 0.5-1.5 μm

Nov 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000m%26ps...35.1157h&link_type=abstract

Meteoritics & Planetary Science, vol. 35, no. 6, pp. 1157-1176 (2000).

Computer Science

65

Scientific paper

We report isotopic abundances for C, N, Mg-Al, Si, Ca-Ti, and Fe in 99 presolar silicon carbide grains of type X (84 grains from this work and 15 grains from previous studies) from the Murchison CM2 meteorite, ranging in size from 0.5 to 1.5 μm. Carbon was measured in 41 X grains, N in 37 grains, Mg-Al in 18 grains, Si in 87 grains, Ca-Ti in 25 grains, and Fe in 8 grains. These X grains have 12C/13C ratios between 18 and 6,800, 14N/15N ratios from 13 to 200, ???Si/28Si between -750 and +60 deg, ???Si/28Si from -770 to -10 deg, and 54Fe/56Fe ratios that are compatible with solar within the analytical uncertainties of several 10 percent. Many X grains carry large amounts of radiogenic 26Mg (from the radioactive decay of 26Al, half life ( 7 105 a) and radiogenic 44Ca (from the radioactive decay of 44Ti, half life = 60 a). While all X grains but one have radiogenic 26Mg, only about 20 percent of them have detectable amounts of radiogenic 44Ca. Initial 26Al/27Al ratios of up to 0.36 and initial 44Ti/48Ti ratios of up to 0.56 can be inferred. The isotopic data are compared with those expected from the potential stellar sources of silicon carbide dust. Carbon stars, Wolf-Rayet stars, and novae are ruled out as stellar sources of the X grains. The isotopic compositions of C and Fe and abundances of extinct 44Ti are well explained both by type Ia and type II supernova (SN) models. The same holds for 26Al/27Al ratios except for the highest 26Al/27Al ratios of > 0.2 in some X grains. Silicon agrees qualitatively with SN model predictions but the observed 29Si/30Si ratios in the X grains are in most cases too high, pointing to deficiencies in the current understanding of the production of Si in SN environments. The measured 14N/15N ratios are lower than those expected from SN mixing models. This problem can be overcome in a 15 M_sun type II SN if rotational mixing and/or preferential trapping of N from 15N-rich regions in the ejecta is considered. The isotopic characteristics of C, N, Si and initial 26Al/27Al ratios in small X grains are remarkably similar to those of large X grains (2-10 ?m). Titanium-44 concentrations are generally much higher in smaller grains, indicative of the presence of Ti-bearing subgrains that might have served as condensation nuclei for silicon carbide. The fraction of X grains among presolar silicon carbide is largely independent of grain size. This implies similar grain size distributions for silicon carbide from carbon stars (mainstream grains) and supernovae (X grains), a surprising conclusion in view of the different conditions for dust formation in these two types of stellar sources.

Affiliated with

Also associated with

No associations

Rating

Isotopic properties of silicon carbide X grains from the Murchison meteorite in the size range 0.5-1.5 μm 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 Isotopic properties of silicon carbide X grains from the Murchison meteorite in the size range 0.5-1.5 μm, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Isotopic properties of silicon carbide X grains from the Murchison meteorite in the size range 0.5-1.5 μm will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1613930