{sup 26}Al AND THE FORMATION OF THE SOLAR SYSTEM FROM A MOLECULAR CLOUD CONTAMINATED BY WOLF-RAYET WINDS
- Department of Geology and Geophysics, University of Hawaii, Honolulu, HI 96822 (United States)
- Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, HI 96822 (United States)
- Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States)
In agreement with previous work, we show that the presence of the short-lived radionuclide (SLR) {sup 26}Al in the early solar system was unlikely (less than 2% a priori probability) to be the result of direct introduction of supernova (SN) ejecta into the gaseous disk during the Class II stage of protosolar evolution. We also show that Bondi-Hoyle accretion of any contaminated residual gas from the Sun's natal star cluster contributed negligible {sup 26}Al to the primordial solar system. Our calculations are consistent with the absence of the oxygen isotopic signature expected with any late introduction of SN ejecta into the protoplanetary disk. Instead, the presence of {sup 26}Al in the oldest solar system solids (calcium-aluminum-rich inclusions (CAIs)) and its apparent uniform distribution with the inferred canonical {sup 26}Al/{sup 27}Al ratio of (4.5-5) x 10{sup -5} support the inheritance of {sup 26}Al from the Sun's parent giant molecular cloud. We propose that this radionuclide originated in a prior generation of massive stars that formed in the same molecular cloud and contaminated that cloud by Wolf-Rayet winds. We calculated the Galactic distribution of {sup 26}Al/{sup 27}Al ratios that arise from such contamination using the established embedded cluster mass and stellar initial mass functions, published nucleosynthetic yields from the winds of massive stars, and by assuming rapid and uniform mixing into the cloud. Although our model predicts that the majority of stellar systems contain no {sup 26}Al from massive stars, and that the a priori probability that the {sup 26}Al/{sup 27}Al ratio will reach or exceed the canonical solar system value is only {approx}6%, the maximum in the distribution of nonzero values is close to the canonical {sup 26}Al/{sup 27}Al ratio. We find that the Sun most likely formed 4-5 million years (Myr) after the massive stars that were the source of {sup 26}Al. Furthermore, our model can explain the initial solar system abundance of a second, co-occurring SLR, {sup 41}Ca, if {approx}5 x 10{sup 5} yr elapsed between ejection of the radionuclides and the formation of CAIs. The presence of a third radionuclide, {sup 60}Fe, can be quantitatively explained if (1) the Sun formed immediately after the first SNe from the earlier generation of stars; (2) only 5% of SN ejecta was incorporated into the molecular cloud, or (3) the radionuclide originated in an even earlier generation of stars whose contributions to other radionuclides with a shorter half-life had completely decayed.
- OSTI ID:
- 21300663
- Journal Information:
- Astrophysical Journal, Vol. 696, Issue 2; Other Information: DOI: 10.1088/0004-637X/696/2/1854; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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