Showing papers by "Gary R. Huss published in 2007"

Titanium isotopic compositions of well-characterized silicon carbide grains from Orgueil (CI): Implications for s-process nucleosynthesis

Abstract: We have measured the titanium isotopic compositions of 23 silicon carbide grains from the Orgueil (CI) carbonaceous chondrites for which isotopic compositions of silicon, carbon, and nitrogen and aluminum-magnesium systematics had been measured previously. Using the 16 mostprecise measurements, we estimate the relative contributions of stellar nucleosynthesis during the asymptotic giant branch (AGB) phase and the initial compositions of the parent stars to the compositions of the grains. To do this, we compare our data to the results of several published stellar models that employ different values for some important parameters. Our analysis confirms that s-process synthesis during the AGB phase only slightly modified the titanium compositions in the envelopes of the stars where mainstream silicon carbide grains formed, as it did for silicon. Our analysis suggests that the parent stars of the >1 μm silicon carbide grains that we measured were generally somewhat more massive than the Sun (2-3 Mʘ) and had metallicities similar to or slightly higher than solar. Here we differ slightly from results of previous studies, which indicated masses at the lower end of the range 1.5-3 Mʘ and metallicities near solar. We also conclude that models using a standard 13C pocket, which produces a good match for the main component of s-process elements in the solar system, overestimate the contribution of the 13C pocket to s-process nucleosynthesis of titanium found in silicon carbide grains. Although previous studies have suggested that the solar system has a significantly different titanium isotopic composition than the parent stars of silicon carbide grains, we find no compelling evidence that the Sun falls off of the array defined by those stars. We also conclude that the Sun does lie on the low-metallicity end of the silicon and titanium arrays defined by mainstream silicon carbide grains.

On the Nature and Origins of Type II Chondrules from CR2 Chondrites

Abstract: Jr., M. K. Weisberg, G. R. Huss, K. Nagashima, D. S. Ebel, D. L. Schrader and D. S. Lauretta3.Dept. Physical Sciences, Kingsborough College of the City University of New York, Brooklyn NY 100235, USA (hconnolly@kbcc.cuny.edu); Dept. Earth and Planetary Sciences, American Museum of Natural History (AMNH), New York, NY 110024, USA; 3 Lunar and Planetary Laboratory (LPL), University of Arizona, Tucson, AZ 85721, USA; Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Manoa, Honolulu, HI 96822, USA.

The Birth Environment of the Solar System Inferred from a "Mixing-Fallback" Supernova Model

Abstract: Ipatov S. I. Boss A. P. Myhill E. A. Triggering Presolar Cloud Collapse and Injection of Short-lived Radioisotopes by a Supernova Shock Wave: Adaptive Mesh Refinement Calculations with the FLASH Code [#1018] We are using the adaptive mesh refinement code FLASH in order to calculate improved hydrodynamical models of the interaction of a supernova shock wave with the presolar cloud, to learn if triggering of collapse and injection can occur simultaneously.

Contribution of a "Mixing-Fallback" Supernova to Short-Lived Radionuclides in the Solar System

Abstract: Introduction: The former presence of short-lived radionuclides (SLRs) in the early solar system ( 10 Be, 26 Al, 36 Cl, 41 Ca, 53 Mn, 60 Fe, 107 Pd, 129 I, and 182 Hf) is inferred from excesses in the abundances of their daughter nuclides in meteorites, linearly correlated with the abundances of parent elements [e.g.,1]. SLRs with mean lives <5 Myr can be produced either by energetic-particle irradiation or by stellar nucleosynthesis. Solar energetic-particle irradiation can produce the required amount of 10 Be and probably some other SLRs [2], but cannot produce the estimated initial abundance of 60 Fe in the solar system [3-5]. Because 60 Fe is produced efficiently only in stars, and its estimated abundance in the solar system cannot be explained by the steady-state abundance of 60 Fe in the interstellar medium, stellar nucleosynthesis prior to or shortly after the solar system formation should have contributed to the inventory of the solar-system SLRs. Several attempts have been made to find a suitable stellar source for the solar-system SLRs [e.g., 6-8]. Low-mass AGB stars produce insufficient amounts of 60 Fe [e.g., 8]. Models for intermediate-mass AGB stars may explain the abundances of 26 Al, 41 Ca and 60 Fe [8], but the rarity of encounters between molecular clouds and AGB stars [9] makes it implausible for an AGB star to be a source of SLRs in the solar system. Several nucleosynthetic models for SNe II [e.g., 10-13] indicate that 60 Fe may have been overproduced if all the 26 Al and 41 Ca in the solar system were provided by a SN II. Moreover, the abundance of 53 Mn inferred for SNe II is 10-100 times larger than that in the solar system. If a massive star exploded with less kinetic energy, most of 53 Mn synthesized in the incomplete Siburning layer may have undergone fallback onto a collapsing stellar core [12]. If this is the case, 53 Mn in the solar system should have been derived from another source, i.e., the continuous galactic nucleosynthesis. In this study, as a potential stellar source of SLRs with <5 Myr ( 26 Al, 41 Ca, 53 Mn, and 60 Fe) in the early solar system, we propose a SN II with mixing-fallback, where the inner region of the exploding star experienced mixing, some fraction of mixed materials is ejected, and the rest undergoes fallback onto the core [e.g., 13]. The mixing-fall back model well reproduces the abundance pattern of hyper metal-poor stars [13]. Methods: We calculated yields of nuclides in the ejecta from a SN II with mixing-fallback based on the nucleosynthesis model for a solar-metallicity massive star with the kinetic energy of explosion of 10 51 erg [13] using the mass of the inner mixing region (Mmix) and the fraction of materials ejected from the mixing region (q) as parameters. We assumed that the ejecta was mixed with protosolar materials (or the protoplanetary disk) with a dilution factor of f0, and that there was a time interval of between the SN II nucleosynthesis and the formation of the oldest solid objects in the solar system [6-8]. The f0 and were determined to minimize deviations of calculated abundances of 26 Al, 41 Ca, 53 Mn, and 60 Fe from their estimated initial abundances in the solar system. The abundance of 36 Cl was also calculated using determined f0 and to compare with the reported lower limit of 36 Cl abundance in the solar system. The cases for SNe II without mixing-fallback were calculated based on the models by [10-13] as well. Results: Figure 1 shows calculated initial abundances for the solar system of 26 Al, 36 Cl, 41 Ca, 53 Mn, and 60 Fe as a function of the mass of the exploding star. The abundances of SLRs inferred in non-fallback models are also shown for comparison. Compared to non-fallback models, where 53 Mn is overproduced and 26 Al is underproduced, the inferred abundances of 26 Al, 36 Cl, 41 Ca, 53 Mn, and 60 Fe in mixing-fallback models agree with their estimated solar-system abundances within a factor of 3 if mixing occurs within the C/O burning layer and the ejection fraction q of the mixed material is 0.001-0.01 (Fig. 2). However, if mixing occurs in the He-burning layer as well, i.e., larger Mmix, 53 Mn is overproduced and 60 Fe is underproduced (Fig. 2). If degree of mixing is small and mixing occurs only within the Si-burning layer, 53 Mn is overproduced and 26 Al is underproduced, as in the case for nonfallback models (Fig. 2). Note that the solar-system abundances of SLRs are well reproduced in a wide range of masses of the star (20-40 MSun) as long as the mixing-fallback occurs within the C/O burning layer. The f0 varies from ~10 -5 for smaller Mmix to ~10 -3