Yield stellar

Classical astronomy is largely concerned with the classification of stars without regard to the details of their constituent plasmas (63). Only more recently have sateUite-bome observations begun to yield detailed data from the high temperature regions of other stellar plasmas. Cosmic plasmas of diverse size scales have been discussed (64). 

Fig. 3. Variation as a function of the initial mass of the stellar yields in 14N for different Z and rotation velocities. At Z = 1CPB, the lowest continuous line is for r>ini = 0, the upper line for 300 km/s. At higher Z, rotation makes little differences, see also [10].

Fig. 2 shows [Pd/Ba] as a function of [Sr/Ba] with our new data by Subaru HDS. By definition, [Sr/Ba] should increase with the fractional contribution of weak r-process to the stellar abundances. If Pd originates from weak r like Sr, [Pd/Ba] must show a correlation with the slope of unity to [Sr/Ba]. If Pd comes from main r like Ba, [Pd/Ba] must be constant. New data show a mild correlation with the slope less than unity, suggesting that the weak r-process fraction for Pd takes intermediate value between those of Sr and Ba 10%. Therefore, this implies that the weak r-process yield decreases gradually from Sr to Ba. 

Two problems were identified with the GCR production, compared to me-teoritic composition the 7Li/6Li ratio ( 2 in GCR but 12 in meteorites) and the nB/10B ratio ( 2.5 in GCR but 4 in meteorites). Modern solutions to those problems involve stellar production of 70% of 7Li (in the hot envelopes of AGB stars and/or novae) and of 40% of nB (through //-induced spallation of 12C in SNII). In both cases, however, uncertainties in the yields are such that observations are used to constrain the yields of the candidate sources rather than to confirm the validity of the scenario. 

Fig. 1. Abundance gradient of N/O predicted by models adopting stellar yields where rotation is not taken into account (as model 7 of [3] - thin solid line) and the same models computed with MM02 yields ([2] - thick solid line). A model where we increased only the amount of primary N in massive stars for metallicities below Z=10-B overlaps with the thick solid line shown here [1], This shows that the N/O gradient along the MW disk is affected mainly by the amount of nitrogen production in low and intermediate mass stars and not the primary N in massive stars. For the abundance data see [3] and references therein - asterisks are B stars (see Cunha, this conference).

We present chemical evolution models for NGC 6822 computed with five fixed parameters, all constrained by observations, and only a free parameter, related with galactic winds. The fixed parameters are i) the infall history that has produced NGC 6822 is derived from its rotation curve and a cosmological model ii) the star formation history of the whole galaxy based on star formation histories for 8 zones inferred from H-R diagrams iii) the IMF, the stellar yields, and the percentage of Type la SNe progenitors are the same than those that reproduce the chemical history of the Solar Vicinity and the Galactic disk. 

Only one or two first stellar generations containing normal stars plus very massive stars included in the best model of PM04, produce negligible effects on the subsequent photo-chemical evolution, when either the yields of HW02 or those of UN are adopted. Therefore, these models are acceptable and we cannot assess Pop III existence nor disproved it. 

Some sample results of calculations of stellar yields, i.e. the mass of a nuclear species freshly synthesized and ejected from a star of given initial mass and chemical composition, are given in Tables 7.2, 7.3 and 7.4. The last column of Table 7.2 gives an IMF-integrated yield which can be compared with the Solar-System abundances. 

After van den Hoek Groenevegen (1997), with their standard parameters, except that for Z = 0.001 the mass loss parameter t) in the Reimers (1975) formula is 1 instead of 4. The lowest block represents the overall yields contributed by intermediate-mass stars in a population governed by a Salpeter mass function between 0.1 and 120 M , calculated from the above stellar yields by Marigo (2001), to be compared with solar abundances (by mass) given in the second line. 

When the stellar yields are only a function of mass and chemical composition, the term ez is given by... 

The predictions of ratios of primary elements formed by massive stars are not specific to the Simple model that model just provides a convenient framework in which to discuss them. The case for other element ratios may be more complicated there is an illuminating discussion by Wheeler, Sneden and Truran (1989) who comprehensively review the older literature, and there is a more recent review by Me William (1997). Regarding the data in Figs. 8.1 and 8.2, all stellar nucleosynthesis models lead one to expect a nearly constant O/Ne ratio, but the O/S ratio could conceivably vary because sulphur is more affected by explosive (as opposed to hydrostatic) nucleosynthesis with a yield per star that is estimated not to increase greatly with the star s initial mass (Table 7.2 and references therein). Figure 8.2 provides little evidence for any variation in practice. 

Fig. 11.13. Left panel projected heavy-element abundance Zp along lines of sight as a function of galactocentric distance, for differing values of the mass fraction in the form of stars at the onset of a terminal galactic wind. Right panel (mass-weighted) mean abundance as a function of final total stellar mass, for two different assumptions as to the dependence of the amount of gas lost on the initial mass. The assumed bulk yield is 0.02 and the trend along the linear part of the curves is approximately Z a M3/8. Adapted from Larson (1974b).

Fig. 11.17. Metallicities of stars and gas as a function of the total mass of stars in an elliptical galaxy growing by mergers, assuming a true yield of 0.02. The trend is for stellar Z to increase approximately as A/1/2 for small masses, flattening to Af1/4 for larger ones. Filled circles show the point beyond which there will be little star formation in mergers because the gas cannot cool sufficiently between collisions arrows indicate possible outcomes of further mergers without star formation. After Tinsley and Larson (1979).

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