Supernovae

The astrochemistty of ions may be divided into topics of interstellar clouds, stellar atmospheres, planetary atmospheres and comets. There are many areas of astrophysics (stars, planetary nebulae, novae, supemovae) where highly ionized species are important, but beyond the scope of ion chemistry . (Still, molecules, including H2O, are observed in solar spectra [155] and a surprise in the study of Supernova 1987A was the identification of molecular species, CO, SiO and possibly ITf[156. 157]. ) In the early universe, after expansion had cooled matter to the point that molecules could fonn, the small fraction of positive and negative ions that remained was crucial to the fomiation of molecules, for example [156]... 

Sometimes a star explodes in a supernova cast mg debris into interstellar space This debris includes the elements formed during the life of the star and these elements find their way into new stars formed when a cloud of matter collapses in on itself Our own sun is believed to be a second generation star one formed not only from hydrogen and helium but containing the elements formed in earlier stars as well... 

Super milling dyes Supermumetal Supernovas Superoxide dismutase... 

Helium, plentiful in the cosmos, is a product of the nuclear fusion reactions that are the prime source of stellar energy. The other members of the hehum-group gases are thought to have been created like other heavier elements by further nuclear condensation reactions occurring at the extreme temperatures and densities found deep within stars and in supernovas. 

TJ Loredo. In PE Eougere, ed. Erom Laplace to Supernova SN 1987A Bayesian Inference m Astrophysics. Dordrecht, The Netherlands Kluwer, 1990, pp 81-142. 

L. A. Marschall, The Supernova Story, Plenum Press, New York, 1989, 276 pp. P. Murdin, End in Fire The Supernova in the Large Magellanic Cloud, Cambridge University Press, 1990, 253 pp. 

Proton capture processes by heavy nuclei have already been briefly mentioned in several of the preceding sections. The (p,y) reaction can also be invoked to explain the presence of a number of proton-rich isotopes of lower abundance than those of nearby normal and neutron-rich isotopes (Fig. 1.5). Such isotopes would also result from expulsion of a neutron by a y-ray, i.e. (y,n). Such processes may again be associated with supernovae activity on a very short time scale. With the exceptions of " ln and " Sn, all of the 36 isotopes thought to be produced in this way have even atomic mass numbers the lightest is Se... 

Jorgensen CK (1990) Heavy Elements Synthesized in Supernovae and Detected in Peculiar A-type Stars. 73 199-226... 

Before-and-after photos of a supernova that appeared in 1987. The arrow in the left photo indicates the star that exploded. The picture on the right shows the aftermath of the explosion. 

Table 2.2 The pre-supernova burning stages of a star with 25 solar masses. From Macia et al. (1997)...

An unknown event disturbed the equilibrium of the interstellar cloud, and it collapsed. This process may have been caused by shock waves from a supernova explosion, or by a density wave of a spiral arm of the galaxy. The gas molecules and the particles were compressed, and with increasing compression, both temperature and pressure increased. It is possible that the centrifugal forces due to the rotation of the system prevented a spherical contraction. The result was a relatively flat, rotating disc of matter, in the centre of which was the primeval sun. Analogues of the early solar system, i.e., protoplanetary discs, have been identified from the radiation emitted by T Tauri stars (Koerner, 1997). 

The evaporation of volatile components by heat from supernovae or passing stars... 

The question also arises as to where the chiral molecules came from. Were the L-amino acids or the D-sugars selected on the primeval Earth, or are exuaterresuial sources responsible for the homochirality This second possibility is dealt with by hypotheses on the effect of circularly polarised light, of extraterrestrial origin, on chiral molecules in the molecular clouds from which the solar system was formed. One such hypothesis was proposed by Rubenstein et al. (1983) and developed further by others, particularly A. W. Bonner (Bonner and Rubenstein, 1987) both scientists worked at Stanford University. The authors believe that the actual radiation source was synchrotron radiation from supernovae. The excess of one enantiomeric form generated by this irradiation process would have needed to be transported to Earth by comets and meteorites, probably during the bombardment phase around 4.2-3.8 billion years ago. 

The environment must be free from life-threatening supernovae. 

Three sources have been proposed to produce fluorine in the Galaxy. The first was suggested by Forestini et al. (1992) and refers to production in low-mass stars during the AGB phase while two others are related to massive stars production in Wolf-Rayet stars (Meynet Arnould 2000) and in type II Supernovae, via the neutrino-induced nucleosynthesis (Woosley et al. 1990). 

The bulge sample shows enhancements in [a/Fe] at all [Fe/H] values, with the exception of a decreasing trend in [O/Fe] at high [Fe/H], The difference in [O/Fe] and [Mg/Fe] trends creates a quandary Type II models (e.g. [6]) predict that O and Mg are produced in similar mass progenitors. There are no major producers of Mg other than Type II supernovae. Therefore, why do O and Mg not show similar distributions ... 

The derived supernovae ratios of the metal-rich systems in Table 1 indicate that both the low-a and low iron-peak abundances are consistent with significant contributions from Type la supernovae. In general, when compared with the abundances of stars born within the MWG, the metal-rich stars associated with the Sgr dSph possess low iron-peak abundances relative to iron (e.g., [3], [4]). 

By comparing the observed chemical abundance ratios to supernova model yields, one can calculate , the ratio of the number of SNe la to SNe II events that fit the observations and the synthesized mass of the elements from the model yields. In a study adopting the same analysis techniques as those performed here, [5] found large values of for a trio of low-a stars of [Fe/H] -2. Employing the abundances derived in this study of stars with comparable metallicities, I find that the metal-poor systems presented here possess a- and iron-peak abundances (and based on Na, Mg, Si and Fe) consistent with those observed in metal-poor stars of the MWG (e.g., [6]). 

Fig. 3. Depletions of O, A1 and Na suggest enhanced type la supernova contribution.

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