Nebula Galactic

Below we will see that meteorites, smaller rocks from asteroidal objects delivered to Earth, provide important information for solar system abundances of non-volatile elements. Other sources to refine solar system abundances are analysis of other solar system objects such as the gas-giant planets, comets and the interplanetary dust particles from comets. Outside the solar system, the compositions of hot B stars, planetary nebulae, Galactic cosmic rays (GCR), the nearby interstellar medium (ISM) and H II regions have been employed to amend the solar system abundances of some elements. 

Abstract. We present recent advances in the determination of chemical abundances of galactic Planetary Nebulae and discuss implications resulting from the comparison with theoretical predictions. From the analysis of diagrams of abundances of N/O vs He/H, N/O vs N/H and N/O vs O/H we argue that very likely the often used solar photospheric abundance of oxygen of 8.9, in usual units, is overestimated by a factor of 2-3, as suggested by very recent work in the Sun. This would solve an astrophysical problem with the measured abundances in planetaries. 

Abundance Variations in the Galactic Disk Planetary Nebulae, Open Clusters and Field Stars... 

Fig. 3.40. Abundances in Galactic stars, H n regions and planetary nebulae, as a function of Galactocentric distance, with the Sun shown for comparison. After Hou, Prantzos and Boissier (2000). The curves show a model calculation by the authors nitrogen is underproduced in the model because only massive stars were considered. 

D. E. Osterbrock and G. J. Ferland, Astrophysics of Gaseous Nebulae and Active Galactic Nuclei, University Science Books, Mill Valley, Cal., 2006, is another classic text, indispensable for studies of emission nebulae. 

Fig. 4.7. 3He/H in simple Galactic H n regions, i.e. those thought to be reasonably well represented by homogeneous spherical models (Balser et al. 1999), and one planetary nebula, as a function of their oxygen abundance. 3He/H is plotted on a logarithmic scale relative to the proto-solar value of 1.5 x 10-5. After Bania, Rood and Balser (2002). Reprinted by permission from Macmillan Publishers Ltd. Courtesy Tom Bania.

Busfield A, Gilmour JD, Whitby JA, Turner G (2004) Iodine-xenon analysis of ordinary chondrite halide implications for early solar system water. Geochim Cosmochim Acta 68 195-202 Busso M, Gallino R, Wasserburg GJ (1999) Nucleosynthesis in asymptotic giant branch stars relevance for galactic enrichment and solar system formation. Annu Rev Astronom Astrophys 37 239-309 Cameron AGW (1969) Physical conditions in the primitive solar nebula. In Meteorite Research. Millman PM (ed) Reidel, Dordrecht, p 7-12... 

The brightest X-ray nebulas are the remnants of supernova explosions. The ejecta are thrown out so forcefully that the collision with neighbouring interstellar gases produces temperatures of several million degrees. This is sufficient to emit photons in the keV range. It is no surprise that most X-ray binaries and supernova remnants should be located in the galactic disk. 

On the profit side of the account, we must record the gas rejected by each dying star, be it supernova or planetary nebula, and reinjected into the great galactic cycle. 

CHEMICAL AND EXPANSION PROPERTIES OF COMPACT PLANETARY NEBULAE IN THE GALACTIC ANTI-CENTER REGION... 

Y. Nakada, H. Izumiura, T. Onaka, 0. Hashimoto, N. Ukiia, S. Deguchi, and T. Tanabe 53 Chemical and Expansion Properties of Compact Planetary Nebulae in the Galactic Anti-Center Region... 

As much as 2 to 5% of the interstellar silicate grain population could be crystalline, yet still lie below our current limits of detection (Li Draine 2001 Kemper et al. 2005). As said before, it could equally well be true that any crystalline silicates injected into the interstellar medium become amorphous after long exposure to galactic cosmic rays. Finally, studies on the spectral evolution of silicate grains in protoplanetary disks indicate that the degree of crystallinity is not simply correlated with age (see Chapter 8 for more details). These observations, argue that processes within the protostellar nebula itself are responsible for the production of crystalline silicates. 

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