Planetary nebulas

Planetary atmospheres Planetary geology Planetary nebulae Planetary ring systems... 

Key words M 2-9 - AFGL 2688 - Nebulae Planetary - Infrared Spectra... 

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]... 

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. 

Planetary nebulae (PNe) offer the opportunities 1) to study stellar nucleosynthesis in the advanced phases of stellar evolution of stars in the wide mass range - -O. S to Mq and 2) to probe radial and as well horizontal/vertical chemical gradients in spiral galaxies by the time of formation of their progenitors. 

Abstract. We discuss new observations of 3He towards planetary nebulae (PNe) using the Very Large Array (VLA), the 305 m Arecibo telescope, which is now capable of observing the 3He+ spectral transition, and the recently commissioned 100 m Green Bank Telescope (GBT). 

Fig. 1. Interstellar 3He/H abundances as a function of source metallicity [2], The [3He/H] abundances by number derived for the H n region sample are given with respect to the solar ratio. Also shown is the abundance derived for the planetary nebula NGC3242 (triangle). We note that there is no trend in the 3He/H abundance with source metallicity...

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

For completeness, we would like to mention the recent work on bulge planetary nebulae by Corny et al. (2004) and Exter et al. (2004), that found an oxygen excess of 0.2dex in bulge planetary nebulae relative to disk ones. 

Hu region abundances in gas-rich dwarfs. Richer, McCall, Stasinska (1998) compared dlrr H n region O abundances with O abundances of planetary nebulae (PNe) in dSphs. While the offset persisted, PNe have only been detected in the two most luminous dSphs and trace primarily intermediate-age populations as opposed to the present-day abundances in Hu regions. 

Radioastronomers first learned of 3He in 1955 at the fourth I.A.U. Symposium in Jodrell Bank, when the frequency of the hyperfine 3He+ line at 8.666 GHz (3.46 cm) was included by Charles Townes in a list of radio-frequency lines of interest to astronomy (Townes 1957). The line was (probably) detected for the first time only twenty years later, by Rood, Wilson Steigman (1979) in W51, opening the way to the determination of the 3He abundance in the interstellar gas of our Galaxy via direct (although technically challenging) radioastronomical observations. In the last two decades, a considerable collection of 3He+ abundance determinations has been assembled in Hi I regions and planetary nebulae. The relevance of these results will be discussed in Sect. 4 and 5 respectively. 

The most direct, model independent, way to test the validity of the mixing solution is to measure the 3He abundance in the ejecta of low-mass stars, i.e. in planetary nebulae (PNe). The search for 3He in the ejecta of PNe via the 8.667 GHz spin-flip transition of 3He+, painstakingly carried out by Rood and coworkers at the Green Bank radiotelescope since 1992 (see summary of results in Balser et al. 1997), has produced so far one solid detection (NGC 3242, see Rood, Bania, Wilson 1992 confirmed with the Effelsberg radiotelescope by... 

Fig. 2. GBT Composite Spectrum of Planetary Nebulae. This 125.7 receiver hour integration is the spectral average of 4 PNe NGC3242 + NGC6543 + NGC6826 + NGC 7009. Shown are the Gaussian fits to the H171 r left) and 3He+ (right) transitions...

L. Stanghellini, J.R. Walsh, N.G. Douglas (Eds.) Planetary Nebulae Beyond the Milky Way... 

Low (<1 solar mass) Middle (5-10 solar masses) High (>20 solar masses) Protostar — pre-main sequence — main sequence — red giant — planetary nebula — white dwarf — black dwarf Protostar - main sequence — red giant — planetary nebula or supernova —> white dwarf or neutron star Protostar — main sequence —> supergiant — supernova — neutron star... 

The birth of a protostar and its life as a pre-main-sequence star, its descent to the main sequence and death, starting with a red giant leading to planetary nebula and ending in white and black dwarfs. This sequence varies with mass... 

Figure 5.15 IR spectrum of the compact planetary nebula. (Reproduced by courtesy of Scott Sandford, NASA Ames Research Center)...

Planetary nebula A cloud of glowing, ionised gas ejected by a star as it begins to die. 

Middle-sized stars, between about 1 and 8 M , undergo complicated mixing processes and mass loss in advanced stages of evolution, culminating in the ejection of a planetary nebula while the core becomes a white dwarf. Such stars are important sources of fresh carbon, nitrogen and heavy elements formed by the slow neutron capture (s-) process (see Chapter 6). Finally, small stars below 1 M have lifetimes comparable to the age of the Universe and contribute little to chemical enrichment or gas recycling and merely serve to lock up material. 

In gas clouds containing one or more hot stars (7 cn > 30 000 K), hydrogen atoms are ionized by the stellar UV radiation in the Lyman continuum and recombine to excited levels their decay gives rise to observable emission lines such as the Balmer series (see, for example, Fig. 3.22). Examples are planetary nebulae (PN), which are envelopes of evolved intermediate-mass stars in process of ejection and... 

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. 

Planetary nebulae (PN) display basic abundance patterns characteristic of the age and location of their parent stellar populations, on which are superimposed the effects of evolution through giant, AGB and post-AGB stages of their own central... 

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.

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