Related papers: Temperature Variations and Abundance Determination…
We have carried out a new photometric V,Rc study of 12 protoplanetary nebulae, objects in the short-lived transition between the AGB and PN phases of stellar evolution. These had been the subjects of an earlier study, using data from…
We analyse a large sample of galactic planetary nebulae based on their chemical composition and morphology. A recent morphological classification system is adopted, and several elements are considered, namely He, N, O, S, Ar, Ne, and C in…
Radial abundance gradients are a common feature of spiral galaxies, and in the case of the Galaxy both the magnitude of the gradients and their variations are among the most important constraints of chemical evolution models. Planetary…
How good is our universe at making habitable planets? The answer to this depends on which factors are important for life: Does a planet need to be Earth mass? Does it need to be inside the temperate zone? are systems with hot Jupiters…
A review of the abundances and condensation temperatures of the elements and their nuclides in the solar nebula and in chondritic meteorites. Abundances of the elements in some neighboring stars are also discussed.
Planetary nebulae (PNe) provide tests of stellar evolution, can serve as tracers of chemical evolution in the Milky Way and other galaxies, and are also used as a calibrator of the cosmological distance ladder. Current and upcoming large…
We have studied the time variation of the radial abundance gradients using samples of planetary nebulae, open clusters, cepheids and other young objects. Based on the analysis of O/H and S/H abundances for planetary nebulae and…
NASA's Cosmic Background Explorer (COBE) Satellite has recently made the most accurate measurement of the temperature of the Universe determining it to be $2.726\pm 0.01\,$K. In trying to understand why the temperature has this value, one…
The measurement of chemical abundances in planetary nebulae in nearby galaxies is now relatively straightforward. The challenge is to use these chemical abundances to infer the chemical evolution of their host galaxies. At this point, our…
We illustrate how rotation of the central star can give rise to latitudinal variations in the wind properties from the star. Interaction of these winds with the surrounding medium can produce asymmetrical planetary nebulae.
Many planetary nebulae (PNe) exhibit distinctly non-axisymmetric structure in either (i) the shape of the nebula, or (ii) in the off-centered position of the illuminating star. By examining a large number of well resolved images of PNe we…
Having completed my search for faint PNe in the LMC, including the outer 64 deg2 area not covered in the original UKST survey, I now have the most complete number of PNe within any galaxy with which to assess stellar parameters. I present…
This paper looks into various aspects brought to light by numerical work on the generalized interacting winds model for planetary nebulae. First, a detailed comparison between radiative and non-radiative models is made, showing that one's…
There is evidence for temperature fluctuations in Planetary Nebulae and in Galactic HII regions. If such fluctuations occur in the low-metallicity, extragalactic HII regions used to probe the primordial helium abundance, the derived 4He…
The possibility of the phenomenon of Bose condensation having a part to play in the discussion of neutron stars has been around for some time. Here the sorts of temperatures and densities that might be involved are discussed. Also, an…
The well-known formal analogy between time and absolute temperature, existing on the quantum level, is considered as a profound duality relationship requiring some modifications in the conventional quantum dynamics. They consist of tiny…
Aims. The main objective of this article is to provide a simple physical framework with permits a quantitative comparison of measurements of the temperature fluctuations in the ionized interstellar medium with possible mechanisms which can…
From an extended relativistic dynamics for a particle moving in a cosmic background field with temperature T, we aim to obtain the speed of light with an explicit dependence on the background temperature of the universe. Although finding…
The effect of the nebula optical depth on the determination of the temperature (T*) of the central stars in planetary nebulae is discussed. Based on photoionization models for planetary nebulae with different optical depths, we show,…
We review the evolution of our understanding of the planetary nebulae phenomenon and their place in the scheme of stellar evolution. The historical steps leading to our current understanding of central star evolution and nebular formation…