相关论文: The Temperature Structure in Ionized Nebulae and t…
In this review we present a brief discussion on the observational evidence in favor of the presence of temperature variations, and conclude that many planetary nebulae show spatial temperature variations that are larger than those predicted…
In this summary I review some results relative to: planetary nebulae, H II regions, chemical evolution of galaxies, and the determination of the primordial helium abundance. These results were presented during the symposium "Ionized Gaseous…
Chemical abundances provide important clues to the evolution of galaxies. Ionized nebulae are one of the main sources of chemical abundance measurements, especially in external galaxies. Studies of H II regions have shown that the overall…
We discuss the role of the electron temperature in abundance determinations in ionized nebulae (planetary nebulae and giant HII regions). We show that, even when observations provide a direct estimate of Te, abundance determinations may…
A review of some of the papers that discuss the relevance of the temperature structure present in H II regions and planetary nebulae is presented. Particular attention is given to the determination of the chemical abundances of these…
It is argued that an important fraction of PNe present large temperature variations that are not due to observational errors nor to incomplete atomic physics. Seven possible causes for these variations are reviewed, one of them is presented…
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…
Electron temperatures, densities, ionic and elemental abundances of helium, nitrogen, oxygen, argon, sulfur and neon were derived for a sample of bulge planetary nebulae, representative of its intermediate mass population. Using these…
Estimates of the gas temperature in planetary nebulae obtained from the [O III] emission line ratio and from the Balmer discontinuity indicate differences reaching up to 6000 K (Liu and Danziger 1993). The [O III] temperature is commonly…
A present prevailing open problem planetary nebulae research, and photoionized gaseous nebulae research at large, is the systematic discrepancies in ionic abundances derived from recombination and collisionally excited lines in many H II…
In this tutorial it is explained the procedure to analyze an optical emission-line spectrum produced by a nebula ionized by massive star formation. Particularly, it is described the methodology used to derive physical properties, such as…
We have constructed photo-ionization models of five galactic bulge planetary nebulae using our automatic method which enables a fully self-consistent determination of the physical parameters of a planetary nebula. The models are constrained…
A prevailing open problem in planetary nebulae research, and photoionized gaseous nebulae research at large, is the systematic discrepancies in electron temperatures and ionic abundances as derived from recombination and collisionally…
The study of the chemical composition of Planetary Nebulae in external galaxies is of paramount importance in the fields of stellar evolution and of the chemical enrichment history of galaxies. In the last years a number of spectroscopic…
The role of planetary nebulae as probes for the galactic chemical evolution is reviewed. Their abundances throughout the Galaxy are discussed for key elements, in particular oxygen and other alpha elements. The abundance distribution…
The determination of chemical abundances in star-forming galaxies and the study of their evolution on cosmological timescales are powerful tools for understanding galaxy formation and evolution. This contribution presents the latest results…
HII regions, ionized nebulae where massive star formation has taken place, exhibit a wealth of emission lines that are the fundamental basis for estimating the chemical composition of the Universe. For more than 80 years, a discrepancy of…
Ionized nebulae are key to understanding the chemical composition and evolution of the Universe. Among these nebulae, H~{\sc ii} regions and planetary nebulae are particularly important as they provide insights into the present and past…
The magnitude of the temperature fluctuations (t^2) required to explain the observed inconsistencies between metallicities inferred from recombination lines and from forbidden lines cannot be attained by steady-state equilibrium…
Since stellar populations enhance particular element abundances according to the yields and lifetimes of the stellar progenitors, the chemical evolution of galaxies serves as one of the key tools that allows the tracing of galaxy evolution.…