Related papers: Can solid body destruction explain abundance discr…
Evolution of large-scale scalar perturbations in the presence of stiff solid (solid with pressure to energy density ratio > 1/3) is studied. If the solid dominated the dynamics of the universe long enough, the perturbations could end up…
Bipolar planetary nebulae (PNe), as well as extreme elliptical PNe are formed through the influence of a stellar companion. But half of all PN progenitors are not influenced by any stellar companion, and, as I show here, are expected to…
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…
Our understanding of the chemical evolution of the Galactic bulge requires the determination of abundances in large samples of giant stars and planetary nebulae (PNe). We discuss PNe abundances in the Galactic bulge and compare these…
The observed rapid onset of star formation in molecular clouds requires rapid formation of dense fragments which can collapse individually before being overtaken by global gravitationally-driven flows. Many previous investigations have…
Recent spectroscopic observations of planetary nebulae (PNe) in several elliptical galaxies have revealed structural and kinematical properties of the outer stellar halo regions. In order to elucidate the origin of the properties of these…
As mass-losing asymptotic giant branch (AGB) stars evolve to planetary nebulae (PNe), the mass outflow geometries transform from nearly spherical to extreme aspherical. The physical mechanisms governing this transformation are widely…
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…
The morphology of planetary nebulae emerging from the common envelope phase of binary star evolution is investigated. Using initial conditions based on the numerical results of hydrodynamical simulations of the common envelope phase it is…
The plethora of asymmetric planetary nebulae and the curiously high momenta of pre-planetary nebula outflows suggest that rotational energy is extracted from the engines. Magneto-rotational outflows driven by dynamos might be operating…
We present values for angular diameter, flux and extinction for 70 Galactic planetary nebulae observed using narrow band filters. Angular diameters are derived using constant emissivity shell and photoionization line emission models. The…
Planetary nebulae (PNe) constitute an important tool to study the chemical evolution of the Milky Way and other galaxies, probing the nucleosynthesis processes, abundance gradients and the chemical enrichment of the interstellar medium. In…
Most stars form in compact, dense embedded clusters with memberships ranging from a dozen stars to many millions of stars. Embedded clusters containing more than a few hundred stars also contain O stars that disrupt the nebula abruptly.…
In this paper, we will focus on the advances made in the last few years regarding the abundance discrepancy problem in ionized nebulae. We will show the importance of collecting deep, high-quality data of H II regions and planetary nebulae…
Observations and models of giant planets indicate that such objects are enriched in heavy elements compared to solar abundances. The prevailing view is that giant planets accreted multiple Earth masses of heavy elements after the end of…
We study the density structures of planetary nebulae implied by four diagnostics that sample different regions within the nebulae: [S II] $\lambda6716/\lambda6731$, [O II] $\lambda3726/\lambda3729$, [Cl III] $\lambda5518/\lambda5538$, and…
We analyze the mass distribution of stellar black holes derived from the light and radial velocity curves of optical stars in close binary systems using dynamical methods. The systematic errors inherent in this approach are discussed. These…
The hot Saturn population exhibits a boundary in mass-radius space, such that no planets are observed at a density less than $\sim$0.1 g cm$^{-3}$. Yet, planet interior structure models can readily construct such objects as the natural…
We previously determined abundances of He, C, N, O, and Ne for a sample of planetary nebulae (PNe) representing a broad range in progenitor mass and metallicity, and we now compare them with theoretical predictions of PNe abundances from a…
The comparison of chemical abundances in the neutral gas of galaxies to photospheric abundances of old and young stars, ionized gas abundances, and abundances in galactic halos can trace the chemical enrichment of the universe through…