Beschreibung: Galaxies, Vol. 6, Pages 91: Towards the Provision of Accurate Atomic Data for Neutral Iron Galaxies doi: 10.3390/galaxies6030091 Authors: Andrew Conroy Catherine Ramsbottom Connor Ballance Francis Keenan The rich emission and absorption line spectra of Fe I may be used to extract crucial information on astrophysical plasmas, such as stellar metallicities. There is currently a lack, in quality and quantity, of accurate level-resolved effective electron-impact collision strengths and oscillator strengths for radiative transitions. Here, we discuss the challenges in obtaining an accurate model of the neutral iron atom and compare our theoretical fine-structure energy levels with observation for several increasingly large models. Radiative data is presented for several transitions for which the atomic data is accurately known.

Beschreibung: Galaxies, Vol. 6, Pages 90: Benchmarking Current Capabilities for the Generation of Excitation and Photoionisation Atomic Data Galaxies doi: 10.3390/galaxies6030090 Authors: Catherine Ramsbottom Connor Ballance Ryan Smyth Andrew Conroy Luis Fernández-Menchero Michael Turkington Francis Keenan The spectra currently emerging from modern ground- and space-based astronomical instruments are of exceptionally high quality and resolution. To meaningfully analyse these spectra, researchers utilise complex modelling codes to replicate the observations. The main inputs to these codes are atomic data such as excitation and photoionisation cross sections, as well as radiative transition probabilities, energy levels, and line strengths. In this publication, the current capabilities of the numerical methods and computer packages used in the generation of these data are discussed. Particular emphasis is given to Fe-peak species and the heavy systems of tungsten and molybdenum. Some of the results presented to highlight certain issues and/or advances have already been published in the literature, while other sections present new recently evaluated atomic data for the first time.

Beschreibung: Galaxies, Vol. 6, Pages 89: Jsolated Stars of Low Metallicity Galaxies doi: 10.3390/galaxies6030089 Authors: Efrat Sabach We study the effects of a reduced mass-loss rate on the evolution of low metallicity Jsolated stars, following our earlier classification for angular momentum (J) isolated stars. By using the stellar evolution code MESA we study the evolution with different mass-loss rate efficiencies for stars with low metallicities of Z = 0 . 001 and Z = 0 . 004 , and compare with the evolution with solar metallicity, Z = 0 . 02 . We further study the possibility for late asymptomatic giant branch (AGB)—planet interaction and its possible effects on the properties of the planetary nebula (PN). We find for all metallicities that only with a reduced mass-loss rate an interaction with a low mass companion might take place during the AGB phase of the star. The interaction will most likely shape an elliptical PN. The maximum post-AGB luminosities obtained, both for solar metallicity and low metallicities, reach high values corresponding to the enigmatic finding of the PN luminosity function.

Beschreibung: Galaxies, Vol. 6, Pages 88: Revealing the True Nature of Hen 2-428 Galaxies doi: 10.3390/galaxies6030088 Authors: Nicole Reindl Nicolle L. Finch Veronika Schaffenroth Martin A. Barstow Sarah L. Casewell Stephan Geier Marcelo M. Miller Bertolami Stefan Taubenberger The nucleus of Hen 2-428 is a short orbital period (4.2 h) spectroscopic binary, whose status as potential supernovae type Ia progenitor has raised some controversy in the literature. We present preliminary results of a thorough analysis of this interesting system, which combines quantitative non-local thermodynamic (non-LTE) equilibrium spectral modelling, radial velocity analysis, multi-band light curve fitting, and state-of-the art stellar evolutionary calculations. Importantly, we find that the dynamical system mass that is derived by using all available He II lines does not exceed the Chandrasekhar mass limit. Furthermore, the individual masses of the two central stars are too small to lead to an SN Ia in case of a dynamical explosion during the merger process.

Beschreibung: Galaxies, Vol. 6, Pages 87: R-Matrix Scattering Calculations for Iron-Peak Species: Photoionisation of Fe I and Electron-Impact Excitation of Fe II Galaxies doi: 10.3390/galaxies6030087 Authors: Ryan T. Smyth Catherine A. Ramsbottom Connor P. Ballance An abundance of absorption and emission lines of iron-peak species such as Fe I and Fe II can be seen in the spectra of many astrophysical objects. Thus, the accurate modelling of such spectra requires sets of high quality atomic data for these species. In this paper, we present preliminary results from the present electron-impact excitation calculations for Fe II and fine-structure resolved photoionisation calculations for Fe I employing the Dirac atomic R-matrix and Breit–Pauli R-matrix methods. For the Fe II excitation, we compare results with all existing calculations, and for the Fe I photoionisation, we present a sample of level-resolved cross-sections. The calculations and results described throughout will be of use to those requiring high quality atomic data for modelling a wide variety of astrophysical objects.

Beschreibung: Galaxies, Vol. 6, Pages 86: Molecular Data Needs for Modelling AGB Stellar Winds and Other Molecular Environments Galaxies doi: 10.3390/galaxies6030086 Authors: Taïssa Danilovich Leen Decin Marie Van de Sande The modern era of highly sensitive telescopes is enabling the detection of more and more molecular species in various astronomical environments. Many of these are now being carefully examined for the first time. However, to move beyond detection to more detailed analysis such as radiative transfer modelling, certain molecular properties need to be properly measured and calculated. The importance of contributions from vibrationally excited states or collisional (de-)excitations can vary greatly, depending on the specific molecule and the environment being studied. Here, we discuss the present molecular data needs for detailed radiative transfer modelling of observations of molecular rotational transitions, primarily in the (sub-)millimetre and adjacent regimes, and with a focus on the stellar winds of AGB stars.

Beschreibung: Galaxies, Vol. 6, Pages 85: Surveying Planetary Nebulae Central Stars for Close Binaries: Constraining Evolution of Central Stars Based on Binary Parameters Galaxies doi: 10.3390/galaxies6030085 Authors: Todd Hillwig The increase in discovered close binary central stars of planetary nebulae is leading to a sufficiently large sample to begin to make broader conclusions about the effect of close binary stars on common envelope evolution and planetary nebula formation. Herein I review some of the recent results and conclusions specifically relating close binary central stars to nebular shaping, common envelope evolution off the red giant branch, and the total binary fraction and double degenerate fraction of central stars. Finally, I use parameters of known binary central stars to explore the relationship between the proto-planetary nebula and planetary nebula stages, demonstrating that the known proto-planetary nebulae are not the precursors of planetary nebulae with close binary central stars.

Beschreibung: Galaxies, Vol. 6, Pages 84: Analysis of Multiple Shell Planetary Nebulae Based on HST/WFPC2 Extended 2D Diagnostic Diagrams Galaxies doi: 10.3390/galaxies6030084 Authors: Daniela Barría Stefan Kimeswenger The investigation of gaseous nebulae, emitting in forbidden lines, is often based extensively on diagnostic diagrams. The special physics of these lines often allows for disentangling with a few line ratios normally coupled thermodynamic parameters like electron temperature, density and properties of the photo-ionizing radiation field. Diagnostic diagrams are usually used for the investigation of planetary nebulae as a total. We investigated the extension of such integrated properties towards spatially resolved 2D diagnostics, using Hubble Space Telescope/Wide Field Planetary Camera 2 (HST/WFPC2) narrow band images. For this purpose, we also derived a method to isolate pure Hα emission from the [N ii] contamination as normally suffering in the F656N HST/WFPC2 filter.

Beschreibung: Galaxies, Vol. 6, Pages 83: Applications of a Particular Four-Dimensional Projective Geometry to Galactic Dynamics Galaxies doi: 10.3390/galaxies6030083 Authors: Jacques L. Rubin Relativistic location systems that extend relativistic positioning systems show that pseudo-Riemannian space-time geometry is somehow encompassed in a particular four-dimensional projective geometry. The resulting geometric structure is then that of a generalized Cartan space (also called Cartan connection space) with projective connection. The result is that locally non-linear actions of projective groups via homographies systematically induce the existence of a particular space-time foliation independent of any space-time dynamics or solutions of Einstein’s equations for example. In this article, we present the consequences of these projective group actions and this foliation. In particular, it is shown that the particular geometric structure due to this foliation is similar from a certain point of view to that of a black hole but not necessarily based on the existence of singularities. We also present a modified Newton’s laws invariant with respect to the homographic transformations induced by this projective geometry. Consequences on galactic dynamics are discussed and fits of galactic rotational velocity curves based on these modifications which are independent of any Modified Newtonian Dynamics (MOND) or dark matter theories are presented.

Beschreibung: Galaxies, Vol. 6, Pages 82: Simulations and Modeling of Intermediate Luminosity Optical Transients and Supernova Impostors Galaxies doi: 10.3390/galaxies6030082 Authors: Amit Kashi More luminous than classical novae, but less luminous than supernovae, lies the exotic stellar eruptions known as Intermediate luminosity optical transients (ILOTs). They are divided into a number of sub-groups depending on the erupting progenitor and the properties of the eruption. A large part of the ILOTs is positioned on the slanted Optical Transient Stripe (OTS) in the Energy-Time Diagram (ETD) that shows their total energy vs. duration of their eruption. We describe the different kinds of ILOTs that populate the OTS and other parts of the ETD. The high energy part of the OTS hosts the supernova impostors—giant eruptions (GE) of very massive stars. We show the results of the 3D hydrodynamical simulations of GEs that expose the mechanism behind these GEs and present new models for recent ILOTs. We discuss the connection between different kinds of ILOTs and suggest that they have a common energy source—gravitational energy released by mass transfer. We emphasize similarities between Planetary Nebulae (PNe) and ILOTs, and suggest that some PNe were formed in an ILOT event. Therefore, simulations used for GEs can be adapted for PNe, and used to learn about the influence of the ILOT events on the central star of the planetary nebula.