Description: Galaxies, Vol. 6, Pages 101: The Formation of Fullerenes in Planetary Nebulae Galaxies doi: 10.3390/galaxies6040101 Authors: Jan Cami Els Peeters Jeronimo Bernard-Salas Greg Doppmann James De Buizer In the last decade, fullerenes have been detected in a variety of astrophysical environments, with the majority being found in planetary nebulae. Laboratory experiments have provided us with insights into the conditions and pathways that can lead to fullerene formation, but it is not clear precisely what led to the formation of astrophysical fullerenes in planetary nebulae. We review some of the available evidence, and propose a mechanism where fullerene formation in planetary nebulae is the result of a two-step process where carbonaceous dust is first formed under unusual conditions; then, the fullerenes form when this dust is being destroyed.

Description: Galaxies, Vol. 6, Pages 100: Challenges and Techniques for Simulating Line Emission Galaxies doi: 10.3390/galaxies6040100 Authors: Karen P. Olsen Andrea Pallottini Aida Wofford Marios Chatzikos Mitchell Revalski Francisco Guzmán Gergö Popping Enrique Vázquez-Semadeni Georgios E. Magdis Mark L. A. Richardson Michaela Hirschmann William J. Gray Modeling emission lines from the millimeter to the UV and producing synthetic spectra is crucial for a good understanding of observations, yet it is an art filled with hazards. This is the proceedings of “Walking the Line”, a 3-day conference held in 2018 that brought together scientists working on different aspects of emission line simulations, in order to share knowledge and discuss the methodology. Emission lines across the spectrum from the millimeter to the UV were discussed, with most of the focus on the interstellar medium, but also some topics on the circumgalactic medium. The most important quality of a useful model is a good synergy with observations and experiments. Challenges in simulating line emission are identified, some of which are already being worked upon, and others that must be addressed in the future for models to agree with observations. Recent advances in several areas aiming at achieving that synergy are summarized here, from micro-physical to galactic and circum-galactic scale.

Description: Galaxies, Vol. 6, Pages 99: AGBs, Post-AGBs and the Shaping of Planetary Nebulae Galaxies doi: 10.3390/galaxies6030099 Authors: Eric Lagadec During the last decades, observations, mostly with the Hubble Space Telescope, have revealed that round Planetary Nebulae were the exception rather than rule. A huge variety of features are observed, such as jets, discs, tori, showing that the ejection of material is not due to isotropic radiation pressure on a spherical shell and that more physics is involved. This shaping process certainly occur early in the evolution of these low and intermediate mass stars and must leave imprints in the evolutionary stages prior the PN phase. Thanks to news instruments on the most advanced telescopes (e.g., the VLTI, SPHERE/VLT and ALMA), high angular resolution observations are revolutionising our view of the ejection of gas and dust during the AGB and post-AGB phases. In this review I will present the newest results concerning the mass loss from AGB stars, post-AGB stars and related objects.

Description: Galaxies, Vol. 6, Pages 98: X-ray Shaping of Planetary Nebulae Galaxies doi: 10.3390/galaxies6030098 Authors: Martín A. Guerrero The stellar winds of the central stars of planetary nebulae play an essential role in the shaping of planetary nebulae. In the interacting stellar winds model, the fast stellar wind injects energy and momentum, which are transferred to the nebular envelope through an X-ray-emitting hot bubble. Together with other physical processes, such as the ionization of the nebular envelope, the asymmetrical mass-loss in the asymptotic giant branch (AGB), and the action of collimated outflows and magnetic fields, the pressurized hot gas determines the expansion and evolution of planetary nebulae. Chandra and XMM-Newton have provided us with detailed information of this hot gas. Here in this talk I will review our current understanding of the effects of the fast stellar wind in the shaping and evolution of planetary nebulae and give some hints of the promising future of this research.

Description: Galaxies, Vol. 6, Pages 97: Post-AGB Discs from Common-Envelope Evolution Galaxies doi: 10.3390/galaxies6030097 Authors: Robert G. Izzard Adam S. Jermyn Post-asymptotic giant branch (post-AGB) stars with discs are all binaries. Many of these binaries have orbital periods between 100 and 1000 days so cannot have avoided mass transfer between the AGB star and its companion, likely through a common-envelope type interaction. We report on preliminary results of our project to model circumbinary discs around post-AGB stars using our binary population synthesis code binary_c. We combine a simple analytic thin-disc model with binary stellar evolution to estimate the impact of the disc on the binary, and vice versa, fast enough that we can model stellar population and hence explore the rather uncertain parameter space involved with disc formation. We find that, provided the discs form with sufficient mass and angular momentum, and have an inner edge that is relatively close to the binary, they can both prolong the life of their parent post-AGB star and pump the eccentricity of orbits of their inner binaries.

Description: Galaxies, Vol. 6, Pages 96: The Morphology of the Outflow in the Grazing Envelope Evolution Galaxies doi: 10.3390/galaxies6030096 Authors: Sagiv Shiber We study the grazing envelope evolution (GEE), where a secondary star, which orbits the surface of a giant star, accretes mass from the giant envelope and launches jets. We conduct simulations of the GEE with different half-opening angles and velocities, and simulate the onset phase and the spiralling-in phase. We discuss the resulting envelope structure and the outflow geometry. We find in the simulations of the onset phase with narrow jets that a large fraction of the ejected mass outflows along the polar directions. The mass ejected at these directions has the fastest velocity and the highest angular momentum magnitude. In the simulations of the spiralling-in phase, a large fraction of the ejected mass concentrates around the orbital plane. According to our findings, the outflow with the highest velocity is closer to the poles as we launch narrower jets. The outflow has a toroidal shape accompanied by two faster rings, one ring at each side of the equatorial plane. The interaction of the jets with the giant envelope causes these outflow structures, as we do not include in our simulations the secondary star gravity and the envelope self-gravity.

Description: Galaxies, Vol. 6, Pages 95: SpArcFiRe: Enhancing Spiral Galaxy Recognition Using Arm Analysis and Random Forests Galaxies doi: 10.3390/galaxies6030095 Authors: Pedro Silva Leon T. Cao Wayne B. Hayes Automated quantification of galaxy morphology is necessary because the size of upcoming sky surveys will overwhelm human volunteers. Existing classification schemes are inadequate because (a) their uncertainty increases near the boundary of classes and astronomers need more control over these uncertainties; (b) galaxy morphology is continuous rather than discrete; and (c) sometimes we need to know not only the type of an object, but whether a particular image of the object exhibits visible structure. We propose that regression is better suited to these tasks than classification, and focus specifically on determining the extent to which an image of a spiral galaxy exhibits visible spiral structure. We use the human vote distributions from Galaxy Zoo 1 (GZ1) to train a random forest of decision trees to reproduce the fraction of GZ1 humans who vote for the “Spiral” class. We prefer the random forest model over other black box models like neural networks because it allows us to trace post hoc the precise reasoning behind the regression of each image. Finally, we demonstrate that using features from SpArcFiRe—a code designed to isolate and quantify arm structure in spiral galaxies—improves regression results over and above using traditional features alone, across a sample of 470,000 galaxies from the Sloan Digital Sky Survey.

Description: Galaxies, Vol. 6, Pages 94: ALMA’s Acute View of pPNe: Through the Magnifying Glass... and What We Found There Galaxies doi: 10.3390/galaxies6030094 Authors: Carmen Sánchez Contreras Javier Alcolea Valentín Bujarrabal Arancha Castro-Carrizo We present recent Atacama Large Millimeter/submillimeter Array (ALMA)-based studies of circumstellar envelopes (CSEs) around Asymptotic Giant Branch (AGB) stars and pre-Planetary Nebulae (pPNe). In only a few years of operation, ALMA is revolutionising the field of AGB-to-PN research by providing unprecedentedly detailed information on the complex nebular architecture (at large but also on small scales down to a few ∼10 AU from the centre), dynamics and chemistry of the outflows/envelopes of low-to-intermediate mass stars in their late stages of the evolution. Here, we focus on continuum and molecular line mapping studies with high angular resolution and sensitivity of some objects that are key to understanding the complex PN-shaping process. In particular, we offer (i) a brief summary of ALMA observations of rotating disks in post-AGB objects and (ii) report on ALMA observations of OH 231.8+4.2 providing the most detailed and accurate description of the global nebular structure and kinematics of this iconic object to date.

Description: Galaxies, Vol. 6, Pages 93: VALD: The Meeting Point of Data Producers and Data Users Galaxies doi: 10.3390/galaxies6030093 Authors: Tatiana Ryabchikova Yury Pakhomov Nikolai Piskunov Vienna Atomic Line Database (VALD) contains data on atomic and molecular energy levels and parameters of spectral lines required for stellar spectra analysis. Hundreds of millions of lines for fine spectral synthesis and for opacity calculations are collected in the present version of VALD (VALD3). Critical evaluation of the data and the diversity of extraction tools support the high popularity of VALD among users. The data model of VALD3 incorporates obligatory links to the bibliography making our database more attractive as a publishing platform for data producers. The VALD data quality and completeness are constantly improving allowing better reproduction of stellar spectra. To illustrate continuous evolution of the data content we present a comparative analysis of the recent experimental and theoretical atomic data for Fe-group elements, which will be included in the next VALD release. This release will also include a possibility for extracting the line data with full isotopic and hyperfine structures.

Description: Galaxies, Vol. 6, Pages 92: Relieving Tensions Related to the Dark Matter Interpretation of the Fermi-LAT Data Galaxies doi: 10.3390/galaxies6030092 Authors: Man Ho Chan Recently, many studies indicate that the GeV gamma ray excess signal from the central Milky Way can be best explained by ∼40–50 GeV dark matter annihilating via the b b ¯ channel. However, this model appears to be disfavored by the recent Fermi-LAT data for dwarf spheroidal galaxies and the constraint from synchrotron radiation. In this article, we describe a consistent picture to relieve the tensions between the dark matter annihilation model and the observations. We show that a baryonic feedback process is the key to alleviate the tensions and the ∼40–50 GeV dark matter model is still the best one to account for the GeV gamma ray excess in the Milky Way.