7.4 Today´s new entry:
Modelling the 3D physical structure of astrophysical sources with GASS
David Quénard, Sandrine Bottinelli, Emmanuel Caux
Abstract: The era of interferometric observations leads to the need of a more and more precise description of physical structures and dynamics of star-forming regions, from pre-stellar cores to protoplanetary discs. The molecular emission can be traced in multiple physical components such as infalling envelopes, outflows and protoplanetary discs. To compare with the observations, a precise and complex radiative transfer modelling of these regions is needed. We present GASS (Generator of Astrophysical Sources Structure), a code that allows us to generate the three-dimensional (3D) physical structure model of astrophysical sources. From the GASS graphical interface, the user easily creates different components such as spherical envelopes, outflows and discs. The physical properties of these components are modelled thanks to dedicated graphical interfaces that display various figures in order to help the user and facilitate the modelling task. For each component, the code randomly generates points in a 3D grid with a sample probability weighted by the molecular density. The created models can be used as the physical structure input for 3D radiative transfer codes to predict the molecular line or continuum emission. An analysis of the output hyper-spectral cube given by such radiative transfer code can be made directly in GASS using the various post-treatment options implemented, such as calculation of moments or convolution with a beam. This makes GASS well suited to model and analyse both interferometric and single-dish data. This paper is focused on the results given by the association of GASS and LIME, a 3D radiative transfer code, and we show that the complex geometry observed in star-forming regions can be adequately handled by GASS+LIME.
Journal: MNRAS, 468, 685–702 (2017)
Submitted by: David Quénard
7.3 Todays new entry:
The Fabric of the Universe: Exploring the cosmic web in 3D prints and woven textiles
Benedikt Diemer & Isaac Facio
Abstract: We introduce The Fabric of the Universe, an art and science collaboration focused on exploring the cosmic web of dark matter with unconventional techniques and materials. We discuss two of our projects in detail. First, we describe a pipeline for translating three-dimensional density structures from N-body simulations into solid surfaces suitable for 3D printing, and present prints of a cosmological volume and of the infall region around a massive cluster halo. In these models, we discover wall-like features that are invisible in two-dimensional projections. Going beyond the sheer visualization of simulation data, we undertake an exploration of the cosmic web as a three-dimensional woven textile. To this end, we develop experimental 3D weaving techniques to create sphere-like and filamentary shapes and radically simplify a region of the cosmic web into a set of filaments and halos. We translate the resulting tree structure into a series of commands that can be executed by a digital weaving machine, and describe the resulting large-scale textile installation.
Journal: arXiv preprint server
URL of preprint: https://arxiv.org/abs/1702.03897
Submitted by: Benedikt Diemer
7.2 Today´s new entry:
Cosmography and Data Visualization
Daniel Pomarede, Helene M. Courtois, Yehuda Hoffman, R. Brent Tully
Abstract: Cosmography, the study and making of maps of the universe or cosmos, is a field where visual representation benefits from modern three-dimensional visualization techniques and media. At the extragalactic distance scales, visualization is contributing in understanding the complex structure of the local universe, in terms of spatial distribution and flows of galaxies and dark matter. In this paper, we report advances in the field of extragalactic cosmography obtained using the SDvision visualization software in the context of the Cosmicflows Project. Here, multiple visualization techniques are applied to a variety of data products: catalogs of galaxy positions and galaxy peculiar velocities, reconstructed velocity field, density field, gravitational potential field, velocity shear tensor viewed in terms of its eigenvalues and eigenvectors, envelope surfaces enclosing basins of attraction. These visualizations, implemented as high-resolution images, videos, and interactive viewers, have contributed to a number of studies: the cosmography of the local part of the universe, the nature of the Great Attractor, the discovery of the boundaries of our home supercluster of galaxies Laniakea, the mapping of the cosmic web, the study of attractors and repellers.
Journal or Name of Publication: PASP Special Focus Issue: Techniques and Methods for Astrophysical Data Visualization, in press
URL of preprint: https://arxiv.org/abs/1702.01941
Submitted by: Daniel Pomarede
7.1 Today´s new entry:
Catching a Grown-Up Starfish Planetary Nebula: I. Morpho-Kinematical study of PC 22
Sabin L., Gómez-Muñoz M. A., Guerrero M. A., Zavala S., Ramos-Larios G., Vázquez R., Corral L., Blanco Cárdenas M.W., Guillén P.F., Olguín L., Morisset C., Navarro S.
Abstract: We present the first part of an investigation on the planetary nebula (PN) PC 22 which focuses on the use of deep imaging and high resolution echelle spectroscopy to perform a detailed morpho-kinematical analysis. PC 22 is revealed to be a multipolar PN emitting predominantly in [O III] and displaying multiple non-symmetric outflows. Its central region is found to be also particularly inhomogeneous with a series of low ionization structures (knots) located on the path of the outflows. The morpho-kinematical model obtained with SHAPE indicates that i) the de-projected velocities of the outflows are rather large, > 100 km/s, while the central region has expansion velocities in the range ~25 to ~45 km/s following the “Wilson effect”, ii) the majority of the measured structures share similar inclination, ~100 degrees, i.e. they are coplanar, and iii) all outflows and lobes are coeval (within the uncertainties). All these results make us to suggest that PC 22 is an evolved starfish PN. We propose that the mechanism responsible for the morphology of PC 22 consists of a wind-shell interaction, where the fast post-AGB wind flows through a filamentary AGB shell with some large voids.
Journal: Monthly Notices of the Royal Astronomical Society, in press
Comments: 11 pages, 9 figures, Rep.Fig.7
URL of preprint: http://arxiv.org/abs/1702.00029
Submitted by: Laurence Sabin
The other day I was researching literature for a new paper and came across an unexpected treasure on the web that I would like to share here.
David Nadeau is a name that I remember very well as the lead author of the incredible animation of the Orion Nebula that he and a team of astronomers and computer scientists created in 1999 for the Hayden Planetarium at the Museum of Natural History in New York (Nadeau et al., 2001). It was so inspirational, I watched it over and over again.
Only now I stumbled upon a description of a second animation that Nadeau and his team did for the same planetarium a few years later. It is an animation that shows the formation of stars in a nebula and the evolution of the nebula and the circumstellar environment as stars are formed and illuminate the gas.
What I would like to call your attention to is David Nadeau´s description of the project, and in particular the challenges and problems that they faced to achieve their goal. They combine several high resolution simulations and were dealing with huge amounts of data, that were impossible to handle at first. So they came up with a few tricks to transfer and handle the data. These tricks are of interest to anyone who might embark on a similar project. Also, it discusses how one has to find trade-offs between the limitations of simulated data and their visualization for the general public that follows a particular script. Nature, even in a computer, doesn´t always do what we would like it to do.
So, I would like to encourage you to read Nadeau´s Case Study: Large data volume visualization of an evolving emission nebula.
In their project Nadeau et al. where not able to simulate the dynamical expansion of the nebula due to the photo-ionization from the recently formed star. Will Henney and colleagues did precisely such a simulation in 2011 for a research project (Arthur et al., 2011). The resultant phantastic movie was also used by the Hayden Planetarium in New York in their planetarium show “Journey to the stars“.
6.14 Today´s new entry:
A case study in astronomical 3D printing: The mysterious Eta Carinae
Thomas I. Madura
Abstract: 3-D printing moves beyond interactive 3-D graphics and provides an excellent tool for both visual and tactile learners, since 3-D printing can now easily communicate complex geometries and full color information. Some limitations of interactive 3-D graphics are also alleviated by 3-D printable models, including issues of limited software support, portability, accessibility, and sustainability. We describe the motivations, methods, and results of our work on using 3-D printing (1) to visualize and understand the Eta Car Homunculus nebula and central binary system and (2) for astronomy outreach and education, specifically, with visually impaired students. One new result we present is the ability to 3-D print full-color models of Eta Car’s colliding stellar winds. We also demonstrate how 3-D printing has helped us communicate our improved understanding of the detailed structure of Eta Car’s Homunculus nebula and central binary colliding stellar winds, and their links to each other. Attached to this article are full-color 3-D printable files of both a red-blue Homunculus model and the Eta Car colliding stellar winds at orbital phase 1.045. 3-D printing could prove to be vital to how astronomer’s reach out and share their work with each other, the public, and new audiences.
Journal: Publications of the Astronomical Society of the Pacific Focus Issue “Techniques and Methods for Astrophysical Data Visualization”
Comments: Accepted November 15, 2016, 17 pages, 9 figures, 5 embedded interactive 3-D figures. 3-D print files are included as ancillary material in the /anc subfolder on the arxiv. Rep. Fig. 7 or 8.
URL of preprint: https://arxiv.org/abs/1611.09994
Submitted by: T. Madura
6.13 Today´s new entry:
Space reconstruction of the morphology and kinematics of axisymmetric radio sources
P.N. Diep, N.T. Phuong, D.T. Hoai, P.T. Nhung, N.T. Thao, P. Tuan-Anh, P. Darriulat
Abstract: The unprecedented quality of the observations available from the Atacama Large Millimetre/sub-millimetre Array (ALMA) calls for analysis methods making the best of them. Reconstructing in space the morphology and kinematics of radio sources is an underdetermined problem that requires imposing additional constraints for its solution. The hypothesis of rotational invariance about a well-defined star axis, which is a good approximation to the description of the gas envelopes of many evolved stars and protostars, is particularly efficient in this role. In the first part of the article, a systematic use of simulated observations allows for identifying the main problems and for constructing quantities aimed at solving them. In particular the evaluation of the orientation of the star axis in space and the differentiation between expansion along the star axis and rotation about it are given special attention. The use of polar rather than Cartesian sky coordinates is shown to better match the morphology and kinematics of actual stars. The radial dependence of the gas density and temperature and the possible presence of velocity gradients are briefly considered. In the second part, the results obtained in the first part are applied to a few stars taken as examples with the aim of evaluating their usefulness when applied to concrete cases. A third part takes stock of what precedes and formulates some guidelines for modelling the radio emission of axisymmetric radio sources, limited however to the mathematics and geometry of the problem, physics considerations being ignored.
Journal: Monthly Notices of the Royal Astronomical Society (MNRAS), 461, 4276–4294 (2016)
Submitted by: Pham Ngoc Diep