3D Astrophysics Newsletter

2017_8_1_yan8.1 Today´s new entry:

Towards a three-dimensional distribution of the molecular clouds in the Galactic Centre

Qing-Zeng Yan, A. J. Walsh, J. R. Dawson, J. P. Macquart, R. Blackwell, M. G. Burton, G. Rowell, Bo Zhang, Ye Xu, Zheng-Hong Tang, P. J. Hancock

Abstract: We present a study of the three-dimensional structure of the molecular clouds in the Galactic Centre (GC) using CO emission and OH absorption lines. Two CO isotopologue lines, 12CO (J=1-0) and 13CO (J=1-0), and four OH ground-state transitions, surveyed by the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH), contribute to this study. We develop a novel method to calculate the OH column density, excitation temperature, and optical depth precisely using all four OH lines, and we employ it to derive a three-dimensional model for the distribution of molecular clouds in the GC for six slices in Galactic latitude. The angular resolution of the data is 15.5 arcmin, which at the distance of the GC (8.34 kpc) is equivalent to 38 pc. We find that the total mass of OH in the GC is in the range 2400-5100 Solar mass. The face-on view at a Galactic latitude of b=0° displays a bar-like structure with an inclination angle of 67.5±2.1° with respect to the line of sight. No ring-like structure in the GC is evident in our data, likely due to the low spatial resolution of the CO and OH maps.

Journal: Monthly Notices of the Royal Astronomical Society (MNRAS), accepted
 Accepted (07 July 2017), 15 pages, 12 figures
URL of preprint: https://arxiv.org/pdf/1707.02378.pdf
Submitted by: Qing-Zeng Yan

3D Astrophysics Newsletter

Summary of the first half of 2017:

7.1 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.

7.2 Cosmography and Data Visualization
Daniel Pomarede, Helene M. Courtois, Yehuda Hoffman, R. Brent Tully

7.3 The Fabric of the Universe: Exploring the cosmic web in 3D prints and woven textiles
Benedikt Diemer & Isaac Facio

7.4 Modelling the 3D physical structure of astrophysical sources with GASS
David Quénard, Sandrine Bottinelli, Emmanuel Caux

7.5 Hybrid polygon and hydrodynamic nebula modeling with multi-waveband radiation transfer in astrophysics
Wolfgang Steffen & Nico Koning

7.6 Reconstruction of a helical prominence in 3D from IRIS spectra and images
B. Schmieder, M. Zapiór, A. López Ariste, P. Levens, N. Labrosse, R. Gravet

3D Astrophysics Newsletter

2017_7_7_vohl7.7 Today´s new entry:

Real-time colouring and filtering with graphics shaders

Dany Vohl, Christopher J. Fluke, David G. Barnes, Amr H. Hassan

Abstract: Despite the popularity of the Graphics Processing Unit (GPU) for general purpose computing, one should not forget about the practicality of the GPU for fast scientific visualisation. As astronomers have increasing access to three dimensional (3D) data from instruments and facilities like integral field units and radio interferometers, visualisation techniques such as volume rendering offer means to quickly explore spectral cubes as a whole. As most 3D visualisation techniques have been developed in fields of research like medical imaging and fluid dynamics, many transfer functions are not optimal for astronomical data. We demonstrate how transfer functions and graphics shaders can be exploited to provide new astronomy-specific explorative colouring methods. We present 12 shaders, including four novel transfer functions specifically designed to produce intuitive and informative 3D visualisations of spectral cube data. We compare their utility to classic colour mapping. The remaining shaders highlight how common computation like filtering, smoothing and line ratio algorithms can be integrated as part of the graphics pipeline. We discuss how this can be achieved by utilising the parallelism of modern GPUs along with a shading language, letting astronomers apply these new techniques at interactive frame rates. All shaders investigated in this work are included in the open source software
shwirl (Vohl 2017).

Journal: Monthly Notices of the Royal Astronomical Society (MNRAS),  accepted for publication
Comments: Accepted on 30 June 2017, 24 pages, 19 figures, 14 algorithms, 1 table
URL: Download preprint
Submitted by: Dany Vohl

3D Astrophysics Newsletter

2017_7_6_schmieder7.6 Today´s new entry:

Reconstruction of a helical prominence in 3D from IRIS spectra and images

B. Schmieder, M. Zapiór, A. López Ariste, P. Levens, N. Labrosse, R. Gravet

Context: Movies of prominences obtained by space instruments e.g. the Solar Optical Telescope (SOT) aboard the Hinode satellite and the Interface Region Imaging Spectrograph (IRIS) with high temporal and spatial resolution revealed the tremendous dynamical nature of prominences. Knots of plasma belonging to prominences appear to travel along both vertical and horizontal thread-like loops, with highly dynamical nature.
Aims: The aim of the paper is to reconstruct the 3D shape of a helical prominence observed over two and a half hours by IRIS.
Methods: From the IRIS Mg ii k spectra we compute Doppler shifts of the plasma inside the prominence and from the slit-jaw images (SJI) we derive the transverse field in the plane of the sky. Finally we obtain the velocity vector field of the knots in 3D.
Results: We reconstruct the real trajectories of nine knots travelling along ellipses.
Conclusions: The spiral-like structure of the prominence observed in the plane of the sky is mainly due to the projection effect of long arches of threads (up to 8 × 10e4 km). Knots run along more or less horizontal threads with velocities reaching 65 km/s. The dominant driving force is the gas pressure.

Journal: Astronomy & Astrophysics,  accepted for publication
URL: Download preprint
Submitted by: Maciej Zapiór

3D Astrophysics Newsletter

2017_steffen_2507.5 Today´s new entry:

Hybrid polygon and hydrodynamic nebula modeling with multi-waveband radiation transfer in astrophysics

Wolfgang Steffen & Nico Koning

Abstract: We demonstrate the potential for research and outreach of mixed polygon and hydrodynamic modeling and multi-waveband rendering in the interactive 3-D astrophysical virtual laboratory Shape. In 3-D special effects and animation software for the mass media, computer graphics techniques that mix polygon and numerical hydrodynamics have become commonplace. In astrophysics, however, interactive modeling with polygon structures has only become available with the software Shape. Numerical hydrodynamic simulations and their visualization are usually separate, while in Shape it is integrated with the polygon modeling approach that requires no programming by the user. With two generic examples, we demonstrate that research and outreach modeling can be achieved with techniques similar to those used in the media industry with the added capability for physical rendering at any wavelength band, yielding more realistic radiation modeling. Furthermore, we show how the hydrodynamics and the polygon mesh modeling can be mixed to achieve results that are superior to those obtained using either one of these modeling techniques alone.

Journal: Astronomy and Computing, in press
Comments: download accompanying mpeg movie here
URL: Download preprint
Submitted by: W. Steffen

Pigeon stereo

tumblr_o35y2fZI7O1t1ig6no7_400.gifThe other day I overheard a discussion between me and myself about pigeons. It was more about what their eyes and brains see when they walk back and forth picking up breadcrumbs that little kids and their granddads throw on the ground in front of a park bench. We have all seen it, haven´t we?

It´s like a discussion in stereo, you and yourself take a slightly different angle on a subject and discuss it vigorously in your head. The result is a confusing, but a slightly more complete picture of the matter. Continue reading

3D Astrophysics Newsletter

2017_7_4_quenard7.4 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)
URL: https://doi.org/10.1093/mnras/stx404
Submitted by: David Quénard