3D Astrophysics Newsletter

2018_harvey9.1 Today´s new entry:

Polarimetry and Spectroscopy of the `Oxygen Flaring’ DQ Herculis-like nova: V5668 Sagittarii (2015)

E. J. Harvey, M. P. Redman, M. J. Darnley, S. C. Williams, A. Berdyugin, V. E. Piirola, K. P. Fitzgerald, E. G. P. O’ Connor

Abstract: Context. Classical novae are eruptions on the surface of a white dwarf in a binary system. The material ejected from the white dwarf surface generally forms an axisymmetric shell of gas and dust around the system. The three-dimensional structure of these shells is difficult to untangle when viewed on the plane of the sky. In this work a geometrical model is developed to explain new observations of the 2015 nova V5668 Sagittarii.
Aims. We aim to better understand the early evolution of classical nova shells in the context of the relationship between polarisation, photometry and spectroscopy in the optical regime. To understand the ionisation structure in terms of the nova shell morphology and estimate the emission distribution directly following the light-curve’s dust-dip.
Methods. High-cadence optical polarimetry and spectroscopy observations of a nova are presented. The ejecta is modelled in terms of morpho-kinematics and photoionisation structure.
Results. Initially observational results are presented, including broadband polarimetry and spectroscopy of V5668 Sgr nova during eruption. Variability over these observations provides clues towards the evolving structure of the nova shell. The position angle of the
shell is derived from polarimetry, which is attributed to scattering from small dust grains. Shocks in the nova outflow are suggested in the photometry and the effect of these on the nova shell are illustrated with various physical diagnostics. Changes in density and temperature as the super soft source phase of the nova began are discussed. Gas densities are found to be of the order of 10^9 cm−3 for the nova in its auroral phase. The blackbody temperature of the central stellar system is estimated to be around 2.2 × 105 K at times coincident with the super soft source turn-on. It was found that the blend around 4640 Å commonly called ‘nitrogen flaring’ is more naturally explained as flaring of the O ii multiplet (V1) from 4638 – 4696 Å, i.e. ‘oxygen flaring’.
Conclusions. V5668 Sgr (2015) was a remarkable nova of the DQ Her class. Changes in absolute polarimetric and spectroscopic multi-epoch observations lead to interpretations of physical characteristics of the nova’s evolving outflow. The high densities that were found early-on combined with knowledge of the system’s behaviour at other wavelengths and polarimetric measurements strongly suggest that the visual ‘cusps’ are due to radiative shocks between fast and slow ejecta that destroy and create dust seed nuclei cyclically.

Journal: Astronomy & Astrophysics
URL of preprint: https://arxiv.org/abs/1802.00224
Comments: Accepted 22 November 2017, 17 pages, 13 figures, 3 tables
Submitted by: Eamonn Harvey


3D Astrophysics Newsletter

2017_8_2_arcand8.2 Today´s new entry:

Bringing Cosmic Objects Down to Earth: An Overview of 3D Modelling and Printing in Astronomy and Astronomy Communication

Kimberly Arcand, Megan Watzke, Joseph DePasquale, April Jubett, Peter Edmonds, Kristin DiVona

Abstract: Three-dimensional (3D) modelling is more than just good fun, it offers a new vehicle to represent and understand scientific data and provides experts and non-experts alike the ability to manipulate models and gain new perspectives on data. This article explores the use of 3D modelling and printing in astronomy and astronomy communication and looks at some of the practical challenges, and solutions, to using 3D modelling, visualisation and printing in this way.

Journal: Communication Astronomy with the Public (CAPjournal)
URL: https://www.capjournal.org/issues/22/22_14.pdf
Submitted by: Kimberly Arcand 

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