Shape: A 3D Modeling Tool for Astrophysics

We present a flexible interactive 3D morpho-kinematical modeling application for astrophysics. Compared to other systems, our application reduces the restrictions on the physical assumptions, data type and amount that is required for a reconstruction of an object's morphology. It is one of the first publicly available tools to apply interactive graphics to astrophysical modeling. The tool allows astrophysicists to provide a-priori knowledge about the object by interactively defining 3D structural elements. By direct comparison of model prediction with observational data, model parameters can then be automatically optimized to fit the observation. The tool has already been successfully used in a number of astrophysical research projects.Comment: 13 pages, 11 figures, accepted for publication in the "IEEE Transactions on Visualization and Computer Graphics

Science Impacts of the SPHEREx All-Sky Optical to Near-Infrared Spectral Survey: Report of a Community Workshop Examining Extragalactic, Galactic, Stellar and Planetary Science

SPHEREx is a proposed SMEX mission selected for Phase A. SPHEREx will carry out the first all-sky spectral survey and provide for every 6.2" pixel a spectra between 0.75 and 4.18 $\mu$m [with R$\sim$41.4] and 4.18 and 5.00 $\mu$m [with R$\sim$135]. The SPHEREx team has proposed three specific science investigations to be carried out with this unique data set: cosmic inflation, interstellar and circumstellar ices, and the extra-galactic background light. It is readily apparent, however, that many other questions in astrophysics and planetary sciences could be addressed with the SPHEREx data. The SPHEREx team convened a community workshop in February 2016, with the intent of enlisting the aid of a larger group of scientists in defining these questions. This paper summarizes the rich and varied menu of investigations that was laid out. It includes studies of the composition of main belt and Trojan/Greek asteroids; mapping the zodiacal light with unprecedented spatial and spectral resolution; identifying and studying very low-metallicity stars; improving stellar parameters in order to better characterize transiting exoplanets; studying aliphatic and aromatic carbon-bearing molecules in the interstellar medium; mapping star formation rates in nearby galaxies; determining the redshift of clusters of galaxies; identifying high redshift quasars over the full sky; and providing a NIR spectrum for most eROSITA X-ray sources. All of these investigations, and others not listed here, can be carried out with the nominal all-sky spectra to be produced by SPHEREx. In addition, the workshop defined enhanced data products and user tools which would facilitate some of these scientific studies. Finally, the workshop noted the high degrees of synergy between SPHEREx and a number of other current or forthcoming programs, including JWST, WFIRST, Euclid, GAIA, K2/Kepler, TESS, eROSITA and LSST.Comment: Report of the First SPHEREx Community Workshop, http://spherex.caltech.edu/Workshop.html , 84 pages, 28 figure

Regularisierte Optimierungsverfahren für Rekonstruktion und Modellierung in der Computergraphik

The field of computer graphics deals with virtual representations of the real world. These can be obtained either through reconstruction of a model from measurements, or by directly modeling a virtual object, often on a real-world example. The former is often formalized as a regularized optimization problem, in which a data term ensures consistency between model and data and a regularization term promotes solutions that have high a priori probability. In this dissertation, different reconstruction problems in computer graphics are shown to be instances of a common class of optimization problems which can be solved using a uniform algorithmic framework. Moreover, it is shown that similar optimization methods can also be used to solve data-based modeling problems, where the amount of information that can be obtained from measurements is insufficient for accurate reconstruction. As real-world examples of reconstruction problems, sparsity and group sparsity methods are presented for radio interferometric image reconstruction in static and time-dependent settings. As a modeling example, analogous approaches are investigated to automatically create volumetric models of astronomical nebulae from single images based on symmetry assumptions.Das Feld der Computergraphik beschäftigt sich mit virtuellen Abbildern der realen Welt. Diese können erlangt werden durch Rekonstruktion eines Modells aus Messdaten, oder durch direkte Modellierung eines virtuellen Objekts, oft nach einem realen Vorbild. Ersteres wird oft als regularisiertes Optimierungsproblem dargestellt, in dem ein Datenterm die Konsistenz zwischen Modell und Daten sicherstellt, während ein Regularisierungsterm Lösungen fördert, die eine hohe A-priori-Wahrscheinlichkeit aufweisen. In dieser Arbeit wird gezeigt, dass verschiedene Rekonstruktionsprobleme der Computergraphik Instanzen einer gemeinsamen Klasse von Optimierungsproblemen sind, die mit einem einheitlichen algorithmischen Framework gelöst werden können. Darüber hinaus wird gezeigt, dass vergleichbare Optimierungsverfahren auch genutzt werden können, um Probleme der datenbasierten Modellierung zu lösen, bei denen die aus Messungen verfügbaren Daten nicht für eine genaue Rekonstruktion ausreichen. Als praxisrelevante Beispiele für Rekonstruktionsprobleme werden Sparsity- und Group-Sparsity-Methoden für die radiointerferometrische Bildrekonstruktion im statischen und zeitabhängigen Fall vorgestellt. Als Beispiel für Modellierung werden analoge Verfahren untersucht, um basierend auf Symmetrieannahmen automatisch volumetrische Modelle astronomischer Nebel aus Einzelbildern zu erzeugen

VLASSICK: The VLA Sky Survey in the Central Kiloparsec

At a distance of 8 kpc, the center of our Galaxy is the nearest galactic nucleus, and has been the subject of numerous key projects undertaken by great observatories such as Chandra, Spitzer, and Herschel. However, there are still no surveys of molecular gas properties in the Galactic center with less than 30" (1 pc) resolution. There is also no sensitive polarization survey of this region, despite numerous nonthermal magnetic features apparently unique to the central 300 parsecs. In this paper, we outline the potential the VLASS has to fill this gap. We assess multiple considerations in observing the Galactic center, and recommend a C-band survey with 10 micro-Jy continuum RMS and sensitive to molecular gas with densities greater than 10^4 cm^{-3}, covering 17 square degrees in both DnC and CnB configurations ( resolution ~5"), totaling 750 hours of observing time. Ultimately, we wish to note that the upgraded VLA is not just optimized for fast continuum surveys, but has a powerful correlator capable of simultaneously observing continuum emission and dozens of molecular and recombination lines. This is an enormous strength that should be fully exploited and highlighted by the VLASS, and which is ideally suited for surveying the center of our Galaxy.Comment: 13 pages, 3 figures, a White Paper submitted to provide input in planning the Very Large Array Sky Surve

Asymmetric Planetary Nebulae VII

This book contains the best and most up-to-date contributions in the field of late stage stellar evolution, as presented at the APNVII conference in Hong Kong in December 2017. A total of 60 scientists from 20 countries gathered to present, listen, interact and discuss the most current issues and problems in planetary nebulae and related objects research. The emphasis of this influential series of meetings, which was the seventh occasion over the last 20 years, has always been on the hypothesized and observed physical shaping mechanisms of the ejected nebulae that have such wonderful and intriguing forms. This special Galaxies conference issue of fully refereed contributions brings together a representative compilation of the meeting presentations in paper form. It captures the current “snap shot” status of this research field in some real sense. Such proceedings are well received and can be used as a reference material by both participants and all others working in the field for years to come

Science Impacts of the SPHEREx All-Sky Optical to Near-Infrared Spectral Survey: Report of a Community Workshop Examining Extragalactic, Galactic, Stellar and Planetary Science

SPHEREx is a proposed SMEX mission selected for Phase A. SPHEREx will carry out the first all-sky spectral survey and provide for every 6.2" pixel a spectra between 0.75 and 4.18 μm [with R∼41.4] and 4.18 and 5.00 μm [with R∼135]. The SPHEREx team has proposed three specific science investigations to be carried out with this unique data set: cosmic inflation, interstellar and circumstellar ices, and the extra-galactic background light. It is readily apparent, however, that many other questions in astrophysics and planetary sciences could be addressed with the SPHEREx data. The SPHEREx team convened a community workshop in February 2016, with the intent of enlisting the aid of a larger group of scientists in defining these questions. This paper summarizes the rich and varied menu of investigations that was laid out. It includes studies of the composition of main belt and Trojan/Greek asteroids; mapping the zodiacal light with unprecedented spatial and spectral resolution; identifying and studying very low-metallicity stars; improving stellar parameters in order to better characterize transiting exoplanets; studying aliphatic and aromatic carbon-bearing molecules in the interstellar medium; mapping star formation rates in nearby galaxies; determining the redshift of clusters of galaxies; identifying high redshift quasars over the full sky; and providing a NIR spectrum for most eROSITA X-ray sources. All of these investigations, and others not listed here, can be carried out with the nominal all-sky spectra to be produced by SPHEREx. In addition, the workshop defined enhanced data products and user tools which would facilitate some of these scientific studies. Finally, the workshop noted the high degrees of synergy between SPHEREx and a number of other current or forthcoming programs, including JWST, WFIRST, Euclid, GAIA, K2/Kepler, TESS, eROSITA and LSST

Science cases for a visible interferometer

High spatial resolution is the key for the understanding various astrophysical phenomena. But even with the future E-ELT, single dish instruments are limited to a spatial resolution of about 4 mas in the visible. For the closest objects within our Galaxy most of the stellar photosphere remains smaller than 1 mas. With the success of long baseline interferometry these limitations were soom overcome. Today low and high resolution interferometric instruments on the VLTI and CHARA offer an immense range of astrophysical studies. Combining more telescopes and moving to visible wavelengths broadens the science cases even more. With the idea of developing strong science cases for a future visible interferometer, we organized a science group around the following topics: pre-main sequence and main sequence stars, fundamental parameters, asteroseismology and classical pulsating stars, evolved stars, massive stars, active galactic nuclei (AGNs) and imaging techniques. A meeting was organized on the 15th and 16th of January, 2015 in Nice with the support of the Action Specific in Haute Resolution Angulaire (ASHRA), the Programme National en Physique Stellaire (PNPS), the Lagrange Laboratory and the Observatoire de la Cote d'Azur, in order to present these cases and to discuss them further for future visible interferometers. This White Paper presents the outcome of the exchanges. This book is dedicated to the memory of our colleague Olivier Chesneau who passed away at the age of 41

Simulating the Common Envelope Phase Using Moving-Mesh Hydrodynamics

Common envelope evolution (CEE) is a phase in the evolution of a binary system where a giant star and a smaller companion share a gaseous envelope, and is responsible for the formation of many systems of astrophysical interest. Despite its importance, CEE is not well understood due to the diverse physics involved. Astronomers have roughly modeled CEE using conserved quantities such as energy, but progress has been limited by uncertainties in the contributions of various energy sources. Thus, 3-D numerical simulations must be brought to bear. Here two methodologies are commonly employed, each of which comes with its own set of advantages: smoothed-particle hydrodynamics and Eulerian grid codes. A hybrid of these methods known as the moving-mesh code has been developed in an attempt to capture the best characteristics of each. We use the moving-mesh solver MANGA, which has recently been improved with the inclusion of physics modules relevant to CEE. We begin this work with an introduction to CEE in Chapter 1. We go through a step-by-step description of its four stages and summarize observations of transients that are thought to result from binary interactions. We then present an overview of simulation techniques in Chapter 2, showing how aspects of smoothed-particle hydrodynamics and Eulerian methods are implemented into moving-mesh schemes. We begin our numerical studies of CEE using MANGA in Chapter 3 and show that the ejection of the envelope is aided by the inclusion of hydrogen recombination and tidal forces. CEE simulations to date have neglected hydrodynamic interactions at the surface of the companion. As such, we discuss our development of moving boundary conditions in Chapter 4 and show how they can be used to model the companion object. We show that the orbital eccentricity is affected by the size of the companion through hydrodynamic torques. Finally, we describe our implementation of magnetohydrodynamics in Chapter 5. We find rapid amplification of a toroidal magnetic field at the onset of CEE, which is thought to assist in the formation of nebulae

The Inertial Range of Turbulence in the Inner Heliosheath and in the Local Interstellar Medium

The governing mechanisms of magnetic field annihilation in the outer heliosphere is an intriguing topic. It is currently believed that the turbulent fluctuations pervade the inner heliosheath (IHS) and the Local Interstellar Medium (LISM). Turbulence, magnetic reconnection, or their reciprocal link may be responsible for magnetic energy conversion in the IHS.   As 1-day averaged data are typically used, the present literature mainly concerns large-scale analysis and does not describe inertial-cascade dynamics of turbulence in the IHS. Moreover, lack of spectral analysis make IHS dynamics remain critically understudied. Our group showed that 48-s MAG data from the Voyager mission are appropriate for a power spectral analysis over a frequency range of five decades, from 5e-8 Hz to 1e-2 Hz [Gallana et al., JGR 121 (2016)]. Special spectral estimation techniques are used to deal with the large amount of missing data (70%). We provide the first clear evidence of an inertial-cascade range of turbulence (spectral index is between -2 and -1.5). A spectral break at about 1e-5 Hz is found to separate the inertial range from the enegy-injection range (1/f energy decay). Instrumental noise bounds our investigation to frequencies lower than 5e-4 Hz. By considering several consecutive periods after 2009 at both V1 and V2, we show that the extension and the spectral energy decay of these two regimes may be indicators of IHS regions governed by different physical processes. We describe fluctuations’ regimes in terms of spectral energy density, anisotropy, compressibility, and statistical analysis of intermittency.   In the LISM, it was theorized that pristine interstellar turbulence may coexist with waves from the IHS, however this is still a debated topic. We observe that the fluctuating magnetic energy cascades as a power law with spectral index in the range [-1.35, -1.65] in the whole range of frequencies unaffected by noise. No spectral break is observed, nor decaying turbulence