AISRP 1999 Workshop
(Applied Information Systems Research Program)

28--29 September 1999, Boulder, CO

Priscilla Frisch and Andrew Hanson
University of Chicago and Indiana University

Abstract
We are developing a variety of virtual reality tools and techniques to demonstrate the time-variable astrophysical properties of the local galactic neighborhood of the Sun. Our simulations will integrate a wide range of data sources and models of their spacetime properties. We target visualization environments ranging from desktop graphics and the CAVE immersive virtual reality system to volume visualization applications and methods for scientific collaboration over the Web. Our visualization tools are currently in the development stage, and we show first results and discuss the relevant data being considered for inclusion in the analysis.

Outline

• Overall Goals
• Scientific Objectives
• Visualization Design
• Plans

Overall Goals

The goal of this project is to construct intuitive visual representations of the astrophysical data pertinent to the near galactic environment of our Sun and to make them available as tools to scientists and educators.

Scientific Objective of Soljourn Project:

• Constraining Past and Future Interplanetary Environments of Planetary Systems

Interactive 3D graphical representations can provide insights into the dynamical interactions of stars and interstellar matter in the local galactic neighborhood of the Sun, and hence the interplanetary environments of nearby planetary systems. These insights help us to understand:

• The dynamic interactions of stellar winds and interstellar clouds, which determine interplanetary environments
• Stellar space trajectories, predictable from data and models, for time scales on the order of a few million years
• Interstellar cloud dynamics, diffuse and molecular, and relation to star-formation and spiral arm pattern
• The time-variable galactic environment of the Sun, which travels about 20 parsecs per million years through the LSR
• The time-variable properties of interplanetary environments, including the larger flux of raw interstellar material onto the surfaces of outer planets when compared to inner planets

• Stellar and Interstellar Cloud Dynamics
• Stellar 3D space motions are easy to determine: use proper motions, distances, radial velocities
• Interstellar cloud 3D space motions much harder to define
• Define diffuse interstellar clouds with HI 21 cm data
• Define molecular clouds with CO data
• Establish cloud locations in space and radial velocities from absorption spectra (e.g., UV, optical absorption lines using stars of known distances)
• Define individual interstellar clouds and reconstruct tangential velocities of interstellar clouds using intuition, absorption line data, morphological features, and proximity to star forming regions
• Ultimate goal: Define individual interstellar clouds and reconstruct tangential velocities of interstellar clouds using superbubble models for diffuse clouds, spiral motion modelsfor molecular clouds

• Soljourn Software Tools - Relate Stars and Interstellar Clouds, Interactively Relocate Interstellar Clouds within Soljourn Model based on Data

• Use family of tools to identify star-cloud interactions and the astrophysical properties of these interactions
• Need family of tools to "define individual interstellar clouds", or cloud complexes
• Need family of tools to interactively "move" these defined-clouds within the Soljourn model based on absorption line data
• Need tools to generate global astrosphere properties based on galactic environment of star (first order estimate based on pressure balance; beyond that collaborative effort required)
• Identify stars useful for constraining individual cloud dynamics, properties (e. g. shadowing)
• Identify stars likely to have accreted ISM in past

• Data Sources
• Zeroth order stellar data are Bright Star Catalogue stars enhanced with Hipparchos distances
• Need additional data on stellar velocities
• Need data on stellar activity levels for astrosphere estimates
• Ultimately, a Soljourn-specific star catalogue with requisite data
• HI clouds defined by 21-cm data (e.g. Leiden data, Heiles composite maps)
• Ultimately: add Reynolds WHAM H-alpha emission line all-sky survey?
• Molecular clouds defined by CO data (e.g. Dame, Thaddeus, others CO surveys)
• Sellar data will include best astrometric data (Hipparchos, Tycho, distances, proper motions); radial velocities (collaborative efforts needed to obtain new data??)
• Enhance data-base with specific objects of interest to others (e.g. pulsar proper motion data)
• Cross index stars in Soljourn database to interstellar absorption line data in other databases (e.g. UV data, optical data)
• Ultimately: Create database of optical absorption lines or cross-link to data-bases maintained by other scientists
• Don't "reinvent the wheel": collaborate with others to introduce data into Soljourn model

• Heliopause and Astrospheres
• Local: The heliosphere properties dominated by interstellar ion, magnetic (?), presssures (including charge-exchange between protons, HI atoms in heliosheath regions
• Local: Heliosphere properties predictable over past and future galactic environments of Sun
• Local: Heliosphere relatively large while in Local Bubble, and blue-shifted cloud towards Sirius; relatively large (radius about 100 AU) today; small if denser (10 atoms/cc, other properties same) cloud encountered
• General: Astrosphere properties function of total (including ram) pressure of ambient interstellar cloud and stellar activity levels (e.g. stellar winds)
• General: Need data on stellar activity levels; cross-link to (or incorporate into) Soljourn database?
• General: Pressure equilibrium gives approximate astrosphere dimensions once relative pressure balance betweeen stellar winds and ambient interstellar clouds known
• Interstellar dust: Grains with radii greater than 0.2 microns focused/defocused inside solar system (e.g. Ulysses data, models); largest grains focussed downwind of Sun (Earth passes through focussing cone about November); smallest charged grains (less than 0.1 micron) excluded from heliosphere; expect similar effect for other stars

• Plans
• Make the rudimentary dynamical model of stars and interstellar clouds in the LSR a basis for soliciting input from scientists interested in special regions and objects
• Need feedback on types of visualization tools that would support these tasks
• Prototypes involve 3D Web graphics, immersive Virtual Reality Environments, volume visualization tools, collaborative tools
• Examples: Next part of presentation
• Questions, suggestions?

Visualization Design

The visualization tools for this project are being developed in response to the data sources. Data analysis and reduction is proceeding hand-in-hand with tools whose need is suggested by the properties of the data.

• Data Demands
• Stellar data: need accurate 3D positions and velocities - develop Soljourn-specific database
• Stellar properties: need radial velocity data, spectral properties, activity levels
• Gas cloud absorption: need to understand how to define "interstellar cloud complexes" and small scale structure of interstellar clouds
• HI data: HI clouds are highly dynamical; need tools for time-dependent volume visualization of dynamic diffuse objects
• HI data: need tools for velocity parsing of 21-emission features into 3D clouds; use Gaussian-velocity profiles??; ignore small-scale structure, possible turbulence??
• Implied HI gas density: a second-step volume visualization problem
• CO data tools easier than HI data since at rest in LSR and velocity dispersion (locally) less than 1 km/s; densities approximated; reconstruct cloud morphology from distance, space density, column density
• Heliopause data: 2D scalar field volume vis problem

• Visualization Demands
• Stars: develop methods for keeping context: constellation positions, 3D positions, proper motions have conflicting display requirements
• Star selection: need to filter star properties for task
• Context establishment: galactic equator, (l,b) grid, radial scale
• Data selection: need to turn properties and tools on and off
• Interaction and animation: dynamically explore many viewpoints, control time steps of animations
• Show scientifically meaningful layers of volume data
• Exploit 3D image processing tools to select gas, heliosphere features

• Visualization Environments
  We plan to exploit desktop graphics, the CAVE immersive virtual reality environment, and volume visualization tools, as well as exploring methods for scientific collaboration over the Web.
• Desktop: Standard workstation and " fishtank " VR
• CAVE: Indiana University, UI Chicago, Argonne, UIUC have fully immersive 4-wall head-tracked stereo display environments
• Desktop Volume Visualization: IU and other research groups (e.g., Vis5D, possibly Mitsubishi) have desktop volume data systems
• CAVE Volume Visualization: IU has developed volume system usable for HI data and heliosphere data
• Collaborative Visualization: several families of techniques available: desktop Java/EAI works with VRML, and CavernSoft works with CAVE

• Software Choices
• Local: SGI OpenGL and Performer based systems usable for specific applications; OpenGL volume visualizer developed at IU; CAVE system with OpenGL and pfCAVE Performer system.
• Web-based: Cosmoplayer on SGI and PC's in Netscape allow sharing of complex 3D VRML data sets and animations with no software development
• Combined: Adding Java/EAI permits extension to collaboration.
• special VRML browser: existing UI Chicago system for CAVE VRML display being extended to support this project (giving display of same data on desktop and CAVE)

• Collaboration Support
  WEB-based collaboration identified as a strong need; need to have simultaneous 3D views to support science objectives.
• Constrained navigation: IU research on guiding collaborators through difficult environments: several published papers
• Following the Leader: Methods of attaching collaborators to leader and controlling gaze
• Detaching from Leader: Methods of letting collaborators go off on their own and rejoin "Tour Group" at will
• Environments: Java/EAI/VRML Web support on desktop, pfCAVE/Performer/CavernSoft system for high-performance CAVE collaboration
• Goals: Get sense of presence, support scientific process of exchanging brainstorm information on the problem.

• Build Soljourn Database. Continue accumulation of data sources enabling overview of local galactic environment
• Data Analysis. Extract pertinent data and convert for display environments
• Visualization and Intuition Building: continue seeking high-intuition display, animation, and interaction techniques to support scientific goals
• Collaborative Tools. Solicit input for model; Help scientists view data collaboratively to exchange insights

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