A typical user query will return about 50-100 models, which the user can then interactively filter as a function of 8 model parameters (e.g., extinction, size, flux, luminosity). A flexible, multi-dimensional plotter (Figure 1) allows users to view the models, rotate them, tag specific parameters with color or symbol size, and probe individual model points.
For any given model, auxiliary plots such as dust grain properties, radial intensity profiles, and the flux as a function of wavelength and beamsize can be viewed. The user can fit observed data to several models simultaneously and see the results of the fit; the best fit is automatically selected for plotting.
The URL for this project is http://dustem.astro.umd.edu.
The database is kept on disk in a directory structure that uniquely
specifies each model parameter. Thus a search through the database is
extremely fast: simply chdir to the correct directory
and file glob on subdirectories to return the models which match the user inputs.
The model files (9 per model - primary and 8 auxiliary) are kept in a
single file in TGZ (tar, gzipped) format (primarily due to inode limitations), and
when requested are untarred in a temporary directory. (This
untarring process is a little slow for 
100 models and we are working
on ways to speed it up by parallelizing it - suggestions welcome!). The
ASCII contents of the primary files are then sent through a stream to
the DIRT applet, where they are loaded into the 3-D plotter (Figure 1).
Subsequent requests for auxiliary files for any model (e.g. in the Details Window)
are handled the same way. The search, untar, and stream
reply are done via Perl CGI scripts.
Say the user specified an Envelope model, MRN Grains, Density Law = 0.0, Luminosity = 100, Effective Temperature = 40000, and Outer Radius = 5E14. The directory to chdir to is
envelope/MRN/D-0.0/L1.00E+02/T4.00E+04/O5.00E+14/
All subdirectories below this contain models which match the inputs, but have varying Visual Extinction (A) and Inner Radius (I):
A1.00E+00
/I1.00E+13/models.tgz
/I3.00E+13/models.tgz
A1.00E+01
/I1.00E+13/models.tgz
/I3.00E+13/models.tgz
.
.
.
A5.00E+02
/I1.00E+13/models.tgz
/I3.00E+13/models.tgz
Each models.tgz file is untarred into the temporary
area on the server, from which the model data are transferred to the
client applet. Note this directory structure allows for insertion
of new models at any point in the tree.
At runtime, the Java applet queries a short index to determine what
models are currently available and can be presented as choices to the
user. The index is kept up to date by a daily crontab.
The envelope models contained in DIRT are based on the transfer code of Wolfire & Cassinelli (1986). The code solves for the grain temperatures and the emitted spectral energy distribution of a spherical dust shell under the constraints of thermal and radiative equilibrium.
The Details Window displays auxiliary data associated with a chosen model (selected by a mouse-click in the Plot Controller). These are model outputs that have been calculated along with the spectral energy distribution, such as grain temperatures, gas density, and flux as a function of both frequency and beamsize.
The user finds the best-fit model to her data using the Chi-Squared Fit Window. Either total flux as a function of frequency or flux as a function of both frequency and beamsize can be fit and the best-fit model (based on a chi-squared statistic) is displayed along with the data.
Both of these windows make use of the Java two-dimensional plotting package PtPlot developed at U.C. Berkeley. PtPlot has a few annoying idiosyncrasies (e.g., plot symbol colors are declared static), but is generally a pretty good package.
Development of DIRT was supported in part by
NASA ADP grant NAG5-6750.
Teuben, P. J., et al. 2000, this volume, 644
Wolfire, M. & Cassinelli 1986, ApJ, 310, 207
