ARTIST tutorial: a first simple session
This ARTIST tutorial describes a first simple session of ARTIST and
LIME. You will see how to run the molecular excitation calculation
from the CASA prompt, after selecting the model and its
parameters. Then you will see how to create a FITS cube of the
molecular line radiation, after selecting the source distance and
orientation and transition of interest. Finally, you will inspect the
resulting cube.
Requirements:
For this example you will need a molecular data file (hco+.dat) and a dust
opacity table (jena_thin_e6.dat). Download the files from the links provided in the
previous sentence, and place the files in your working directory.
Other molecular data files can be obtained from the Leiden
Atomic and Molecular Database (LAMDA).
Selecting the model and setting up the LIME parameters
The first example adopts the Bonnor Ebert (http://adsabs.harvard.edu/
abs/1955ZA.....37..217E and http://adsabs.harvard.edu/abs/1956MNRAS.
116..351B) sphere is used to generate an image cube of the HCO+ 1-0 line
from an infalling sphere. The first step is to use the task limesover generate the
physical model. The input parameters are shown below. The task performs the
following
- Passes the parameters to the BonnorEbert56 function within the modellib
package of ARTIST.
- The model is passed to LIME where the grids are generated and the
molecular excitation is calculated.
- A model grid is produced at the end of the task where it contains the LIME
grid points, density, temperature, and level populations for the specified
molecule.
The Bonnor Ebert sphere model has a self-consistent temperature and velo-
city structures. There is no need to insert temperature and velocity functions
unless the user wants to modify them. The task will overwrite the self-consistent
values with the given parameters.
# In CASA
inp limesolver
radius = 3.0857e16
minScale = 1.496e13
sinkPoints = 2000
pIntensity = 5000
nSolveIters = 12
moldatfile = [`hco+.dat']
dust = `jena_thin_e6.tab'
gridOutFile = "BE56_test.fits"
modelID = `BonnorEbert56'
T = 50
rhoc = 5e6
bmag = "vectorConstR"
bmag args = [0.0]
abundance = "scalarConst"
abundance args = [1e-9]
doppler = "scalarConst"
doppler args = [300.]
For now, we will not worry about the meaning of these parameters. They
simply serve as a an example to illustrate ARTIST.
Now you can simply start the task by typing
# In CASA
go
This will launch the CASA task limesolver, which will
start to geerate the grid and calculate the level populations. In the
example above, 12 iterations will be performed, which will take
approximatel XXX minutes on a modern desktop computer.
The output will appear in the CASA Logger
CASA Logger output here
After limesolver has completed it will have written the
level popualtions at all grid points in the file
BE56_test.fits in your working directory.
Setting up the imaging parameters and creating the output FITS
cube
The level populations calculated above serve as input for the next
step, where we solve the radiation transfer through the source and
calculate the emission as a FITS cube. We do this by using the CASA
task raytrace as follows
# In CASA
inp raytrace
gridInFile = 'BE56_test.fits'
moldatfile = ['hco+.dat']
dust = 'jena_thin_e6.tab'
filename = 'BE56_hcop_1.fits'
imgres = 0.05
pxls = 128
distance = 3.08572e20
doLine = True
nchan = 50
velres = 500.0
trans = 0
source vel = 3500.0
Again, we start the calculation by typing
# In CASA
go<.br>
The output will appear in the CASA Logger
CASA Logger output here
The output FIST cube will appear after a few minutes in your
working directory, with the name BE56_hcop_1.fits.
Inspection and further processing of the output FITS cube
(To be written)
Back to the main ARTIST page
Last modified: Fri Dec 1 13:10:30 CET 2017