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data.cube
such as closure of isovelocity contours
along the major axis and twists in channel maps showing the minor axis).
The velocity rotation profile in the plane of the disk may be suggested
by inspection of position-velocity maps made with velplot. For the purpose of
this exercise we will assume a flat rotation velocity profile in the plane
of the disk of 150 km/s. So we make the 3-dimensional data cube for each tilted
ring with velimage
and add them together with maths.
VELIMAGE | |
in=aaa,vvv | |
sigma=10 | Velocity dispersion,mandatory if no 3rd image above |
nchan=64 | Number of velocity channels in the output cube |
start=230 | Velocity at channel 1 |
step=6.6 | Velocity increment between channels |
out=model.cube | The output cube |
options=relax | Usually necessary in this type of scheme. |
Obviously, prior to running velimage, we must have generated
the input files aaa
and vvv
which contain our assumptions about
the variation in intensity and velocity in our model.
aaa
is the (x,y) intensity distribution of what will be
model.cube
integrated over the z-axis. In this example it is an elliptical annulus of
uniform intensity made by subtracting an inner disk from an outer disk using
maths, the disks having been made using imgen
as follows :
IMGEN | |
out=aao | Output dataset. |
object=disk | Disk model. |
spar=0.01,0,-60,1000,500,30 | Source parameters, 10 mJy intensity annulus, |
centred 60 arcsec south of the image centre, | |
major axis=1000 arcsec,minor axis=500 arcsec | |
major axis pa=30 degrees | |
imsize=128,128 | Image size. |
cell=30,30 | Cell size in arcsec. |
IMGEN | |
out=aai | The outer dataset. |
object=disk | Disk model. |
spar=0.01,0,-60,1000,500,30 | Source parameters, 10 mJy intensity annulus, |
centred 60 arcsec south of the image centre, | |
major axis=1000 arcsec,minor axis=500 arcsec | |
major axis pa=30 degrees | |
imsize=128,128 | Image size. |
cell=30,30 | Cell size in arcsec. |
IMGEN | |
out=aai | The inner disk. |
object=disk | Disk model again. |
spar=0.01,0,-60,800,400,30 | Similar parameters, but smaller radii. |
imsize=128,128 | Same image size and |
cell=30,30 | resolution. |
MATHS | |
exp=(aao-aai) | Generate a annulus. |
out=aaa | Output dataset name. |
vvv
is a model for the velocities (z-axis) made using velmodel.
VELMODEL | |
in=data.cube | Template input. |
pa=30 | |
incline=65 | |
radius=30 | |
vrot=150 | |
vsys=440 | |
out=vvv |
Note that the input (data.cube
in the above) a template only but if
you use your actual data cube you will finally end up with a model
with much of the header information the same as the data, e.g. it will
appear to be in the same position in the sky.
One makes a number of such model.cubes
and adds them together
with maths
to obtain the final 3-dimensional tilted ring model.
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