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pspeed - calculate the pattern speed of a stellar system.


pspeed int=ccd-intensity vel=ccd-velocity [parameter=value]


pspeed calculates the pattern speed of a stellar system using Tremaine & Weinberg’s method (1984ApJ...282L...5T). For this a line parallel but offset to the line of nodes of a galaxy must have information on intensity and radial velocity. pspeed assumes the line of nodes is along the X-axis.

In the following (x,y) are defined along the major and minor axis of the galaxy resp., and pspeed will then compute the numerical sums

        V(y) =  SUM ( vel(x,y) * den(x,y)) / SUM ( den(x,y) )
        X(y) =  SUM ( x * den(x,y)) / SUM ( den(x,y) )
where the summation is along x. This will result in a correlation
    V = Omega * SIN(inc) * X
The output will be a table


The following parameters are recognized in any order if the keyword is also given:
input file, must be the intensity in image(5NEMO) format [no default].
input file, must be the radial velocity in image(5NEMO) format [no default].
Will produce a table how the numerical integration along only one specific y value resulted in a pattern speed. For debugging only. [default: -1, i.e. not used].


pspeed is too sensitive to noise to be useful for all practical purposes.

See Also

snapslit(1NEMO) , snaprotate(1NEMO) , snapshot(5NEMO) , image(5NEMO)


Peter Teuben


~/src/pjt/image      authors original sources

Update History

17-Aug-87    V1.0: Original created    PJT
 1-Nov-87    V1.2: more debug output PJT

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