%N colden
%D Calculates column densities for linear molecules
%P mchw
%: map analysis
%B
COLDEN is a MIRIAD task to calculate column densities. The maps
must have the same dimensions. The two images are compared on a
pixel by pixel basis, within a user defined region.
%A method
Three possibilities:
(1) Give one optically thin transition and the kinetic
temperature (Assumes tau=0). Enter in1, in2, J1, B1, mu,
scale1.
(2) Give two optically thin transitions with different J. The
calculation will assume LTE, calculate col. den. as in
(1), and fit to the best kinetic temperature and total
column density. Enter in1, J1, b1, scale1, in2, J2,
scale2, and mu (b1=b2).
(3) Give one optically thick and one less thick transition.
Assumes Tex(thick)=Tex(thin) and calculates optical depth
of less thick transition. Col. den. ensue. Enter in1,
J1, b1, scale1, in2, b2, scale2, and mu (J1=J2).
Default=1.
%A in1
The first input image contains the most abundant isotope
(e.g. 12CO).
The first plane must contain the integrated
intensity of the line (K-km/s) for methods 1 and 2, and the peak
temperature of the line (K) for method 3. No default
%A in2
For method 1, give the kinetic temperature in the first plane.
For method 2, this image contains the integrated intensity of
the second transition.
For method 3, the image contains the less abundant (thin)
isotope (e.g. 13CO). It contains at least three planes: the
peak temperature of the line, its center position, and its FWHM
width.
Use the output from program Gaufit. No default
%A region
Region to select data to compare from....(not implemented)
%A out
Output image. It consists of 7 planes; the meaning of the first
three depend on the method used:
(1) the first two planes are blank, the third is the column
density of the upper level of the transition,
(2) the first is the kinetic temperature, the next two the
column densities of the upper levels of each transition,
(3) the first is the optical depth of the less abundant
isotope, the second is the excitation temperature of the
abundant isotope, and the third is the column density of
the upper level of the line analyzed.
The remaining four planes are:
- the estimated total column density of the molecule,
- the column density of H2 inferred,
- the mass in each pixel, and
- a last plane in which every unmasked pixel is set to 1.
%A cut
Two values. Cutoff applied to data (i.e. column densities will
not be calculate for input parameter values less than cutoff).
Default=0.1 K, 0.1 km/s.
There is also a cutoff for values of temp > 1000K, v > 100 km/s.
Additionally, values for column densities greater than 1.0e+27
are not written to the output file.
%A b1
Value of B (in GHz) for the optically thick isotope.
Default=57.6 (12CO).
%A b2
Value of B (in GHz) for the optically thin isotope.
Default=55.1 (13CO).
%A j1
the rotational number of the upper level. Default J=1
%A j2
the rotational number of the upper level. Default J=2
%A mu
The dipole moment of the molecule (in Debye).
Default mu=0.112 (CO)
%A scale1
A constant that will multiply the peak temperatures in in1.
Default=1.0
%A scale2
A constant that will multiply the peak temperatures in in2.
Default=1.0
%A abund
The abundance of the less abundant isotope, relative to H2.
This will be used to compute the H2 column density.
Default=2.0e-06 (appropriate for 13CO in dark clouds).
%A dist
The distance of the source (in pc). It will be used to compute
the mass in each pixel from the H2 column density.
Default: 500 pc.
%A options
taulog: the optical depths are written as logs
collog: the column densities are written as logs
maslog: the masses are written as logs