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Basic Information on colden
Task: colden
Purpose: Calculates column densities for linear molecules
Categories: map analysis
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.
Key: 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.
Key: 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
Key: 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
Key: region
Region to select data to compare from....(not implemented)
Key: out
Output image. It consists of 7 planes; the meaning of the first 3
depend on the method used. (1) the first two planes are blank, the
third is the col. den. 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.
Key: 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 also is a cutoff for values of temp > 1000 K, v > 100 km/s.
Additionally, values for column densities greater than 1.0e+27 are not
written to the output file.
Key: b1
Value of B (in GHz) for the optically thick isotope.Default=57.6 (12CO).
Key: b2
Value of B (in GHz) for the optically thin isotope.Default=55.1 (13CO).
Key: j1
the rotational number of the upper level. Default J=1
Key: j2
the rotational number of the upper level. Default J=2
Key: mu
The dipole moment of the molecule (in Debye). Default mu=0.112 (CO)
Key: scale1
A constant that will multiply the peak temperatures in in1.
Default=1.0
Key: scale2
A constant that will multiply the peak temperatures in in2.
Default=1.0
Key: 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).
Key: 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.
Key: options
taulog: the optical depths are written as logs
collog: the column densities are written as logs
maslog: the masses are written as logs