Documentation 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