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
        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.

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 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.

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