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Basic Information on mbspect
Purpose: Make spectrum and measure velocities from a Miriad image.
Categories: image analysis and display.
MBSPECT makes an spectrum of the velocity or frequency axis of a
Miriad image. The spectrum is integrated, averaged or beam-weighted,
over the width specified, for the other image axes. Robust spectral
baselines can be fitted, and the profile parameterised (velocities,
widths, moments). The output spectrum can be plotted and/or written
out as a miriad and/or ascii file for further analysis.
The input image. vxy and xyv images are acceptable inputs.
The output spectrum, if required. Spectral units are always in the
same units as the input file (even if a conversion is performed for
the plot and/or log file). This spectrum can be read back into
The position, in world coordinates, for which the spectrum is
required, e.g. coord=12:00:13,-42:00:43. The cube must have
an RA and a DEC axis. The pixel with the nearest position is
chosen. The default is the centre of the image (not necessarily
the reference pixel).
Two numbers, being the spatial width of the box in pixels (in RA
and DEC) within which the spectrum is averaged (or integrated).
Must be odd numbers. Default is 1,1.
The x-axis can be plotted as 'channel', 'frequency' ('FREQ'),
'optical' velocity ('FELO'), 'radio' velocity ('VELO'), or the units
in the image. The default which is whatever units are in the header.
If 'average' then the pixels enclosed in the x-y area specified
are averaged. If 'sum' they are summed and normalized if the units
are known. If 'point' they are optimally weighted according to
the beam parameters, assuming that the source is unresolved.
Default is 'average'
X-axis range for plot. The default is to self-scale to the region
requested. The units are km/s for velocity and MHz for frequency
(i.e. not the normal miriad convention).
Y-axis range for plot. The default is to self-scale.
Hanning smoothing length (an odd integer < 15). The default is
no smoothing (hann = 1).
Order of optional robust (clipped polynomial) fit (0-10) to be applied
to the spectral axis. If the order is positive (0 to 10), the fit is
plotted on top of the data; if negative (-0 to -10), the fit is
subtracted before plotting. The fit is always subtracted from any
output data written. (For bulk removal of baselines in a cube, use
contsub). Default is no fit.
List of minimum match task enrichment options.
1deriv Take 1-sided derivative of spectrum before plotting
and after Hanning smoothing. Useful for Zeeman enthusiasts.
2deriv Take 2-sided derivative of spectrum before plotting.
histo Plot the spectrum as a histogram instead of joining points.
pstyle1 Alternative plot style, where the object and position
information is omitted and the comment field is centered
at the top of the plot. Typically, this is used for
publication-quality plots (the source name, if required.
should be inserted into the comment field).
pstyle2 Alternative plot style, where the object and position
information is omitted, the comment field is centered
at the top of the plot (as with options=pstyle1), and
the x and y axis labels are omitted. Typically, this is
used to generate publication-quality n x m matrix plots
(the source name, if required should be inserted into
the comment field).
posfit If width>1, a source position is estimated from a Gaussian
fit to the moment map. The moment map is formed using the
velocity range specified by the profile parameter. If
yaxis=point, this new position is used when forming
the spectrum (the region set by the initial coord
parameter and the width parameter is not changed).
measure Measure various spectral parameters on plotted spectrum.
If a profile window is set, the line is only measured
within this window. If the order keyword is used, the fit
is always subtracted before spectral fitting. If a plot
device is selected, the width-maximised 50% and 20% points
are highlighted with a circle and the width-minimised
points are highlighted with a cross. Zeroth moment (profile
area), first moment (mean velocity/frequency/channel) and
second moment (dispersion) are calculated in the usual way.
These parameters are not robust unless careful use of the
profile and clip parameters is made. However, more
robust moment-like parameters are also calculated by using an
algorithm which minimises the mean absolute deviation of
the flux-weighted velocities
Two values. Exclude pixels with values in the range clip(1) to clip(2).
If only one value is given, then exclude -abs(clip) to abs(clip).
This specifies the x-axis ranges to be excluded from any
continuum fit, e.g. those containing line emission. It consists
of a number of pairs, each pair giving a start and end x-value.
The default is that all channels are line-free, which is quite a
good approximation if the line is weak compared to the continuum.
The units of the x-axis values are the same as given by the xaxis
Two values. This specifies the x-axis range to be included for
profile measurement (options=measure). It consists of a start
and end x-value. The default is that all channels are used for
profile measurement. For weak lines, you will normally need to
set a profile window, a mask window a clip level, or any
combination of the above. The profile and mask windows may be
the same, although the profile window is limited to a single pair
of values. The units of the x-axis values are the same as given
by the xaxis keyword.
Standard PGPLOT device. See the help on device for more information.
Up to 2 values. Character sizes in units of the PGPLOT default
(which is ~ 1/40 of the view surface height) for the plot axis
labels and the title.
Defaults try to choose something sensible. Use 0.0 to default
any particular value.
Write spectrum to this ascii file. Spectral axis units are as
specified by the xaxis keyword. Default is no output file.
A one-line comment which is written into the logfile and any plot.