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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 a 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 MbSpect.
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'),
'radio' velocity ('VELO'), 'optical' velocity ('FELO'), or the
units in the image. The default is whatever units are in the
header. A second value will overwrite the default label for this
axis. You can use pgplot escape characters to change fonts
and sub/superscript level, e.g.,
'Optical Velocity, \ficz\fr km\u-1s\d' will write 'cz' in
italics and '-1' as a superscript.
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'. A second value will overwrite
the default label for this axis.
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
2deriv Take 2-sided derivative of spectrum before plotting.
histo Plot the spectrum as a histogram instead of joining
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
that minimises the mean absolute deviation of the flux-
minicube If an output file is selected (out parameter selected),
a 3x3 mincube is produced. No extra spatial information
is available; the extra spatial dimensions just
duplicate spectral information in the central pixel.
Useful for tasks such as regrid that only work with
cubes whose dimensions are not unity.
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
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 keyword.
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
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.
Up to 2 values. Line widths for the axes and the plot.
Defaults to 1,1.
Up to 3 values. Colors for the main spectrum, the polynomial
fit and the 'measure' parameters. Defaults to 1,2,3
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. If the comment contains spaces you need to enclose it
in single quotes.
Note that this program does not report its version number so that gif
and ps output can be piped.
Revision: 1.21, 2012/09/03 05:28:06 UTC
Generated by firstname.lastname@example.org on 03 Sep 2012