NAME · USAGE · PARAMETERS · DESCRIPTION · SEE_ALSO
eqwidths -- Equivalent widths
eqwidths spectra bands output
- spectra
- List of input spectra. It can be any file template.
The input spectra should be dispersion corrected, and optionally flux
calibrated.
- bands
- List of wavelength bandpasses. This is a six column text file with the
red, line, and blue bandpass specification. Each bandpass is specified by
the center wavelength and a width. The red and blue bandpasses are used to
compute the continuum level at the line by using a linear interpolation.
- output
- Output text file.
- radial = ""
- List of radial velocities for input spectra in Kilometers per second.
There is a one to one correspondence between the input spectra and the
radial velocities specified in this file, but it is not required that
the number of radial velocities be the same as the number of input spectra.
If the radial velocity list is shorter than the input list then no correction
is assumed for the remaining spectra in the input list.
- interpolation = "linear"
- Pixel interpolation mode. This parameter specifies which method is
used to interpolate fractional pixel values.
Possible values are nearest
, linear
, poly3
, poly5
,
and spline3
, for nearest neighbor, linear interpolation, third order
polynomial, fifth order polynomial, and cubic spline, respectively.
- start = "W0"
- Starting wavelength keyword name. The named keyword is used to get the
starting wavelength from the image headers.
- delta = "WPC"
- Wavelength increment keyword name. The named keyword is used to get the
wavelength per pixel from the image headers.
- dispersion = "DC-FLAG"
- Wavelength correction flag keyword name. The named keyword is used to know
if the image has been dispersion corrected or not.
- flux = "CA-FLAG"
- Flux calibration flag keyword name. The named keyword is used to know
if the image has been flux calibrated or not.
For each spectrum in the input list the task computes the equivalent widths
for a list of bandpasses. Optionally a list of radial velocties may be
supplied for each one of the spectrum in the input list.
For each line bandpass the task computes the flux for the corresponding red
and blue bandpasses, and using these values it computes the continuum level
for the line bandpass by using a linear interpolation. This value is then
substracted from the line, and then the flux for the line is computed.
The line flux is multiplied by the wavelength per pixel value if the spectrum
is flux calibrated. Finally, the equivalent width is determined from the line
flux, and the interpolation coefficients for the continuum, by using the
following formulae:
equivalent width = line flux / (a * line wavelength + b),
where
continuum = a * wavelength + b
The "a" and "b" are coefficients are determined from a linear interpolation
by using the red and blue bandpass fluxes.
The equivalent withs will be always positive for absorption lines and
negative for emission lines, assuming that the fluxes in the red and
blue bandpasses are positive (i.e. positive continuum level).
If the list of radial velocities is specified then each wavelength in the
list of bandpasses (laboratory system) is corrected acording with the
following formulae:
lambda observed = lambda laboratory * (1 + z)
where
1 + z = sqrt ((c + v) / (c - v))
The output of the task is a six column table, with the following data: the
bandpass wavelength, bandpass width, bandpass wavelength after radial velocity
correction, continuum level at the line bandpass, line flux, and equivalent
width. The image name is printed at the begining of the bandpass list along
with a title line.
onedspec.splot
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This file last updated on 5 Nov 1993