- automated line fitting algorithm
rapidly fits emission line spectra, using a genetic algorithm to
optimise fitting parameters. It is intended to be entirely automated, but
while the default values should work well in many situations, a good fit to
your observed spectrum may require some adjustments to the input parameters.
It is optimised for optical spectra, but can be applied to any wavelength
range if a suitable line catalogue is provided.
reads one dimensional spectra in either plain text or FITS format.
Plain text input should consist of two columns, giving wavelength and flux. It
can also read data cubes and row-stacked spectra in FITS format. Results are
written out in plain text, to files containing the fit (total fit,
continuum-subtracted original, continuum, sky lines and residuals), and the
line flux measurements.
- -b, --bad-data [REAL]
- If all values in a spectrum are below the value specified,
alfa will not fit it. Most useful for avoiding wasting time on low
signal regions of data cubes.
- Prints out the bibliographic details of the paper to cite
if you use alfa in your research.
- -g, --generations [INTEGER]
- The number of generations used in the genetic algorithm.
- -n, --normalise [VALUE]
- Normalise to Hb=100 assuming that F(Hb)=VALUE. If
VALUE is zero, no normalisation is applied. If this option is not
specified, fluxes are normalised using the measured value of Hb if it is
detected, and not normalised otherwise.
- -o, --output-dir [DIRECTORY]
- The directory in which to put the output files. Default:
current working directory.
- -pr, --pressure [REAL]
- The fraction of the population retained from each
generation. The product of the pressure and the population size should be
an integer. Default: 0.3
- -ps, --populationsize [INTEGER]
- The size of the population used in the genetic algorithm.
- -rg, --resolution-guess [VALUE]
- Initial guess for the resolution [lambda/delta lambda].
Default: estimated using the sampling of the input spectrum, assuming that
it is Nyquist sampled.
- -rtol1, --resolution-tolerance-1 [VALUE]
- Variation allowed in resolution in first pass. Default:
equal to 0.9 x resolution guess.
- -rtol2, --resolution-tolerance-2 [VALUE]
- Variation allowed in resolution in second pass. Default:
- -skycat, -strongcat, -deepcat [FILENAME]
- The files containing the line catalogues to be used for the
removal of sky lines, the estimation of velocity and resolution, and the
full line fitting. The default catalogues are stored in /usr/share/alfa .
If you wish to create your own catalogue, the required format is that each
line should be 85 characters wide, with a wavelength in the first column,
and the rest of the characters are not used by the code but are
transferred to the output files. They can thus be used, as in the supplied
catalogues, for line transition data.
- -ss, --subtract-sky
- Fit and subtract night sky emission lines before fitting
nebular emission lines.
- -ul, --upper-limits
- Write out upper limits for all lines searched for and not
- -vg, --velocity-guess [VALUE]
- Initial guess for the velocity of the object [km/s].
- -vtol1, --velocity-tolerance-1 [VALUE]
- Variation allowed in velocity in first pass of the fitting.
- -vtol2, --velocity-tolerance-2 [VALUE]
- Variation allowed in velocity in second pass of the
fitting. Default: 60km/s
No known bugs.