Equivalent Width

Andy Wilson

Hi Andrew,

I’ve also been automating equivalent width calculations recently. I suspect you will take a different approach to me, but I thought I’d share my experience.

I am trying to measure the EW of lots of lines in lots of spectra automatically. I’ve not gone down the path of fitting polynomials or Gaussians. Instead:

  1. Work out the local continuum.
  2. Sum up the flux from the spectrum between 2 predetermined wavelengths for the start and end of the line.
  3. Calculate a dummy flux based on my local continuum level between the 2 wavelengths.
  4. Calculate my absorption flux by subtracting the summed flux from my dummy flux
  5. Finally calculate a width based on this absorption flux and the height of my local continuum.

As in the other posts, I also find working out the local continuum level to be the tricky bit. To deal with varying levels of noise, I take the median continuum of a few wavelength bins either side of my start and end line wavelength, then take the average of the continuum at my start and end wavelengths.

That is an interesting paper, I’ll have to give it a read.