I came across a website saying that classical T Tauris have an "EW(Hα) > 5 angstroms".

Does anybody know what "EW" means?



1 Answer 1


"EW" stands for Equivalent Width. The equivalent width of a spectral line is essentially the range of continuum one would integrate over to get the same flux as the spectral line.

In your case, this is the Hα line.

  • 1
    $\begingroup$ +1, but for future readers, the formula would be nice :) $\endgroup$
    – pela
    Commented Apr 20, 2016 at 8:59
  • $\begingroup$ I agree with you, @pela. It would be nice to have a formula to back it up. $\endgroup$
    – Questioner
    Commented May 3, 2021 at 16:48

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