# What does "EW(Hα)" mean?

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

Does anybody know what "EW" means?

Thanks.

"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, but for future readers, the formula would be nice :)
– pela
Apr 20 '16 at 8:59
• I agree with you, @pela. It would be nice to have a formula to back it up. May 3 at 16:48