<p>I have H alpha spectra of H II regions in our galaxy. In the paper, the x-axis is in units of km/s and the corresponding line width as well. From this, how can I get equivalent width of the H alpha line?</p>

CC BY-SA 4.0
2020-11-15T21:58:11.393Z
$v = c\Delta \lambda/\lambda_0$
ProfRob
CC BY-SA 4.0
2020-11-17T03:39:03.887Z
It would be much better if you mentioned and linked to the paper and gave the actual value of the line width in km/s. The comment above works to first order, but if it's really wide the answer could turn out to be more interesting!
uhoh
CC BY-SA 4.0
2020-11-17T16:20:30.840Z
@uhoh- Thank You for replying. The link for the paper I am looking at is [link](http://adsabs.harvard.edu/full/1990AJ.....99..622F). I needed to know the H alpha equivalent width of the H2 regions in units of wavelength. Am I missing something here?
user1796
<galaxy><spectra><hydrogen>
How to convert between spectra given in terms of velocity (km/s) to wavelength spectra?
user1796
# How to convert between spectra given in terms of velocity (km/s) to wavelength spectra?

(Asked by: username_0 on 2020-11-15)

I have H alpha spectra of H II regions in our galaxy. In the paper, the x-axis is in units of km/s and the corresponding line width as well. From this, how can I get equivalent width of the H alpha line?

**Tags:** galaxy, spectra, hydrogen
> **Comments:**
> **username_1**: $v = c\Delta \lambda/\lambda_0$  
> **username_2**: It would be much better if you mentioned and linked to the paper and gave the actual value of the line width in km/s. The comment above works to first order, but if it's really wide the answer could turn out to be more interesting!  
> **username_0**: @uhoh- Thank You for replying. The link for the paper I am looking at is [link](http://adsabs.harvard.edu/full/1990AJ.....99..622F). I needed to know the H alpha equivalent width of the H2 regions in units of wavelength. Am I missing something here?  

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## 0 answers

