<p>If you <em>also</em> have photometry, then there is a reasonably accurate conversion between the apparent magnitude and the continuum flux (per unit wavelength interval) at the wavelength of the photometry.</p>
<p>Once you have this conversion factor, you multiply your equivalent width by it to get a flux. To turn that into a luminosity then requires a distance and luminosity is flux multiplied by <span class="math-container">$4\pi d^2$</span>, assuming there is no extinction.</p>

CC BY-SA 4.0
2015-11-25T18:48:18.720Z
2023-01-18T20:59:14.537Z
2023-01-18T20:59:14.537Z
ProfRob
<p>I have a set of equivalent width measurements for different emission lines. How can I use them in order to determine the corresponding line luminosities?</p>

CC BY-SA 3.0
2015-11-25T12:32:32.453Z
The EW gives you only the ratio between line and continuum luminosities. You cannot get the absolute luminosity from that information alone.
pela
<observational-astronomy><star><spectroscopy>
How can I determine line luminosities from equivalent width measurements?
user9879
# How can I determine line luminosities from equivalent width measurements?

(Asked by: username_0 on 2015-11-25)

I have a set of equivalent width measurements for different emission lines. How can I use them in order to determine the corresponding line luminosities?

**Tags:** observational-astronomy, star, spectroscopy

> **Comments:**
> **username_1**: The EW gives you only the ratio between line and continuum luminosities. You cannot get the absolute luminosity from that information alone.  

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## 1 answers

### Answer by username_2 on 2015-11-25. Score: 3

If you *also* have photometry, then there is a reasonably accurate conversion between the apparent magnitude and the continuum flux (per unit wavelength interval) at the wavelength of the photometry.

Once you have this conversion factor, you multiply your equivalent width by it to get a flux. To turn that into a luminosity then requires a distance and luminosity is flux multiplied by $4\pi d^2$, assuming there is no extinction.


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