<p>Reddening does not change the details of the spectrum of a star. The differences in absorption lines that are present in a hot star vs a cool star are still there after reddening. So if you have a spectrum then distinguishing the two scenarios is easy.</p>

<p>If you don't have a spectrum but have two colours then it is still possible to distinguish the scenarios by tracing the star back along an extinction vector in a colour 1 vs colour 2 diagram until it intercepts an intrinsic locus for (e.g.) main sequence stars. This can be definitive, but can be ambiguous depending on the types of star and particular colours.</p>

<p>If you just have a colour, you can't tell.</p>

CC BY-SA 4.0
2019-04-24T21:55:32.697Z
2019-04-24T21:55:32.697Z
ProfRob
<p>How do astronomers distinguish hot stars, reddened by the interstellar light absorption, from the actual cold 
red stars?</p>

<observational-astronomy><extinction>
Difference in observing hot stars that have been reddened and stars that are cool and red
Danish 
# Difference in observing hot stars that have been reddened and stars that are cool and red

(Asked by: username_0 on 2019-04-24)

How do astronomers distinguish hot stars, reddened by the interstellar light absorption, from the actual cold
red stars?

**Tags:** observational-astronomy, extinction

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## 1 answers

### Answer by username_1 on 2019-04-24. Score: 3

Reddening does not change the details of the spectrum of a star. The differences in absorption lines that are present in a hot star vs a cool star are still there after reddening. So if you have a spectrum then distinguishing the two scenarios is easy.

If you don't have a spectrum but have two colours then it is still possible to distinguish the scenarios by tracing the star back along an extinction vector in a colour 1 vs colour 2 diagram until it intercepts an intrinsic locus for (e.g.) main sequence stars. This can be definitive, but can be ambiguous depending on the types of star and particular colours.

If you just have a colour, you can't tell.


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