<p>I'm looking for an explanation of the cepheid mechanism. I looked all over the web but, strangely, I found nothing on it (almost nothing).</p>
<p>For the moment, here is what I got :</p>
<blockquote>
<p>The theory progressed over the last century, from a binary star system (2 suns rotating around the same gravity point) to a specific matter composition...</p>
</blockquote>
<p>The pulsation rests on the Helium ionization (the transparent He2 gas will turn into He3, which is an opaque gas). Step by step we can resume here :</p>
<p><strong>1]</strong> The Helium layer is condensed by the gravitation force. Here the temperature increases but, overall, it's the density that increases. This transforms the He2 to He3 (the star becomes opaque)</p>
<p><strong>2]</strong> According to Kramer's opacity laws, the opacity is proportional to the density on the temperature. As the density increased quicker than the temperature, the new He3 gaz became opaque.</p>
<p><strong>3]</strong> The opaque gas keeps the heat to itself and it takes more and more place</p>
<p><strong>4]</strong> This expansion of matter cools down the gas and the He3 turns into He2.</p>
<p><strong>5]</strong> The light goes how and we cycle begins again.</p>
<p><strong>The same explanation in a few words is :</strong></p>
<p><code>Concentration of He2 + Temperature = He3 + Opacity</code></p>
<p><code>Opacity = Keep the heat</code></p>
<p><code>Heater = Take more space</code></p>
<p><code>Take more space/Expansion = Cooling down</code></p>
<p><code>Cooling down + He3 = He2 + Transparent layer</code></p>
<p><code>And it starts again...</code></p>
<p>But I'm not confident in my explanation and questions are still remaining. For instance :</p>
<p><em>Is my summary good? Did I make mistakes?
Does He3 have a bigger density than He2?
Why the star can't reach a balance point?
Is the temperature or the pressure that allows the transformation of He2 to He3?</em></p>
<p>In a nutshell I ask you to enlighten me and show me my errors (I'm still surprised that no one ever spoke of that topic...)</p>
<p><strong>My Sources :</strong></p>
<p>The Secret lives of cepheid - Section Cepheid Pulsation Mechanism ( <a href="https://arxiv.org/pdf/1504.02713" rel="nofollow noreferrer">https://arxiv.org/pdf/1504.02713</a> )
The Wikipedia articles in All langages translated in English (the best are : <a href="https://uk.wikipedia.org/wiki/%D0%A6%D0%B5%D1%84%D0%B5%D1%97%D0%B4%D0%B0" rel="nofollow noreferrer">https://uk.wikipedia.org/wiki/%D0%A6%D0%B5%D1%84%D0%B5%D1%97%D0%B4%D0%B0</a> )</p>
<p>Thanks a lot</p>
<p><em>TAGS : K Kappa Mechanism ; Gamma Mechanism ; Eddington Valve ; Cepheid</em></p>

CC BY-SA 4.0
2024-05-10T16:16:57.580Z
https://en.wikipedia.org/wiki/Cepheid_variable#Pulsation_model https://www.astro.princeton.edu/~gk/A403/pulse.pdf https://www.astronomy.ohio-state.edu/ryden.1/ast162_4/notes16.html https://en.wikipedia.org/wiki/Kappa%E2%80%93mechanism https://iopscience.iop.org/book/mono/978-0-7503-5794-4/chapter/bk978-0-7503-5794-4ch20 https://ned.ipac.caltech.edu/level5/ESSAYS/Evans/evans.html
ProfRob
CC BY-SA 4.0
2024-05-10T16:21:37.873Z
Just the first few hits from googling "Cepheid pulsation mechanism"
ProfRob
CC BY-SA 4.0
2024-05-10T16:31:25.543Z
Found that to explain the story of the Cepheid mechanism theory (https://app.aavso.org/media/jaavso/2739.pdf) 
I will check your articles, thanks!
BiMathAx STUDIO
CC BY-SA 4.0
2024-05-10T16:54:14.207Z
https://youtu.be/X_3QAB3o4Vw (I found a video of the subject, that strange because I didn't find it with my navigator; I needed to switch of app...)
BiMathAx STUDIO
<cepheids><eddington-luminosity>
Why does Cepheid Brightness change?
BiMathAx STUDIO
# Why does Cepheid Brightness change?

(Asked by: username_0 on 2024-05-10)

I'm looking for an explanation of the cepheid mechanism. I looked all over the web but, strangely, I found nothing on it (almost nothing).

For the moment, here is what I got :

> The theory progressed over the last century, from a binary star system (2 suns rotating around the same gravity point) to a specific matter composition...

The pulsation rests on the Helium ionization (the transparent He2 gas will turn into He3, which is an opaque gas). Step by step we can resume here :

**1]** The Helium layer is condensed by the gravitation force. Here the temperature increases but, overall, it's the density that increases. This transforms the He2 to He3 (the star becomes opaque)

**2]** According to Kramer's opacity laws, the opacity is proportional to the density on the temperature. As the density increased quicker than the temperature, the new He3 gaz became opaque.

**3]** The opaque gas keeps the heat to itself and it takes more and more place

**4]** This expansion of matter cools down the gas and the He3 turns into He2.

**5]** The light goes how and we cycle begins again.

**The same explanation in a few words is :**

`Concentration of He2 + Temperature = He3 + Opacity`

`Opacity = Keep the heat`

`Heater = Take more space`

`Take more space/Expansion = Cooling down`

`Cooling down + He3 = He2 + Transparent layer`

`And it starts again...`

But I'm not confident in my explanation and questions are still remaining. For instance :

*Is my summary good? Did I make mistakes?
Does He3 have a bigger density than He2?
Why the star can't reach a balance point?
Is the temperature or the pressure that allows the transformation of He2 to He3?*

In a nutshell I ask you to enlighten me and show me my errors (I'm still surprised that no one ever spoke of that topic...)

**My Sources :**

The Secret lives of cepheid - Section Cepheid Pulsation Mechanism ( <https://arxiv.org/pdf/1504.02713> )
The Wikipedia articles in All langages translated in English (the best are : <https://uk.wikipedia.org/wiki/%D0%A6%D0%B5%D1%84%D0%B5%D1%97%D0%B4%D0%B0> )

Thanks a lot

*TAGS : K Kappa Mechanism ; Gamma Mechanism ; Eddington Valve ; Cepheid*

**Tags:** cepheids, eddington-luminosity

> **Comments:**
> **username_1**: https://en.wikipedia.org/wiki/Cepheid_variable#Pulsation_model https://www.astro.princeton.edu/~gk/A403/pulse.pdf https://www.astronomy.ohio-state.edu/ryden.1/ast162_4/notes16.html https://en.wikipedia.org/wiki/Kappa%E2%80%93mechanism https://iopscience.iop.org/book/mono/978-0-7503-5794-4/chapter/bk978-0-7503-5794-4ch20 https://ned.ipac.caltech.edu/level5/ESSAYS/Evans/evans.html  
> **username_1**: Just the first few hits from googling "Cepheid pulsation mechanism"  
> **username_0**: Found that to explain the story of the Cepheid mechanism theory (https://app.aavso.org/media/jaavso/2739.pdf)  I will check your articles, thanks!  
> **username_0**: https://youtu.be/X_3QAB3o4Vw (I found a video of the subject, that strange because I didn't find it with my navigator; I needed to switch of app...)  

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## 0 answers

