<p>So lately I've read Intro to stellar winds (particularly chapter 7 Dust-driven winds) by Lamers &amp; cassinelli, I forget how many times I've read this but I still don't really understand. So in the book, it says</p>
<p>&quot;The survivability of a test grain is most easily determined by deriving its radiative equilibrium temperature. If this exceeds the ‘<strong>condensation temperature</strong>’ then the grain will be so hot that it will <strong>sublimate</strong> rather than grow. &quot;</p>
<p>I just still cannot imagine this sentence, because in my mind I think <strong>condensation</strong> is a phase transition from gas to liquid, and <strong>sublimate</strong> is when you have solid thing change to gas.</p>
<p>So the main question is (1)<strong>why if the grain/dust exceed the condensation it will sublimate</strong> ?</p>
<p>another question is, (2) what happen in condensation region ? I mean if condensation is when we have gas change to liquid, then why dust/grain formed in this region ? <strong>aren't these grain/dust a solid</strong> ?</p>
<p>I don't know if I missed some explanation from the book, but any help will be very helpful for me, thank you.</p>

CC BY-SA 4.0
2022-11-07T18:47:26.823Z
Pressures in space are too low to form liquids. The only phase transition possible is between gas and solid. Whether you call the temperature at which this happens "condensation temperature" or "sublimation temperature" is the same thing, it might just indicate the direction of the transition.
AtmosphericPrisonEscape
CC BY-SA 4.0
2022-11-07T21:03:00.157Z
That's basically an answer, @AtmosphericPrisonEscape. It's the same with the "melting point". Water freezes if it is cooled to/below the melting point. You can also use the term "freezing point" and "sublimation temperature".
pela
CC BY-SA 4.0
2022-11-07T23:32:28.620Z
@pela Hmm a partial answer I feel. I also think I should know under which conditions the dust is actually heating the gas efficiently enough to drive a wind, but I don't (although I have Lamers&Casinelli laying around here somewhere..). So given my ignorance of the actual topic, I'll refrain putting that as answer for now.
AtmosphericPrisonEscape
CC BY-SA 4.0
2022-11-08T12:38:43.120Z
I don't have the time to write a formal answer at the moment, but I think your uncertainty is mainly semantical. Like e.g. mist in a humid atmosphere, the formation and destruction of dust grains the interstellar medium is given by an equilibrium that depends on the temperature, densities, radiation field, turbulence, etc. You might benefit from looking into resources like [Jones 05](https://ui.adsabs.harvard.edu/abs/2005ESASP.577..239J), [Cox 05](https://ui.adsabs.harvard.edu/abs/2005ARA%26A..43..337C), or [Jones & Nuth 11](https://ui.adsabs.harvard.edu/abs/2011A%26A...530A..44J).
pela
<astrophysics><stellar-evolution><stellar-astrophysics><solar-wind>
The necessary conditions for driving winds with dust (Dust-driven Wind)
aapnegara
# The necessary conditions for driving winds with dust (Dust-driven Wind)

(Asked by: username_0 on 2022-11-07)

So lately I've read Intro to stellar winds (particularly chapter 7 Dust-driven winds) by Lamers & cassinelli, I forget how many times I've read this but I still don't really understand. So in the book, it says

"The survivability of a test grain is most easily determined by deriving its radiative equilibrium temperature. If this exceeds the ‘**condensation temperature**’ then the grain will be so hot that it will **sublimate** rather than grow. "

I just still cannot imagine this sentence, because in my mind I think **condensation** is a phase transition from gas to liquid, and **sublimate** is when you have solid thing change to gas.

So the main question is (1)**why if the grain/dust exceed the condensation it will sublimate** ?

another question is, (2) what happen in condensation region ? I mean if condensation is when we have gas change to liquid, then why dust/grain formed in this region ? **aren't these grain/dust a solid** ?

I don't know if I missed some explanation from the book, but any help will be very helpful for me, thank you.

**Tags:** astrophysics, stellar-evolution, stellar-astrophysics, solar-wind

> **Comments:**
> **username_1**: Pressures in space are too low to form liquids. The only phase transition possible is between gas and solid. Whether you call the temperature at which this happens "condensation temperature" or "sublimation temperature" is the same thing, it might just indicate the direction of the transition.  
> **username_2**: That's basically an answer, @username_1. It's the same with the "melting point". Water freezes if it is cooled to/below the melting point. You can also use the term "freezing point" and "sublimation temperature".  
> **username_1**: @username_2 Hmm a partial answer I feel. I also think I should know under which conditions the dust is actually heating the gas efficiently enough to drive a wind, but I don't (although I have Lamers&Casinelli laying around here somewhere..). So given my ignorance of the actual topic, I'll refrain putting that as answer for now.  
> **username_2**: I don't have the time to write a formal answer at the moment, but I think your uncertainty is mainly semantical. Like e.g. mist in a humid atmosphere, the formation and destruction of dust grains the interstellar medium is given by an equilibrium that depends on the temperature, densities, radiation field, turbulence, etc. You might benefit from looking into resources like [Jones 05](https://ui.adsabs.harvard.edu/abs/2005ESASP.577..239J), [Cox 05](https://ui.adsabs.harvard.edu/abs/2005ARA%26A..43..337C), or [Jones & Nuth 11](https://ui.adsabs.harvard.edu/abs/2011A%26A...530A..44J).  

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