<blockquote>
<p>...how typical is the solar corona?</p>
</blockquote>
<p>The Sun is remarkably &quot;average&quot; (e.g., see <a href="https://physics.stackexchange.com/a/262732/59023">https://physics.stackexchange.com/a/262732/59023</a>).  So my best guess is that the corona is also remarkably &quot;average.&quot;  Technically the most abundant stars are red dwarfs and the Sun is a yellow dwarf, but dwarf stars are the most abundant and the sun is part of the main sequence line of stars.</p>
<blockquote>
<p>Is there any rule of thumb for the average dimensions of the corona, possibly depending on the mass of or other parameters of the star? Is it possible to estimate to at least an order of magnitude how thick a shell around a star would be which would be most likely be filled with plasma?</p>
</blockquote>
<p>This is tricky because the <a href="https://en.wikipedia.org/wiki/Stellar_corona" rel="nofollow noreferrer">corona</a> actually stops at the <a href="https://en.wikipedia.org/wiki/Heliosphere#Termination_shock" rel="nofollow noreferrer">termination shock</a> of the <a href="https://en.wikipedia.org/wiki/Heliosphere" rel="nofollow noreferrer">heliosphere</a>.  The size and shape of the Sun's region of influence in the <a href="https://en.wikipedia.org/wiki/Interstellar_medium" rel="nofollow noreferrer">interstellar medium (ISM)</a> depends upon the strength/speed of the <a href="https://en.wikipedia.org/wiki/Solar_wind" rel="nofollow noreferrer">solar wind</a> and the properties of the ISM.  This would be true of all astrospheres.  The location of the associated termination shocks would be determined largely by a balance of hydrodynamic and magnetic forces (much more heavily weighted toward the former than latter in many cases).</p>
<blockquote>
<p>What are the main constituents of the coronal plasma?</p>
</blockquote>
<p>The main particle species (order of particle number density from largest to smallest) are electrons, protons, and alpha-particles.  Beyond alpha-particles, the number densities drop exponentially with CNO constituents plus sulphur and silicon picking up the tail.  Iron is present as well, but in much lower amounts.  I have provided some references in the following answer:  <a href="https://astronomy.stackexchange.com/a/17899/13663">https://astronomy.stackexchange.com/a/17899/13663</a>.</p>
<blockquote>
<p>If I intend to model the corona as an homogenous shell (which definitely is a strong assumption), what are the ranges of the number densities of the abundant particles?</p>
</blockquote>
<p>You need to be a little more specific.  At what altitude do you intend to model the corona?  The number density varies with altitude.  The paper by <a href="https://doi.org/10.1088/2041-8205/736/1/L17" rel="nofollow noreferrer"><em>Gopalswamy and Yashiro</em> [2011]</a> discusses some simplified number density models that vary with radial distance, for instance.  I would also glance at the references therein to see some examples of other coronal number density models.</p>
<p>In general, the corona and solar wind are comprised of ~95% protons, ~4% alpha-particles, and the remaining ~1% contains all the heavier ions.  The <a href="https://en.wikipedia.org/wiki/Plasma_(physics)" rel="nofollow noreferrer">plasma</a> is quasi-neutral so the total electron number density will satisfy:
<span class="math-container">$$
n_{e} = \sum_{s} \ Z_{s} \ n_{s}
$$</span>
where <span class="math-container">$Z_{s}$</span> is the charge state of species <span class="math-container">$s$</span> and <span class="math-container">$n_{s}$</span> is the number density of species <span class="math-container">$s$</span>.</p>

CC BY-SA 4.0
2021-08-31T14:42:36.377Z
2021-08-31T14:42:36.377Z
honeste_vivere
<p>I am after the basic physical properties of the corona of a star, here some questions for which I would like to have an answer, even only for a subset of them:</p>
<ol>
<li>I know some things about the corona of our sun, but <strong>how typical is the solar corona?</strong></li>
<li>Is there any rule of thumb for the <strong>average dimensions of the corona</strong>, possibly depending on the mass of or other parameters of the star? Is it possible to estimate to at least an order of magnitude how thick a shell around a star would be which would be most likely be filled with plasma?</li>
<li>What are the main constituents of the coronal plasma?</li>
<li>If I intend to model the corona as an homogenous shell (which definitely is a strong assumption), <strong>what are the ranges of the number densities of the abundant particles?</strong></li>
</ol>
<h3>Related</h3>
<ul>
<li><a href="https://astronomy.stackexchange.com/questions/28139/in-the-closest-stars-can-you-see-the-stellar-corona">In the closest stars, can you see the stellar corona?</a></li>
<li><a href="https://astronomy.stackexchange.com/questions/35520/what-is-the-dielectric-constant-of-a-star">What is the dielectric constant of a star?</a></li>
</ul>

<star><the-sun><solar-flare><coronal-mass-ejection><corona>
Physical properties of the stellar corona?
B--rian
# Physical properties of the stellar corona?

(Asked by: username_0 on 2021-04-16)

I am after the basic physical properties of the corona of a star, here some questions for which I would like to have an answer, even only for a subset of them:

1. I know some things about the corona of our sun, but **how typical is the solar corona?**
2. Is there any rule of thumb for the **average dimensions of the corona**, possibly depending on the mass of or other parameters of the star? Is it possible to estimate to at least an order of magnitude how thick a shell around a star would be which would be most likely be filled with plasma?
3. What are the main constituents of the coronal plasma?
4. If I intend to model the corona as an homogenous shell (which definitely is a strong assumption), **what are the ranges of the number densities of the abundant particles?**

### Related

* [In the closest stars, can you see the stellar corona?](https://astronomy.stackexchange.com/questions/28139/in-the-closest-stars-can-you-see-the-stellar-corona)
* [What is the dielectric constant of a star?](https://astronomy.stackexchange.com/questions/35520/what-is-the-dielectric-constant-of-a-star)

**Tags:** star, the-sun, solar-flare, coronal-mass-ejection, corona

---

## 1 answers

### Answer by username_1 on 2021-08-31. Score: 2

> ...how typical is the solar corona?

The Sun is remarkably "average" (e.g., see <https://physics.stackexchange.com/a/262732/59023>). So my best guess is that the corona is also remarkably "average." Technically the most abundant stars are red dwarfs and the Sun is a yellow dwarf, but dwarf stars are the most abundant and the sun is part of the main sequence line of stars.

> Is there any rule of thumb for the average dimensions of the corona, possibly depending on the mass of or other parameters of the star? Is it possible to estimate to at least an order of magnitude how thick a shell around a star would be which would be most likely be filled with plasma?

This is tricky because the [corona](https://en.wikipedia.org/wiki/Stellar_corona) actually stops at the [termination shock](https://en.wikipedia.org/wiki/Heliosphere#Termination_shock) of the [heliosphere](https://en.wikipedia.org/wiki/Heliosphere). The size and shape of the Sun's region of influence in the [interstellar medium (ISM)](https://en.wikipedia.org/wiki/Interstellar_medium) depends upon the strength/speed of the [solar wind](https://en.wikipedia.org/wiki/Solar_wind) and the properties of the ISM. This would be true of all astrospheres. The location of the associated termination shocks would be determined largely by a balance of hydrodynamic and magnetic forces (much more heavily weighted toward the former than latter in many cases).

> What are the main constituents of the coronal plasma?

The main particle species (order of particle number density from largest to smallest) are electrons, protons, and alpha-particles. Beyond alpha-particles, the number densities drop exponentially with CNO constituents plus sulphur and silicon picking up the tail. Iron is present as well, but in much lower amounts. I have provided some references in the following answer: <https://astronomy.stackexchange.com/a/17899/13663>.

> If I intend to model the corona as an homogenous shell (which definitely is a strong assumption), what are the ranges of the number densities of the abundant particles?

You need to be a little more specific. At what altitude do you intend to model the corona? The number density varies with altitude. The paper by [*Gopalswamy and Yashiro* [2011]](https://doi.org/10.1088/2041-8205/736/1/L17) discusses some simplified number density models that vary with radial distance, for instance. I would also glance at the references therein to see some examples of other coronal number density models.

In general, the corona and solar wind are comprised of ~95% protons, ~4% alpha-particles, and the remaining ~1% contains all the heavier ions. The [plasma](https://en.wikipedia.org/wiki/Plasma_(physics)) is quasi-neutral so the total electron number density will satisfy:
$$
n\_{e} = \sum\_{s} \ Z\_{s} \ n\_{s}
$$
where $Z\_{s}$ is the charge state of species $s$ and $n\_{s}$ is the number density of species $s$.


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