Questions tagged [stellar-atmospheres]

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2
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2answers
41 views

What does the opacity of a molecular transition mean?

In particular, what does it mean when a line (e.g, emission line in stellar wind) is optically thick or thin. I know what an optically think/thick medium is, but how does this concept compare to ...
3
votes
1answer
112 views

At what depth below the Sun's surface does the density reach that of water?

I'd like to write a short supplementary answer to A probe floating in Sun's surface but in order to do so I need to know at roughly what depth relative to the Sun's surface the mass density reaches 1 ...
0
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2answers
91 views

What is the density profile within the Sun's photosphere? Which one of these is wrong?

The Sun's photosphere contains the Sun's surface as defined by opacity = 2/3 point. I'd like to see the profile of mass density from bottom to top of the photosphere. I did a quick search and got ...
0
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1answer
168 views

Does the Sun's atmosphere have a scale height?

Much of the Earth's atmosphere has a scale height $h$ of roughly 7 to 8 kilometers such that the local density varies as $\exp(-(r-r_0)/h)$ where r is the radius vector and $r_0$ would be some ...
2
votes
1answer
51 views

What was the “optical illusion” that led to erroneous metal concentrations in stellar atmospheres in the galactic center?

Articles summarizing a recent result about certain heavy element concentrations in stars near the galactic center all say that earlier reports about high levels in stellar atmospheres were the product ...
8
votes
3answers
630 views

Why does Gaia use only calcium NIR lines for stellar radial velocity measurements?

I was reading this overview article about the Gaia spacecraft and I saw the following statement: These spectra provide radial velocity information that are used to study the kinematic and dynamic ...
11
votes
1answer
1k views

How can neutron stars have gaseous atmospheres?

Neutron stars can have small atmospheres. However, they also have extremely strong gravitationally pulls. Shouldn't the all the gas molecules be drawn to the star's surface, and become solids under ...
8
votes
2answers
4k views

What happens to oxygen produced on the Sun (or other stars)?

Through nuclear fusion, the Sun can (or at the very least, someday will) produce atoms of all elements up to and including oxygen. And in terrestrial chemistry at least, when you combine oxygen, ...
1
vote
1answer
97 views

Why do we not find larger quantities of helium in the Sun's atmosphere?

The Sun currently shines because H is being burned to He, and it has been doing this for about 4.57 Ga. But when we analyze the Sun's atmosphere, we do not find unusually large amounts of He. Why not?
11
votes
2answers
4k views

How does one determine the effective temperature of a star from its spectrum?

Determining effective temperature of a star is in general a non-trivial task. Simple reason for this is that we can only study the electromagnetic radiation from a star, but not the temperature ...
8
votes
2answers
370 views

How well can we in principle determine $T_{\textrm{eff}}$ of a star?

This is a question about the basics of astronomy, which I have never happened to see a good discussion for. It is about how well would we be able to measure effective temperature of a star, if we had ...