Questions tagged [stellar-atmospheres]
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14
questions
19
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2answers
3k views
Can lightning occur in stars like the Sun?
In the Wikipedia article about lightining, the following explanation is given about the electrification process in clouds:
The details of the charging process are still being studied by
scientists, ...
2
votes
0answers
91 views
Why are helium resonance lines called “resonance lines”?
Examples of the use of the term:
Formation of the helium extreme-UV resonance lines
On the Formation of the Resonance Lines of Helium in the Sun (unpaywalled)
Formation of the helium EUV resonance ...
8
votes
2answers
414 views
What does this “web on the surface of the Sun” image reflect? What does 789 nm show us?
What is this web on the surface of the Sun? has got me thinking.
This is probably not a normal color photo.
The cooler areas are really dark!
update: Comments point out
The NSO press release says ...
2
votes
2answers
48 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 ...
4
votes
1answer
306 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
votes
2answers
364 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
votes
1answer
625 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
53 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
700 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 ...
13
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 ...
10
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
99 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?
12
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2answers
5k 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
414 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 ...
