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hyunxu
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Red dwarf stars are main sequence stars but they have such low mass that they’re much ' cooler' than stars like our Sun.
Then Simple question here : Sun is cool or hot??
Then Simple question here : Sun is cool or hot??
hyunxu said:Then Simple question here : Sun is cool or hot??
Quite differentstefan r said:The terms cool and warm can be ambiguous. Artists, fashion designers and painters would say that "cool" colors have more blue in them. This is the opposite of a star's surface temperature.
hyunxu said:Red dwarf stars are main sequence stars but they have such low mass that they’re much ' cooler' than stars like our Sun.
Then Simple question here : Sun is cool or hot??
Ken G said:... you have stars that are more massive, less convective near the surface, and ultimately have core-collapse supernovae, and stars that are less massive, more convective near the surface, and become white dwarfs...
Their surface temperatures range from 30,000 K to around 200,000 K, hotter than almost all other stars.
Massive main-sequence stars create a very hot core which fuses hydrogen very rapidly via the CNO process and results in strong convection throughout the whole star.
... one of the most massive and most luminous stars known...strongly convective all the way to the core and have dredged up fusion products to the surface
Ken G said:Nevertheless, "cool" and "hot" are not really arbitrary distinctions for stars, they are an effort to notice that stars can be divided into two very different flavors. Of course any such division is artificial, and more divisions can certainly be made, but in a coarse sense you have stars that are more massive, less convective near the surface, and ultimately have core-collapse supernovae, and stars that are less massive, more convective near the surface, and become white dwarfs.
The sun has coronal holes which are not convective. The corona further complicates the hot vs cool question.Ken G said:...it is far from established that all Wolf-Rayet stars have convection zones that reach the surface. Indeed, the surfaces of last scattering in Wolf-Rayet stars tend to be found within a supersonic wind, which is certainly not convective.
Ken G said:But all distinctions are arbitrary, it doesn't make them useless. Most of the stellar astrophysics community is divided into "hot star" and "cool star" studies. Better if everyone went to the same conferences, but then they'd just be too big and varied.
Subfields are generally divided by star type, but astronomers often characterize their expertise by wavelength. It's odd, but you often find "radio astronomers" attending a "cool star meeting", or "X-ray astronomers" attending a "hot star meeting," or vice versa. The lines have historical purposes, but aren't always logical.stefan r said:Are they divided by star types or by telescope/detector type?
Possibly "hot stars," possibly "interstellar medium." If you are interested in the stars that illuminate the nebula, or the history of the supernovae that made it, you might hear about these at a "hot star" meeting. I doubt cool star astronomers care much about the Orion nebula!Would a study of the Orion Nebula go to the "hot star" conference or the fit in with the "cool" astronomers?
They found a lot of young cool stars besides the young hot stars. Including (or excluding?) an eclipsing binary of two young brown dwarfs.Ken G said:Possibly "hot stars," possibly "interstellar medium." If you are interested in the stars that illuminate the nebula, or the history of the supernovae that made it, you might hear about these at a "hot star" meeting. I doubt cool star astronomers care much about the Orion nebula!
snorkack said:They found a lot of young cool stars besides the young hot stars. Including (or excluding?) an eclipsing binary of two young brown dwarfs.
Mind blown.stefan r said:If you are interested in cold spots on hot stars do to go to the cool conference or the hot conference?
Erribert said:According to emmited heat, the consensus seems to be that our sun may be average or slightly below. It is about at the median. This is also complicated by the definition of a star.
Erribert said:I assume you are referring to the hottest part of the sun, which lies above the surface of the sun. As we get to the surface, temperatures drop significantly. Observations suggest that below the surface temperatures drop even more. Indeed, looking into holes indicates lower temperatures...
...There appears to be no consistent temperature throughout the sun and it is very difficult to get emissions deep in the sun. So, the answer is difficult. For most other stars I think we only measure emission temperatures...
No.stefan r said:76.45% of main sequence stars are classified as M-type. So median temperature is much lower than the sun. If you list the brightest visible stars then the sun is closer to median.
snorkack said:No.
On the other side of the median.
93 brightest stars:
https://en.wikipedia.org/wiki/List_of_brightest_stars
include:
6 M stars (all giants or supergiants)
22 K stars (ditto)
2 G stars (both dwarfs)
Grand total of 30 stars as cool or cooler than Sun, including Sun itself, and 63 hotter.
Obviously Sun is a cool star.
As just pointed out, by another criterion Sun is a hot star.
... which would give very different results!stefan r said:There are 9,500 objects visible to (some) human eyes, magnitude 6.5. You could also use stars within 10 parsecs. This list
Make what?hyunxu said:This star regulus is hotter than sun.We conclude that blue stars are hotter than red and Orange.Why only "blue" stars make it
Why only blue stars are hotter than red and Orange? What's the actual relationship between this "blue colour " and "hotness"russ_watters said:Make what?
https://en.wikipedia.org/wiki/Wien's_displacement_lawhyunxu said:Why only blue stars are hotter than red and Orange? What's the actual relationship between this "blue colour " and "hotness"
'Hotter' means more energetic photons are being emitted.hyunxu said:This star regulus is hotter than sun.We conclude that blue stars are hotter than red and Orange.Why only "blue" stars make itView attachment 226999
rootone said:'Hotter' means more energetic photons are being emitted.
Usually this is a simple consequence of how massive the star is.
However other factors such as the composition of the star's elements play a part in stars luminosity profile.
So Does hotter star mean a massive star?rootone said:'Hotter' means more energetic photons are being emitted.
Usually this is a simple consequence of how massive the star is.
However other factors such as the composition of the star's elements play a part in stars luminosity profile.
rootone said:One consequence of this is that more massive stars have short lives compared to smaller ones.
Average over what?hyunxu said:So Is Sun's mass average?