by MarkBour » Fri Mar 31, 2017 2:45 am
Ann wrote:
. . . By the way, I agree with starsurfer and Fred that today's APOD is a great picture!
I agree, this is a very beautiful skyscape; a composition that makes me feel calm, and at peace.
Ann wrote:
In my opinion, we should be careful how we use the term "low-mass stars". Most stars in our galaxy, and probably in the entire universe, are much less massive than the Sun. Small stars like Proxima Centauri are far more common than solar-mass stars like the Sun. The tiny stars like Proxima Centauri are the real low-mass stars. The Sun, which belongs to the top 90-95th echelon when it comes to mass of stars in the universe, should be called medium-mass stars instead.
Ann
Here, I'll play Devil's advocate. While your point is well-taken, perhaps there are stronger criteria for delineating the groups of stars (stronger than just dividing along the mean or geometric mean, etc.) Or at least, in this APOD, the emphasis is on one such criterion, and so the adjective "low-mass" in regard to that criterion would be appropriate and even instructive? Looking on Wikipedia, I see that these T Tauri stars are small enough to progress through the Hayashi contraction sequence, and that is the main characteristic they are presenting to us here.
https://en.wikipedia.org/wiki/T_Tauri_star
T Tauri stars are pre-main-sequence stars in the process of contracting to the main sequence along the Hayashi track, a luminosity-temperature relationship obeyed by infant stars of less than 3 solar masses (M☉) in the pre-main-sequence phase of stellar evolution.
![SmallDrink.JPG](./download/file.php?id=29125&sid=ca6467344a51307ca06c4077d74bb14c)
- SmallDrink.JPG (29.49 KiB) Viewed 9201 times
It further goes on to divide out Herbig Ae/Be-type stars, which are pre-main-sequence stars of (2–8 solar masses), and then more massive (>8 Solar mass) stars which are not observed in their pre-main-sequence stages.
So, that makes for a nice "small, medium, large" division.
Okay, I'm done. Excuse me, while I go have a small drink ...
[quote="Ann"]
. . . By the way, I agree with starsurfer and Fred that today's APOD is a great picture!
[/quote]
I agree, this is a very beautiful skyscape; a composition that makes me feel calm, and at peace.
[quote="Ann"]
In my opinion, we should be careful how we use the term "low-mass stars". Most stars in our galaxy, and probably in the entire universe, are much less massive than the Sun. Small stars like Proxima Centauri are far more common than solar-mass stars like the Sun. The tiny stars like Proxima Centauri are the real low-mass stars. The Sun, which belongs to the top 90-95th echelon when it comes to mass of stars in the universe, should be called medium-mass stars instead.
Ann[/quote]
Here, I'll play Devil's advocate. While your point is well-taken, perhaps there are stronger criteria for delineating the groups of stars (stronger than just dividing along the mean or geometric mean, etc.) Or at least, in this APOD, the emphasis is on one such criterion, and so the adjective "low-mass" in regard to that criterion would be appropriate and even instructive? Looking on Wikipedia, I see that these T Tauri stars are small enough to progress through the Hayashi contraction sequence, and that is the main characteristic they are presenting to us here.
[quote][url]https://en.wikipedia.org/wiki/T_Tauri_star[/url]
T Tauri stars are pre-main-sequence stars in the process of contracting to the main sequence along the Hayashi track, a luminosity-temperature relationship obeyed by infant stars of less than 3 solar masses (M☉) in the pre-main-sequence phase of stellar evolution.[/quote]
[float=right][attachment=0]SmallDrink.JPG[/attachment][/float]
It further goes on to divide out Herbig Ae/Be-type stars, which are pre-main-sequence stars of (2–8 solar masses), and then more massive (>8 Solar mass) stars which are not observed in their pre-main-sequence stages.
So, that makes for a nice "small, medium, large" division.
Okay, I'm done. Excuse me, while I go have a small drink ...