Starship Asterisk*

Chris Peterson wrote:

Anthony Barreiro wrote:I often have to double check myself around things regarding things like higher/lower, more/less, left/right, etc. When I took algebra in high school and calculus in college (back in those days we did our calculations by scratching burnt sharpened sticks on flat rocks) I would often solve equations correctly except that somewhere along the way I had made a positive number negative, or vice versa, so I would get no credit!

A pretty crummy teacher who wouldn't see a trivial sign error in the middle of perfectly correct reasoning. An error like that should barely reduce your credit at all!

Chris Peterson wrote:

Anthony Barreiro wrote:With that disclaimer in mind, Ann's statement makes sense to me. In an old yellow star there is a high mass and a low light output. So there is a high mass to light ratio.

The way I think of it is that the mass is pretty much constant, be it an individual star over most of its life, or an entire galaxy. But the light output certainly isn't- old stars (that is, stars that have moved off the main sequence) are cooler, and not only does that shift their spectral output, but also reduces their intensity. So- constant mass, decreasing intensity means an increase in the mass-to-light ratio.

stephen63 wrote:
. http://csep10.phys.utk.edu/astr162/lect ... sslum.html

The way I read it, doubling the mass of a star results in more than an order of magnitude increase in luminosity. (11.3)
This applies to main sequence stars.
Considering the stars as one homogeneous mass won't work.

Anthony Barreiro wrote:I often have to double check myself around things regarding things like higher/lower, more/less, left/right, etc. When I took algebra in high school and calculus in college (back in those days we did our calculations by scratching burnt sharpened sticks on flat rocks) I would often solve equations correctly except that somewhere along the way I had made a positive number negative, or vice versa, so I would get no credit!

With that disclaimer in mind, Ann's statement makes sense to me. In an old yellow star there is a high mass and a low light output. So there is a high mass to light ratio.

flash wrote:

Ann wrote:If those small blue galaxies are satellites of M 109, then they aredominated by stars that are much younger than the stars that dominate M 109.

The mass-to-ligt ratio is much higher for old yellow stars than for young blue ones: in other words, you get a lot of "oomph" for the mass of young blue stars, whereas old yellow stars glow dimly for their mass.

There are billions and billions and billions of small yellow stars in the bulge, bar and lens of M 109. But the small blue companions are made up of only a fraction of that number of stars, but the stars themselves glow comparatively brilliantly.

Ann

Wouldn't that make the "mass-to-light ratio" much lower for old yellow stars than for young blue ones?

Ann wrote:If those small blue galaxies are satellites of M 109, then they aredominated by stars that are much younger than the stars that dominate M 109.

The mass-to-ligt ratio is much higher for old yellow stars than for young blue ones: in other words, you get a lot of "oomph" for the mass of young blue stars, whereas old yellow stars glow dimly for their mass.

There are billions and billions and billions of small yellow stars in the bulge, bar and lens of M 109. But the small blue companions are made up of only a fraction of that number of stars, but the stars themselves glow comparatively brilliantly.

Ann