Star age Measurements

Dear Steve Willner:

On Wednesday, May 29, 2013 2:00:02 PM UTC-7, Steve Willner wrote:
SW One would have to ask, though, if low-metal stars are
SW forming now, why don't we see any low-metal gas?

In article ,

dlzc writes:

With space filled (in some sense) with ionized
hydrogen and oxygen missing 5 electrons, how
would we know if some of the hydrogen was new?

What gas has oxygen missing five electrons?

http://arstechnica.com/science/2012/...urrounding-us/
http://www.princeton.edu/pr/pwb/00/0...ostfound.shtml
http://astronomy.nmsu.edu/cwc/Group/QALsims/

More to the point, I thought you were suggesting
stars forming out of "new hydrogen" that lacks
metals. If that's happening, where is this
low-metallicity gas, and why don't we see it?

Ionized gas is hard to see in visible range, unless pressure is high enough to allow recombination.


SW As has been written in this thread, globular
SW clusters are assumed to be old because of
SW their HR diagrams.

Which was in turn, scaled in light of a Big Bang.

Why do you continue to assert that?

What logic was used to arrive at "0 age"? I am continually told I am "wrong", without citation.

As has been explained _multiple_ times in this
thread, the cluster ages are based entirely on
atomic physics. In other words, we observe a
cluster with a maximum main sequence luminosity
of, say, half a solar luminosity. Via stellar
evolution theory (detailed computer models),

*calibrated how*?

stars of that luminosity have about 0.8 solar
masses and take about 9 Gyr to evolve off the
main sequence. (I'm making up all the numbers,
but they are probably in the ballpark.) Thus
the cluster is 9 Gyr old. This has nothing
whatever to do with the Big Bang.

Yes, you keep saying that...

The models might, of course, be wrong (though
they are well tested on the Sun, for example,
and other stars for which one can measure
independent masses or structures), but there
is nothing circular about the reasoning.

And you keep saying that too.

Or the bullet cluster, where "all" the dust
is removed, and we can see none of the stars.

You have some strange misconception, but I'm
baffled by what it could be. Are you equating
"dust" with "dark matter?"

Dust is lit by visible light, and consequently makes the associated stars look somewhat cooler. But also large enough to see at that distance.

Dust is dark in visible light, but it isn't
what is meant by "dark matter." In particular,
most dust glows quite nicely in the infrared,
and in any case there are direct methods of
detecting dust. In all cases I can think of, it
is a tiny fraction of the mass.

Yes, just drying to get to the "visibility". We know there are extra-galactic stars by the "scads", but we cannot see them, since they have no dust...

Interpretation of the Bullet Cluster has
nothing to do with dust.

I disagree, but let's move on. Again, I am simply filling in where the OP is lacking in clarity... and I guess I am doing poorly.

When yo look at a nebula, say the ring nebula,
what is its most prominent feature, the white
dwarf, or the nebula?

What does this have to do with the light from
galaxies?

Visibility. You keep asking me where this gas is, and I keep pointing out we "only" know where the dust is that is "backlit", like a shadow play. So we don't even know where the *stars* are.

A gaseous nebula is an extended source of light.
Sizes run from perhaps a tenth of a parsec to
tens of parsecs. A collection of stars, if you
have high enough resolution, can be separated into
individual objects. Separations are typically a
parsec near the Sun and somewhat smaller in
globular clusters or galactic cores. (If you
have resolution 7 or 8 orders of magnitude better
than a parsec, you could resolve the stellar
surfaces themselves, but that's quite a leap from
resolving the cluster or galaxy.)

Sidelight... if we had three satellites in trojan with Earth, could we do VBLA techniques to achieve such resolution?

Seriously Steve, if you need to end this, just don't ask me questions. The OP has lamed out, so no need in continuing unless you need to hammer the lid on some "crap" I have spouted...

And thank you.

David A. Smith