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Star age Measurements



 
 
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  #31  
Old May 30th 13, 01:14 AM posted to sci.astro
dlzc
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Posts: 1,426
Default 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
  #32  
Old June 4th 13, 10:16 PM posted to sci.astro
Steve Willner
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Posts: 1,172
Default Star age Measurements

SW What gas has oxygen missing five electrons?

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


The first two refer to extremely hot and low-density gas that isn't
forming stars. I'm not sure of the point of the third one. Yes, the
very tenuous intergalactic gas is probably low metallicity, but I
doubt it's primordial. Wasn't the recent detection in X-rays based
on an iron line?

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


You meant "temperature is low enough" in that last (though density
comes into it, too). However, most (if not all) regions in the Milky
Way where we know stars are forming are associated with ionized gas,
and we can measure the gas metallicity. It's roughly solar,
depending on the specific cloud.

What logic was used to arrive at "0 age"?


Any cluster with high luminosity (=high mass) stars must be young.
That mostly means open clusters rather than globulars; the Orion
Nebula cluster is (without looking up the actual value) probably at
most a few Myr old. The Pleiades age estimate changed a few years
ago, but I think it's of order 100 Myr now.

I am continually told I am "wrong", without citation.


It's easy to look in ADS.

http://adsabs.harvard.edu/abs/2013A%26A...549A..60C
is a recent detailed analysis of many globular clusters in M31 and
the Milky Way. The lowest age they find is 150 Myr.

http://adsabs.harvard.edu/abs/2010PASP..122..991D
is a detailed analysis of one specific cluster.

As I say, it's not hard to find more, and there are probably course
lecture notes on the web.

SW Via stellar evolution theory (detailed computer models),

*calibrated how*?


I'm not an expert, but models have to fit the Sun, which has
exquisite helioseismology results for all but the inner 5% of its
radius. Some other stars have stellar seismology, and stars in
binary systems have known masses and distances. Models also have to
fit laboratory data on opacity and nuclear cross sections. All that
doesn't mean the models are perfect, but the models assume nothing
whatever about a Big Bang or any other cosmology.

Why do you think the reasoning is circular? Do you think astronomers
wouldn't be aware of it if it were?

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


Ah. That's a misconception all right. You can take credit for its
originality.

The Sun has an absolute visual magnitude of 4.8. If you put it at
the distance of the Virgo Cluster, which has a distance modulus of
about 31, the Sun would have an apparent magnitude of about 36.
That's far too faint to see with existing instruments, but it's not
zero flux density. Add, say, 10^11 similar stars, and the apparent
magnitude of the collection would be 8.5, easily visible in a small
telescope. In fact, M87, the brightest galaxy in the cluster, has a
visual magnitude of around 8.6, pretty close to this figure.

None of this has anything to do with dust, let alone making a star
"large enough to see." There are only rare instances in astronomy
where visible light is seen via reflection from dust. (You can look
up "reflection nebulae" for the most prominent examples.) Typically
dust along the line of sight absorbs light on its way to us and
thereby makes stars appear fainter than they would if there were no
dust. Dust absorbs blue light more than red light, so it also makes
stars appear redder. (Maybe that's what you were thinking of when
you wrote "somewhat cooler.") Taking this into account is not always
easy, but most globular clusters have essentially no internal dust.
Adding dust would make them fainter, not brighter. (All this refers
to visible light. Things are different in the infrared, where the
dust actually does emit light, but even there, reflection is not
relevant in most cases.)

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


That last isn't the reason. Adding dust would make such stars
fainter, not brighter. Such stars are invisible because they are
just too faint by themselves. However, you might look up "Magellanic
Stream" for stars that have been tidally pulled out of the LMC and
are visible in the Sloan Digital Sky Survey.

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


SW 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.


The Ring Nebula doesn't glow (in visible light) because of dust. In
general, gaseous nebulae aside, visible light measures where stars
are. You can do even better in the near infrared, out to wavelengths
of say 2 microns or so, but that's a minor technical point.

The basic point is that your misconception about needing dust to make
stars visible has given you the wrong idea.

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


There has been satellite VLBA done from low Earth orbit. In
principle the technique should work at longer baselines, but
depending on the frequency, there may be practical limitations from
interplanetary scintillation or other effects.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
  #33  
Old June 8th 13, 06:28 AM posted to sci.astro
Odysseus[_1_]
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Posts: 534
Default Star age Measurements

In article ,
(Steve Willner) wrote:

snip

In article ,
dlzc writes:


[...]

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


SW 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.


The Ring Nebula doesn't glow (in visible light) because of dust. In
general, gaseous nebulae aside, visible light measures where stars
are. You can do even better in the near infrared, out to wavelengths
of say 2 microns or so, but that's a minor technical point.


I'm not sure about the Ring, but in many planetary nebulae, and
occasionally elsewhere, the glow we see is fluorescence: X-ray and UV
emissions from very hot stars excite the surrounding gas (otherwise cool
and invisible) to re-emit down-spectrum in the visible range. Modulated
starlight, if you will, rather than simply reflected, and a little like
our own aurorae.

The basic point is that your misconception about needing dust to make
stars visible has given you the wrong idea.


Dust is harder to excite than gas.

The interior of the vast SNR-bubble whose outer margins form the Veil
Nebula shows noticeably more stars than the surrounding area, apparently
because the region has been 'blown clear'.

--
Odysseus
  #34  
Old June 10th 13, 09:32 PM posted to sci.astro
Steve Willner
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Posts: 1,172
Default Star age Measurements

In article ,
Odysseus writes:
I'm not sure about the Ring, but in many planetary nebulae, and
occasionally elsewhere, the glow we see is fluorescence:


The visible glow from gaseous nebulae, including ionized hydrogen
regions such as the Orion Nebula, is indeed from the gas, not
reflected starlight. The visible light is not continuum emission at
all wavelengths but rather is concentrated in emission lines at
discrete wavelengths. (There is some continuum emission, too, but
it's weak.) The basic physical processes were worked out in the
1930s. Fluorescence is part of the story (look up "Bowen
fluorescence mechanism"), but a bigger part is collisional excitation
of ions by electrons. The hydrogen and helium lines come from
recombination.

That's in visible light. Emission processes at other wavelengths
differ. In particular, the infrared has continuum emission from
dust. This is not reflected starlight either.

There are "reflection nebulae" and a few other cases where starlight
reflected by dust is important (including the Sun's "F corona"), but
overall such cases are pretty rare.

X-ray and UV emissions from very hot stars excite the surrounding
gas (otherwise cool and invisible) to re-emit down-spectrum in the
visible range.


Basically right, but UV is pretty much the whole story. There aren't
enough X-rays to do much excitation. Stellar temperatures in PN
central stars range from roughly 30000 K to upwards of 100000 K. In
H II regions, stellar temperatures can be somewhat lower, perhaps
down to 15000 K. The UV from the hot stars ionizes nearby gas, and
the various processes lead to emission from the gas.

Modulated starlight, if you will, rather than simply reflected,
and a little like our own aurorae.


I think the aurorae are also collisional excitation by electrons, but
the specific atoms or ions are not all the same as in ionized
nebulae.

Dust is harder to excite than gas.


Yes, in visible light. When dust absorbs visible or UV light, the
dust heats up, and warm dust radiates in the infrared. In
equilibrium, the energy in has to equal the energy out. The net
effect is converting visible or UV light to infrared, so it's the
same sort of outcome, but the physical process is different.

The interior of the vast SNR-bubble whose outer margins form the Veil
Nebula shows noticeably more stars than the surrounding area, apparently
because the region has been 'blown clear'.


In general, star counts can be used to measure extinction: more
stars, less extinction. Of course you have to be sure the true
number of background stars is constant, so the method only works over
limited areas.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
  #35  
Old June 11th 13, 05:06 PM posted to sci.astro
Brad Guth[_3_]
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Posts: 15,175
Default Star age Measurements

On May 17, 5:44*am, David Levy
wrote:
I would like to get your advice with regards to the Star age
Measurements.

This is critical element for any theory. This is a key element for
confirming the Big bang theory. Therefore, I was quite surprise to find
that this key measurement is actually based on the Big Bang theory.

Based on Wiki it is stated:

"The metallicity of an astronomical object may provide an indication of
its age. When the universe first formed, according to the Big Bang
theory, it consisted almost entirely of hydrogen which, through
primordial nucleosynthesis, created a sizeable proportion of helium and
only trace amounts of lithium and beryllium and no heavier elements.
Therefore, older stars have lower metallicities than younger stars such
as our Sun."

So the science is measuring the star age based on the fundamental Idea
of the Big bang.
With the results of the star age they are coming back and reconfirm the
Big bang theory.

This might be radicals and contradicts a basic common sense.
I assume that without the big bang theory, the Science could develop
some other method for Star age measurements.

Please advice.

--
David Levy


Mainstream science and even its physics is highly dependent upon the
Big Bang, even though there's nothing objectively supporting the BB.
In other words, we get to make do with our mainstream of circular
logic instead of objective proof of anything that truly matters.

Original BB stars of perhaps at least 1000+ solar mass(2+e33 kg) and
supposedly comprised of only hydrogen that lasted at best a few years,
is where that initial hydrogen fusion process created helium and
eventually every other known element of metallicity. So, newer stars
are those of considerably lower mass (under 10 SM), as well as having
a much higher helium content and/or hosting those heavier elements of
metals as well as their having created numerous planets that by now
should far outnumber all the stars (including brown dwarfs that are
actually large gas giants with perhaps a hundred moons each)
combined. Some of us would speculate there's at least a thousandfold
as many planets as stars, and the vast majority of them planets got
created a billion years before our solar system even formed.

The rate of hydrogen fusion consumption can be used to estimate the
given age and/or lifespan of stars, although helium fusion driven
stars are entirely another issue.



  #36  
Old June 11th 13, 08:28 PM posted to sci.astro
dlzc
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Posts: 1,426
Default Star age Measurements

Dear Brad Guth:

On Tuesday, June 11, 2013 9:06:45 AM UTC-7, Brad Guth wrote:
....
Mainstream science and even its physics is highly
dependent upon the Big Bang, even though there's
nothing objectively supporting the BB.


Say what?

In other words, we get to make do with our
mainstream of circular logic instead of objective
proof of anything that truly matters.


We can use actual data to get us back to a few hundred million years of the CMBR. And this data without "assuming" a Big Bang, points to a much smaller Universe at that time.

Beyond this CMBR curtain, Science does not do "proof", you know this, yet you continue posturing. We have theory where we have data, and cosmology (including the Big Bang) is largely "extrapolation" at best.

Does lying include what you think "truly matters"? Please do not continue to present Science arriving at any sort of proof, or failing because it *never* can do this. Only Religion, Philosophy, and Law have proofs.

David A. Smith
 




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