Limits of Spectroscopy

Ï "Andrew Urquhart" Ýãñáøå óôï ìÞíõìá
news:_0m1c.103$m56.92@newsfe1-win...
[snip]

You're going to need a good few photons to be able to remove the
uncertainty as to peaks and troughs in the wavelength profile. In this
recent story:
http://www.astronomynow.com/news/040...t_galaxy.shtml
I imagine they had enough photons to calculate an approximate blackbody
curve to determine the redshift, but I very much doubt they could tell
you what the composition of the galaxy was!

Agreed, but I took the OP question to refer to individual objects. For
(strange) galaxies, I wouldn't even bother, since as many people have
pointed out, the resultant spectra are simply integrated over thousands of
individual sources.

If one takes the spectrum of a quazar or some otherwise strange object like
a Seyfert galaxy, which often exhibit various emission wavelengths, the
spectral analysis is difficult to begin with, when it relates to "who emits
what", so I would imagine that such attempts carry much less info for
complex objects than for individual objects, unless there is some additional
evidence on the emitters and their individual spectra.

From a practical standpoint, I am even not sure what it would mean to say
"the spectrum of a strange/distant composite object is such and such".
That's like me putting together in a box 100 discharge tubes with different
elements, mix their light together and pass the resulting light through a
Lambertian diffuser and then after analyzing the light, saying "well, the
"object" appears to consist of Hg, Na, Th, In, Sc, ...". Doesn't make much
sense to me, unless I have _some_ idea about the individual components that
sit inside that box.

For example, for a regular galaxy, like M31, what kind of info can one get
if one maps the spectrum of the galaxy as a whole? I presume the dominant
radiation would come from the statistically dominant star types. That tells
one something about the larger population of stars of M31, but doesn't
otherwise say much about the less prominent members of it, which may well
exist and their radiation may be hidden from all the integrated "noise" from
the dominant star population.

I imagine the situation would be much more difficult with quazars, where the
exact mechanisms of their spectra emissions are not even known well enough
to guarantee some sort of selective filtering and analysis. What do the
emission lines from quazars actually denote? That we have individual members
who have emission lines or that there is some other mechanism which is
responsible for the emission as being the predominant radiation?
--
Andrew Urquhart
Reply: www.andrewu.co.uk/about/contact/
--
Ioannis Galidakis
http://users.forthnet.gr/ath/jgal/
------------------------------------------
Eventually, _everything_ is understandable

"beavith" wrote

[Uh, like... words and stuff]

Settle down, Beavis! What's your problem?

"Martin Brown" wrote in message
...
In message , Ioannis
writes

? "Abdul Ahad" ?????? ??? ??????
. com...

What is the faintest "source" that can be spectroscopically analysed
via a telescope for fraunhofer lines and elemental composition?

A devious answer to this is that we can analyse clouds of hydrogen gas
that happen to be in the line of sight between us and a distant quasar
no matter how faint the cloud itself may be. The light from the quasar
allows us to see the composition and redshift of the intervening gas
cloud.


Hi Martin,
Do you have a reference for this? I want to be able to give a proper
reference to people who claim that red-shift is due to 'tired light'

Cheers
Owen

In message , Tony
Flanders writes

As for other people's comments, barring the ability to measure the
energy of individual photons -- which is *not* currently possible
in the visible spectrum -- of course you need more light to do
spectroscopy than to do simple photography. How much more depends
on how finely you want to resolve those spectral lines.

Measuring the energy of individual visible light photons was once a
popular technique in the late 70's combining a large scope, spectrometer
and Boksenberg's Image Photon Counting System to do exactly that task.
It opened up the possibility of obtaining spectra from very much fainter
objects than was possible with conventional film emulsions.

Wavelength dispersion determines the energy, and the imaging system is
sensitive to single photons with good QE at suitably low intensities.
There are noise problems with it, but for a while it was the method of
choice.

Now largely supplanted by CCDs, but I think it is still used for certain
jobs.

Regards,
--
Martin Brown

In message , OG
writes

"Martin Brown" wrote in message
...
In message , Ioannis
writes

? "Abdul Ahad" ?????? ??? ??????
. com...

What is the faintest "source" that can be spectroscopically analysed
via a telescope for fraunhofer lines and elemental composition?

A devious answer to this is that we can analyse clouds of hydrogen gas
that happen to be in the line of sight between us and a distant quasar
no matter how faint the cloud itself may be. The light from the quasar
allows us to see the composition and redshift of the intervening gas
cloud.


Hi Martin,
Do you have a reference for this? I want to be able to give a proper
reference to people who claim that red-shift is due to 'tired light'

Google "Lyman forest" ought to bring something useful up.
Combine it with "tired light" and you may get exactly what you seek.

Regards,
--
Martin Brown

(Mitch Alsup) wrote in message . com...
(Abdul Ahad) wrote in message . com...
What is the faintest "source" that can be spectroscopically analysed
via a telescope for fraunhofer lines and elemental composition?

I know bright galaxies and quasars produce ample quantities of light
for spectroscopy, but surely the multiple stellar make-up of these
objects produces meaningless 'noise' at that level...

Ta.

Abdul Ahad

The distance to galaxies is determined by spectroscopic analysis.
I think the record is right at 30M; Keck verified primevil galaxies
found in one of the hubble deep fields. The big telescopes are
routinely doing spectro work at M27. This spectro work is concerned
mainly with the Lyman Alpha emissions or other ultraviolet emissions
that have been red shifted down to optical wavelengths. The detection
of the pattern is all that is necessary to determine red shift.
These are typically done on meduim resolution spectragraphs.

High resolution spectro work to determine elemental composition is
being done down to M26. Individual stars in M31 and other rather
near galaxies has been acomplished. These are done on high resolution
(see Echelle) spectrographs. Resolutions in the 0.1 Angstrom range
are routine.

High resolution work to determine shifting spectral content due to
large planets is not at this time photon limited as all the stars
are quite bright reletive to the redshift analysis stuff. The problem
for this analysis is stability of the receiving equiptment {scope
plus spectrograph} and the stability of precision reference line
sources. Resolution in the 20 Hz range allows detection of Jupiter
sized objects to several thousand light years. The stability of
the reference line source must be significantly smaller than
the spectral resolution for years at a time. Several planets have
been confirmed with amateur spectra on 20" sized telescopes.

As to noise: To the spectrograph, if photons are allowed to pass
the 'slit' the spectrograph images the spectra. So if the slit is
set at 1 arc second, the spectrograph creates a spectrum of
everything that passes the slit. Sometimes it becomes aparent
that spectral lines from several sources have been imaged at the
same time. In the early days of spectroscopy (turn of previous
century) many binary stars were determined to be binary by this
technique.

O.K. I understand the *technical* limits on spectroscopy imposed by
resolution, photon counts, etc and I suspect that spectroscopy may not
be a suitable method for analysing elemental make up of the early
universe (really far away galaxies).

Ultimately, I guess my question is: how do we deduce the fact that a
galaxy or other cosmological object beyond, say a few billion light
years distant, is lacking in heavier elements? If we cannot observe
individual 'stars' separately from their galaxies in order to deduce
their elemental composition using spectroscopy... what are the
alternatives?

My question moves more into the spehere of Astrophysics...
Specifically, if a star starts from Hydrogen/Helium fusion, going up
the scale...through Carbon burning... all the way up to Iron (for
stars of great initial mass) at the end of its evolutionary cycle,
then how do we get elements further up the scale on the Periodic Table
such as Rubidium, Strontium, Lead... all the way to Uranium? What are
the theories for their formation?

Is there a distance threshold (so many billions of years back in
time/out in space) beyond which the heaviest naturally ocurring
elements are *proved* never to have existed?

thanks.

On Thu, 4 Mar 2004 21:52:44 -0000, "Fleetie"
wrote:

"beavith" wrote

[Uh, like... words and stuff]

Settle down, Beavis! What's your problem?


he hehe HE he he kick your ass he eh hehe.

(Abdul Ahad) wrote in message . com...
Ultimately, I guess my question is: how do we deduce the fact that a
galaxy or other cosmological object beyond, say a few billion light
years distant, is lacking in heavier elements? If we cannot observe
individual 'stars' separately from their galaxies in order to deduce
their elemental composition using spectroscopy... what are the
alternatives?

Good question: we can deduce that an element is present in a star
by resolving an emission line in the star's spectrum. We can
deduce that an element is present in a gas cloud by resolving
absorption line when the gas cloud is between us and the star(s).

My question moves more into the spehere of Astrophysics...
Specifically, if a star starts from Hydrogen/Helium fusion, going up
the scale...through Carbon burning... all the way up to Iron (for
stars of great initial mass) at the end of its evolutionary cycle,
then how do we get elements further up the scale on the Periodic Table
such as Rubidium, Strontium, Lead... all the way to Uranium? What are
the theories for their formation?

The heavier elements are cooked in the milliseconds between the
colapse of the supernovaing star and the rebound of the supernovaing
star. The nuclear density goes up many times, and allows reactions
that do not occur in a normal fusion buring star. Pressure and
temperatures are extreme during this colapse through rebound phase
of the supernova, providing the environment to cook up the heavy
elements.

Is there a distance threshold (so many billions of years back in
time/out in space) beyond which the heaviest naturally ocurring
elements are *proved* never to have existed?

Another good question, and the answer you got two years ago would
not be the same answer you get today! A couple of years ago we
thought the first generation stars would have to have lifetimes of
1-2B years before supernovaing and dispersing heavy elements. We
now have evidence of the first generation stars being heavier
and thereby having shorter lives (as short as 200 M years) before
spewing heavy elements into their galaxies.

thanks.

Mtich

(Abdul Ahad) wrote in message . com...
Ultimately, I guess my question is: how do we deduce the fact that a
galaxy or other cosmological object beyond, say a few billion light
years distant, is lacking in heavier elements? If we cannot observe
individual 'stars' separately from their galaxies in order to deduce
their elemental composition using spectroscopy... what are the
alternatives?

Good question: we can deduce that an element is present in a star
by resolving an emission line in the star's spectrum. We can
deduce that an element is present in a gas cloud by resolving
absorption line when the gas cloud is between us and the star(s).

My question moves more into the spehere of Astrophysics...
Specifically, if a star starts from Hydrogen/Helium fusion, going up
the scale...through Carbon burning... all the way up to Iron (for
stars of great initial mass) at the end of its evolutionary cycle,
then how do we get elements further up the scale on the Periodic Table
such as Rubidium, Strontium, Lead... all the way to Uranium? What are
the theories for their formation?

The heavier elements are cooked in the milliseconds between the
colapse of the supernovaing star and the rebound of the supernovaing
star. The nuclear density goes up many times, and allows reactions
that do not occur in a normal fusion buring star. Pressure and
temperatures are extreme during this colapse through rebound phase
of the supernova, providing the environment to cook up the heavy
elements.

Is there a distance threshold (so many billions of years back in
time/out in space) beyond which the heaviest naturally ocurring
elements are *proved* never to have existed?

Another good question, and the answer you got two years ago would
not be the same answer you get today! A couple of years ago we
thought the first generation stars would have to have lifetimes of
1-2B years before supernovaing and dispersing heavy elements. We
now have evidence of the first generation stars being heavier
and thereby having shorter lives (as short as 200 M years) before
spewing heavy elements into their galaxies.

thanks.

Mtich

Martin Brown wrote:

[ text omitted ]

Hi Martin,
Do you have a reference for this? I want to be able to give a proper
reference to people who claim that red-shift is due to 'tired light'


Google "Lyman forest" ought to bring something useful up.
Combine it with "tired light" and you may get exactly what you seek.

Regards,


Martin:

'Tired light' is a term that suits then advocates of the BB; it is a
derogatory term that is intended to place an emotional wet blanket upon
the issue in order to discredit any possible explanation for a physical
cause of the diminution of the energy levels of photons as they traverse
the openness of space.

If you grant the recognition of physical reality to the existents in
space, rather than trying to create a metaphysical reality out of an
epistemological mathematical graphical concept of the instant locations
of gravitational acceleration forces, i.e., curved space-time, you may
find that there are causes for the "Apparent Red Shift" of light that do
not depend upon the Hubble - Doppler creationist-expansionist BB theory.

The proper scientific question to ask is, "What happens to light photons
as they traverse to openness of outer space that causes the diminution
of their energy levels?"

The issue is whether mathematical EM waves, that have no physical
existence, except insofar as the waves are the properties of actual
physical existents, i.e., photons, are valid as a metaphysical concept.
Or whether physical existents, i.e., light photons, actually have
physical properties that in interactions with other physical existents,
for example, gravitons or photons, can have different energy levels.

In terms of the validity of methods of scientific proof, the method of
'application' is an inferior method proof for the identification of
causal relationships. For example, if, due to the "Apparent Red Shift"
and the hypothesized "Doppler Effect", some Euclidean straight lines are
made to represent velocity or distance vectors, and those lines are
extended in reverse to some claimed point of intersection, or central
point or origin, the universe is claimed to not have existed prior to
that geometric extension - you know you have a problem. The fact of
existence is that existence is what it is, and that it continues to
exist as what it is. There is no reason to claim that the universe ever
did not exist or ever will exist, and that there is every reason to know
that the plurality of the universe exists continually. Period.

If you claim the Biblical creationist-expansionist -Euclidean -Hubble
-Doppler theory that leads to the suggestion of the origin of the
universe you must at the same time deny the principle of the continuity
of the plurality of universe and of all its changing existents. BB
advocates can never, for that reason find what happens to photons in
their travels that causes the "Apparent Red Shift".

BTW, the Post modernist mathematical argument that Euclid's "Parallel
Postulate" is invalid because parallel lines are impossible or that
projected lines can never meet throws cold water on the BB proposition.
To arrive at the BB hypothesis the BB advocates must admit to the
validity of Euclid's Parallel Postulate and quite a few other proved
propositions, definitions, and axioms from, at least, Book I of Euclid's
"Elements".

Existence is existing, and logic, inductive and deductive, is competent
to know the facts of the constituent existents and properties of the
plural universe, their relationships, potentials for change, and their
resulting identities.

Ralph Hertle