(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?

That would depend, if you float in space with a big aperture telescope
and 'stare' at a distant object for several days then the telescope is
capturing quite a lot of light which can be used to learn from.

Like amatuers who use several minute (or more) exposure cameras to
produce the excellent images occasionally posted on their websites.

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...

I can imagine a rough estimate of the general proportions of materials
in the distant galaxy can be made, though not of individual stars.