SETI bioastro: Re: [ASTRO] The Ages of Stars

From: Larry Klaes (lklaes@bbn.com)
Date: Thu Apr 20 2000 - 14:08:24 PDT


From: Ka Chun Yu <kachun@CASA.COLORADO.EDU>
Subject: Re: [ASTRO] The Ages of Stars
To: astro@lists.mindspring.com (astrolist)
Date: Thu, 20 Apr 2000 13:27:33 -0600 (MDT)
X-Mailer: ELM [version 2.5 PL2]
Sender: owner-astro@lists.mindspring.com
Reply-To: Ka Chun Yu <kachun@CASA.COLORADO.EDU>

Ron Ebert wrote:
> At 01:31 PM 04/20/2000 -0400, Amalendra Anandara wrote:
> >On Wed, 19 Apr 2000 14:32:21 -0700 Ron Ebert <ebert@citrus.ucr.edu>
> >writes:
> >>
> >>The relative abundance of elements can be
> >> found by examining the star's spectrum. Larger abundances will give you
> >> brighter spectral lines than smaller abundances.
> >
> >Thank you very much for answering my question. However, I'm a little
> >dubious about the snip above. Can we really distinguich brightnesses
> >well enough to make reasonable estimates of relative abundances? And
> >wouldn't the degree of mixing have some effect?
>
> Remember that each element has a distinctive set of spectral lines. There
> will be little or no overlap. The brightness of each set of heavier element
> lines can be compared to the brightness of hydrogen lines to get the
> relative abundances.

Actually most of the spectral lines used for identification are seen
in absorption in the stellar atmospheres. They get necessarily
deeper (or darker) with larger abundances, not brighter. Very few
stars actually have bright emission lines. Although you can compare
a key set of lines for any particular spectral type of star to known
calibrated line strengths for an abundance, in the end, the way these
are calibrated are via detailed stellar atmosphere models that take
into account abundances, temperatures, and gravities at the stellar
surface. For instance, Hydrogen emission and absorption lines from
the Sun are actually quite weak, whereas most of the absorption lines
are dominated by metals like Iron and Calcium. Without detailed
codes to model the behavior of the emitting gases, a simple
interpretation would be that the Sun consists mostly of Iron and
Calcium.

--kachun +** Center for Astrophysics and Space Astronomy, CB 389 **+
          +** University of Colorado, Boulder, CO 80309 **+
          +** Email: kachun@casa.colorado.edu **+
          +** http://casa.colorado.edu/~kachun **+



This archive was generated by hypermail 2b30 : Wed Mar 28 2001 - 16:07:53 PST