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: http://star.arm.ac.uk/~csj/research/ehe_review/node4.html
Дата изменения: Fri Jan 25 15:37:50 2002 Дата индексирования: Tue Oct 2 09:35:36 2012 Кодировка: Поисковые слова: earth's atmosphere |
To test whether any evolutionary model is correct, reliable tests are
required. These include a detailed comparison between models which
predict evolution tracks and surface composition for a given stellar
mass and accurate observations of stellar compositions and
dimensions. Stellar compositions, temperatures and gravities can be
measured relatively simply, but measuring mass is less
straightforward. There are three principal approaches.
Spectroscopic Mass . Suppose some physical
mechanism connects the mass
of the star to its luminosity
,
such as the mass-luminosity relation for main-sequence stars or a
core-mass shell-luminosity relation for shell-burning stars. From
spectroscopy and model atmospheres, the effective temperature
and
surface gravity
of the star can be measured. Since
, then the spectroscopic mass
of the star may be
deduced using an appropriate
relation (e.g. Jeffery 1988).
Pulsation Mass . Stellar pulsations provide
much more powerful tools for determining stellar masses. Fortuitously,
pulsations appear to be common amongst EHes (see next section). The
most straightforward approach is provided by pulsation periods
obtained from photometry. Linear theory provides theoretical pulsation
periods for stellar models of given
and
. In conjunction
with spectroscopic measurements of
and
,
can provide an
estimate of the pulsation mass
.
Direct Mass . In some cases, it may be
possible to measure the angular radius (
) and radial velocity
(
) of a pulsating stars throughout the pulsation cycle.
may be
integrated to yield the total radius change
.
gives the relative radius change. The stellar radius
is then given by
. Following Baade (1926) and combining the radius with
from spectroscopy and model atmospheres yields the direct mass
.