1. To obtain relative
abundances of the chemical elements in a stellar atmosphere, i.e.,
to determine Ne1 /Ne2,
etc., where Ne1 is the number
density of element #1 and Ne2
is the number density of element #2.
2. To obtain the ionization temperature in a stellar atmosphere. For example, comparing NFeI with NFeII implies Tion via the Saha equation.
3. To obtain the excitation
temperature in a stellar atmosphere. Comparing Nr,j
with Nr,i, where Nr,j is the number
density of some type of atom
which is in the rth ionization state and the
jth excitation state, etc., implies Texc via the
Boltzmann equation.
4. To obtain the damping
constant, a, and therefore the electron pressure, Pe,
(from the location of the turnoff point from the level to the damping
portion of the curve of growth.)
5. Occasionally, to obtain
information on the stratification in stellar atmospheres, e.g.,
the lines of neutral metals in α Persei show evidence of
greater damping constants and higher excitation
temperatures than those of ionized metals, suggesting that they are formed
deeper in the
atmosphere.
6. To obtain kinetic
temperature. Even the lines of a single ion or atom reveal
information about the kinetic temperature. The transition from Case I
(weak core) to Case II (saturated core) occurs at about
Nα0 = 1. Since α0 = (gn/gn')
Ann' λ2/(8π3/2ΔνD),
and ΔνD = α/λ = (1/λ)(2kT/M)½,
it
follows that the transition occurs at N /
T ½ = 8gn' π3/2 (2k)½
/ (gn Ann' λ2M ½).
There the higher the temperature the larger must N be be before
the "knee" of the curve of growth occurs.
