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Dust in the Outer Layers of Stars

Dikpati, M.

Dust in the Outer Layers of Stars [Thesis] M. Dikpati - iii, 165p.

We have studied the effects of expansion of dusty
matter in spherically symmetric atmospheres I on equivalent
widths of the spectral lines form in such media. We have
treated a two level atom in non-LTE. Initially the hydrogen
Lyman Alpha line has been studied for the purpose of calculating
the effects of number density of the neutral atoms on
equivalent widths. The temperature variation has been derived
from the assumption that the Planck function varies
as l/r2 in an atmospheres with pure hydrogen gas. Using
this temperature structure and Boltzmann equation I we calculated
the number of neutral atoms which formed the hydrogen
Lyman Alpha Line.
The dust has been introduced assuming that there
is no reemission from the dust and that dust scatters isotropic ally.
This is because the emission of dust will be
in the infrared and will not contribute to the emission
to the hydrogen Lyman
commoving frame method
line transfer equation.
Alpha Line. We have employed the
for obtaining the solution of the
The velocities of expansion are
measured in terms of mean thermal units and the amounts
of gas and dust are measured in terms of the respective
optical depths. We have considered two atmospheres: onewithout
emission and two- with emission in the medium due
to thermalization of photons.
In a static medium we obtain symmetric profiles and
when the velocity of expansion is introduced we generally
obtain P-Cygni type profiles i.e. the absorption being shifted
towards the violet side or emission peak remains at the
center gravity of the line. If we introduce dust the emission
reduce considerably whiIe dust scatters more photons
into the absorpiton core. When there is no dust the absorption
core is very wide extending approximately to three
Doppler units of either side of the center of the lines.

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