Helioseismological measurements of the distribution of helium inside the Sun
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**Session 123 -- Solar Magnetic Field and Solar Variabilty**
*Oral presentation, Thursday, 12, 1995, 2:00pm - 3:30pm*

## [123.01] Helioseismological measurements of the distribution of helium inside the Sun

*A. G. Kosovichev (HEPL, Stanford U)*
Helioseismology provides a unique tool for investigating chemical
composition of the interior of the Sun. There are two basic ways
of obtaining the information. The first one is to calibrate theoretical
solar models by comparing either the observed oscillation frequencies
with the eigenfrequencies of the models, or primary seismic parameters
(e.g. the sound speed, the density and the adiabatic exponent)
inverted from the observed frequencies with
the corresponding parameters of the solar models. The second approach
is to measure abundances by direct (`secondary') inversions of the
frequencies,
incorporating additional equations of the stellar structure into
the helioseismic inverse problem. The additional equation to estimate
composition of the convection zone is the equation of state
which relates variations of the adiabatic exponent in zones of
ionization of elements to their abundances. In the radiative interior
where the most abundant elements are almost totally ionized, the
energy equations together with equations of the energy generation rate
and the opacity are used to relate primary seismic parameters
with abundances.

Inversions of the current solar data give a value for the helium
abundance in the convection zone,
which is significantly lower than the value in standard solar models,
thus suggesting that gravitational settling of helium takes place in the Sun.
This is consistent with the inversion results
in the radiative interior,
where evidence is found for large-scale material redistribution.
There is also indication of variations of the helium abundance
in the energy-generating core, which are not described by standard
solar evolution theory.

It is anticipated that the new data from the GONG and SOI will
substantially improve accuracy of the measurements of the helium
abundance.

**Thursday
program listing**