Title: 
==============
Investigation of Mode Asymmetries and Acoustic Sources

Lead Investigator:
=======
C.S. Rosenthal

E-Mail Address:
=======
rosentha@hao.ucar.edu

Team Members:
==================
T.M. Brown		     

Local Coordinator:
==================


Lead Programmer:
=====


Technical Summary:
==================
The asymmetries of p-mode lines are probably an important
diagnostic of the excitation mechanism. Recently, Mark
Rast has shown that that the asymmetry is determined by the
location of the minima or troughs in the l-nu power
spectrum whose location is determined by the depth and
characteristics of the acoustic sources. The location of
the troughs should have the same properties as the ridges
of power for a hypothetical solar model truncated at the
source depth. We intend to investigate this concept and 
attempt thereby to deduce properties of the acoustic source.



Proposal Text:
=======================
Analysis
--------

An l-nu power spectrum from 60 days of full-disk data is already
in existence and will provide an ideal starting point for the
investigation. Our primary goal is to attempt to fit the
troughs of power in this spectrum with a Duvall law, and to
compare the form of the resulting function (particularly the phase
function) with that resulting from fitting to the p-mode
ridges. It is hoped that it will be possible to deduce 
properties of the acoustic source from these results. Primarily
we would expect that the frequency dependence of the phase
function would be a diagnostic of the depth of the source.

In the second phase of the investigation
we would study the difference in line
asymmetry between intensity and doppler measurements using
the same techniques. While our primary interest is in
asymmetry as a diagnostic of physical processes in the
Sun, we are also well aware that such asymmetries can bias
the fitting of mode peaks. The unexplained difference
between mode asymmetries in doppler and intensity 
measurements is a probable cause of the systematic 
frequency differences between such measurements. Our
investigation would be intended to elucidate the physical
cause behind this difference and hence, perhaps, to
improve our ability to compensate for it.

Data Requirement
---- -----------

The first phase of the project requires access only to 
a data product which is already in existence:
the medium-l 60-day l-nu power spectrum. For
the subsequent investigations we would require doppler
and intensity l-nu spectra from comparable data runs
of sufficient length to show the line asymmetry clearly.


See Also:
=========
Rast, M.P., Unpublished results presented at the Cambridge Local
            Helioseismology Workshop