Bibcode
Bertello, L.; Henney, C. J.; Ulrich, R. K.; Varadi, F.; Kosovichev, A. G.; Roca Cortes, T.; Garcia, R. A.; Scherrer, P. H.
Bibliographical reference
American Astronomical Society Meeting 194, #108.05
Advertised on:
9
1999
Citations
1
Refereed citations
1
Description
During the years 1996 through 1998 the MDI and GOLF experiments on the
SOHO mission have provided unique and nearly uninterrupted sequences of
helioseismic observations. This paper describes the analysis carried out
on power spectra from 759 days of calibrated velocity signals provided
by these two experiments. The time series investigated in this work are
from 25 May, 1996 to 22 June, 1998. We report the results of frequency
and splitting determination of low-degree (l < 4) acoustic modes in
the frequency range between 1.5 mHz and 4.0 mHz. The power spectrum
estimation of the signals is performed using classical Fourier analysis
and the line-profile parameters of the modes are determined by means of
a maximum likelihood method. All parameters have been estimated using
both symmetrical and asymmetrical line profile-fitting formula. The line
asymmetry parameter of all modes with frequency higher than 2.0 mHz is
systematically negative and independent from l. This result is
consistent with the fact that both MDI and GOLF data sets investigated
in this paper are predominantly velocity signals. A comparison of the
results between symmetric fit and asymmetric one shows that there is a
systematic shift in the eigenfrequencies for modes above 2.0 mHz. The
results show that eigenfrequency and rotational splitting values
obtained from both the MDI and GOLF signals are in excellent agreement,
and no significant differences exist between the two data sets within
the indetermination of the measurement.