Differences of the Solar Magnetic Activity Signature in Velocity and Intensity Helioseismic Observations

TL;DR

This study compares velocity and intensity helioseismic observations over 17 years, revealing differences in p-mode frequency shifts related to solar magnetic activity and their implications for understanding solar and stellar magnetic phenomena.

Contribution

It provides a detailed analysis of the differences in p-mode frequency shifts between velocity and intensity measurements, highlighting their temporal and angular degree dependencies.

Findings

Intensity frequencies are higher than velocity frequencies during the solar cycle.

Temporal variations in frequencies show clear differences between velocity and intensity data.

Time delays are observed between GOLF and VIRGO frequency variations.

Abstract

The high-quality, full-disk helioseismic observations continuously collected by the spectrophotometer GOLF and the three photometers VIRGO/SPMs onboard the SoHO spacecraft for 17 years now (since April 11, 1996, apart from the SoHO "vacations") are absolutely unique for the study of the interior of the Sun and its variability with magnetic activity. Here, we look at the differences in the low-degree oscillation p-mode frequencies between radial velocity and intensity measurements taking into account all the known features of the p-mode profiles (e.g., the opposite peak asymmetry), and of the power spectrum (e.g., the presence of the higher degrees l= 4 and 5 in the signal). We show that the intensity frequencies are higher than the velocity frequencies during the solar cycle with a clear temporal dependence. The response between the individual angular degrees is also different. Time delays are observed between the temporal variations in GOLF and VIRGO frequencies. Such analysis is important in order to put new constraints and to better understand the mechanisms responsible for the temporal variations of the oscillation frequencies with the solar magnetic activity as well as their height dependences in the solar atmosphere. It is also important for the study of the stellar magnetic activity using asteroseismic data.