Les Trente Glorieuses: 29 years of helioseismic observations with the Luminosity Oscillations Imager

TL;DR

This paper presents a comprehensive 29-year analysis of helioseismic data from the VIRGO instrument, revealing how solar activity influences mode characteristics and detecting low-frequency modes with unprecedented sensitivity.

Contribution

It provides the first long-term, detailed analysis of solar oscillation mode variations and reports the detection of low-frequency modes below 1600 μHz using intensity observations.

Findings

Solar activity affects mode frequencies, linewidths, and heights.

Detection of low-frequency modes below 1600 μHz.

Discrepancies in mode visibility ratios near the solar limb.

Abstract

The Luminosity Oscillations Imager (LOI) of the Variability of Solar Irradiance and Gravity Oscillations (VIRGO) instrument aboard the SoHO mission has been operating for almost the past 30 years. I report on the effect of solar activity upon mode frequencies, linewidths, height and energy rate. I report on the variation as a function of frequency for frequency, $a_2$ coefficient and linewidth changes, as well as the average over the degree and the frequency of these changes. Using the 29-year time series, I report on the frequencies, linewidths and mode height fitted with \texttt{progFIT}. Using the collapsogram technique, I also report on the detection of modes below 1600 $\mu$Hz, making the lowest frequencies detected with an instrument observing the Sun in intensity. I also report on the detection of p mode in the high voltage and guiding pixel signals with a mode height about 5 to 10 times larger than what is observed in the Sun-as-a-star signal for $l=1$. The ratios of the observed mode visibilities for the different signals are provided following a calibration of the size of the guiding pixels. While the visibility ratios for the signals excluding the limb are in good agreement with theory, those covering the solar limb are in strong disagreement.