Searching for g modes

T Appourchaux,T Corbard,J W Leibacher,P Boumier

doi:10.1051/0004-6361/201833535

Abstract

Context. The recent claims of g-mode detection have restarted the search for these potentially extremely important modes. These claims can be reassessed in view of the different data sets available from the SoHO instruments and ground-based instruments. Aims. We produce a new calibration of the GOLF data with a more consistent p-mode amplitude and a more consistent time shift correction compared to the time series used in the past. Methods. The calibration of 22 yr of GOLF data is done with a simpler approach that uses only the predictive radial velocity of the SoHO spacecraft as a reference. Using p modes, we measure and correct the time shift between ground- and space-based instruments and the GOLF instrument. Results. The p-mode velocity calibration is now consistent to within a few percent with other instruments. The remaining time shifts are within ±5 s for 99.8% of the time series.

Highlights

The detection of g modes remains a major objective of helioseismology
As it is unlikely that both time series would have time jumps at the same date, the blue SPM and Global Oscillation Network Group (GONG) provide two references for a constant time base.The GONG data were used as a time reference to check and correct GOLF datation
When the time shift agrees between the two versions of the GOLF time series, the resulting mean time difference is 0.4 ± 42 ms

Summary

Introduction

The detection of g modes remains a major objective of helioseismology. The benefit of detecting these modes would be to obtain the structure and dynamics of the very inner core of the. Very recently, Schunker et al (2018) reproduced Fig. 10 of Fossat et al (2017) They showed that using different fitting procedures, the prominent peaks at 210 nHz and its acolytes would smear out or even disappear, as seen for the time series sampled at 60 s. This leads us to investigate how the GOLF data are calibrated and whether a different calibration might or might not reproduce the results of Fossat et al (2017).

Extraction of the velocity

Correction of time shifts

Comparison of the calibration with other data sets

May 2012 23 June 2012 23 November 2014 2 September 2015 26 February 2016

Findings

Conclusion