An improved multiridge fitting method for ringdiagram helioseismic analysis
Abstract
Context. There is a wide discrepancy in current estimates of the strength of convection flows in the solar interior obtained using different helioseismic methods applied to observations from the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory. The cause for these disparities is not known.
Aims: As one step in the effort to resolve this discrepancy, we aim to characterize the multiridge fitting code for ringdiagram helioseismic analysis that is used to obtain flow estimates from local power spectra of solar oscillations.
Methods: We updated the multiridge fitting code developed by Greer et al. (2014, Sol. Phys., 289, 2823) to solve several problems we identified through our inspection of the code. In particular, we changed the (1) merit function to account for the smoothing of the power spectra, (2) model for the power spectrum, and (3) noise estimates. We used Monte Carlo simulations to generate synthetic data and to characterize the noise and bias of the updated code by fitting these synthetic data.
Results: The bias in the output fit parameters, apart from the parameter describing the amplitude of the pmode resonances in the power spectrum, is below what can be measured from the MonteCarlo simulations. The amplitude parameters are underestimated; this is a consequence of choosing to fit the logarithm of the averaged power. We defer fixing this problem as it is well understood and not significant for measuring flows in the solar interior. The scatter in the fit parameters from the MonteCarlo simulations is wellmodeled by the formal error estimates from the code.
Conclusions: We document and demonstrate a reliable multiridge fitting method for ringdiagram analysis. The differences between the updated fitting results and the original results are less than one order of magnitude and therefore we suspect that the changes will not eliminate the aforementioned ordersofmagnitude discrepancy in the amplitude of convective flows in the solar interior.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 January 2020
 DOI:
 10.1051/00046361/201936662
 arXiv:
 arXiv:1911.07772
 Bibcode:
 2020A&A...633A.109N
 Keywords:

 Sun: helioseismology;
 methods: data analysis;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 Accepted for publication in A&