Solar activity and responses observed in Balmer lines

S. Marchenko,G. Kopp,M. T. DeLand,S. Criscuoli,D. P. Choudhary

doi:10.1051/0004-6361/202037767

Abstract

Context. Many stars show Sun-like magnetic activity cycles, which are frequently observed by tracking changes in the chromospherically sensitive CaII H&K doublet. However, relationships between the line profile changes related to the magnetic activity seen in strong spectral transitions in other portions of a stellar spectrum are yet to be understood. Aims. We follow variability patterns in various solar lines in order to relate them to the emergence, passage, and decay of active solar regions. Methods. The line activity indices (core-to-wing ratio) for the upper Balmer lines – Hβ, Hγ, and Hδ – are constructed from the near-daily solar measurements acquired by the Ozone Monitoring Instrument and the TROPOspheric Monitoring Instrument. Results. On solar rotation timescales, the upper Balmer line activity indices closely follow variations in the total solar irradiance, r ∼ −(0.6 − 0.7), and thus frequently deviate from the behavior of the line activity indices that track chromospheric activity levels (e.g., the CH 430 nm band used in this study), specifically during passages of big sunspot groups.

Highlights

The search for exoplanets around Sun-like stars frequently calls for a detailed accounting of the intrinsic stellar activity, which is routinely assessed through changes in prominent spectral lines, CaII, NaI, and Hα in particular
Marchenko et al.: Solar activity and responses observed in Balmer lines rms of the corresponding Balmer indices: 78 ppm for the Ozone Monitoring Instrument (OMI) indices shown in Fig. 1, gradually growing to 304 ppm in the epoch of simultaneous OMI and TROPOspheric Monitoring Instrument (TROPOMI) observations
We concentrate on the high-quality early-mission OMI data taken at the egress from the peak of solar cycle 23

Summary

Introduction

The search for exoplanets around Sun-like stars frequently calls for a detailed accounting of the intrinsic stellar activity, which is routinely assessed through changes in prominent spectral lines, CaII, NaI, and Hα in particular. Using the data from Livingston et al (2007), Meunier & Delfosse (2009) found that the correlation between CaII and Hα varies throughout the solar cycle, strengthening around solar maximum and weakening at solar minimum, and displays asymmetric behavior at the ascending and descending solar-cycle branches. This complex relationship was ascribed to the different sensitivity of lines to the fluxes arising from plages and dark filaments

Results

Discussion

Conclusion