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arXiv · 2309.03373

A comparative study of two X2.2 and X9.3 solar flares observed with HARPS-N: Reconciling Sun-as-a-star spectroscopy and high-spatial resolution solar observations in the context of the solar-stellar connection

A. G. M. Pietrow·M. Cretignier·M. K. Druett·J. D. Alvarado-Gómez·S. J. Hofmeister·M. Verma·R. Kamlah·M. Baratella·E. M. Amazo-Gomez·I. Kontogiannis·E. Dineva·A. Warmuth·C. Denker·K. Poppenhaeger·O. Andriienko·X. Dumusque·M. G. Löfdahl
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Abstract

Stellar flares cannot be spatially resolved, which complicates ascertaining the physical processes behind particular spectral signatures. Due to their proximity to Earth, solar flares can serve as a stepping stone for understanding their stellar counterparts, especially when using a Sun-as-a-star instrument and in combination with spatially resolved observations. We aim to understand the disk-integrated spectral behaviors of a confined X2.2 solar flare and its eruptive X9.3 successor as measured by HARPS-N. The behavior of multiple photospheric and chromospheric spectral lines are investigated by means of activity indices and contrast profiles. A number of different photospheric lines were also investigated by means of equivalent widths, and radial velocity measures, which are then related to physical processes directly observed in high-resolution observations made with the Swedish 1-meter Solar Telescope and SDO Our findings suggest a relationship between the evolving shapes of contrast profile time and the flare locations, which assists in constraining flare locations in disk-integrated observations. In addition, an upward bias was found in flare statistics based on activity indices derived from the Ca II H & K lines. In this case, much smaller flares cause a similar increase in the activity index as that produced by larger flares. H$\alpha$-based activity indices do not show this bias and are therefore less susceptible to activity jitter. Sodium line profiles show a strongly asymmetric response during flare activity, which is best captured with a newly defined asymmetrical sodium activity index. A strong flare response was detected in Mn I line profiles, which is unexpected and calls for further exploration. Intensity increases in H$\alpha$, H$\beta$, and certain spectral windows of AIA before the flare onset suggest their potential use as short-term flare predictors.

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A. G. M. Pietrow, M. Cretignier, M. K. Druett, J. D. Alvarado-Gómez, S. J. Hofmeister, M. Verma, R. Kamlah, M. Baratella, E. M. Amazo-Gomez, I. Kontogiannis, E. Dineva, A. Warmuth, C. Denker, K. Poppenhaeger, O. Andriienko, X. Dumusque, M. G. Löfdahl. 2023-09-06. A comparative study of two X2.2 and X9.3 solar flares observed with HARPS-N: Reconciling Sun-as-a-star spectroscopy and high-spatial resolution solar observations in the context of the solar-stellar connection. https://doi.org/10.1051/0004-6361%2F202347895

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