Observations of the Quiet Sun During the Deepest Solar Minimum of the Past Century with Chandrayaan-2 XSM -- Elemental Abundances in the Quiescent Corona

Abstract

Elements with low First Ionization Potential (FIP) are known to be three to four times more abundant in active region loops of the solar corona than in the photosphere. There have been observations suggesting that this observed "FIP bias" may be different in other parts of the solar corona and such observations are thus important in understanding the underlying mechanism. The Solar X-ray Monitor (XSM) on board the Chandrayaan-2 mission carried out spectroscopic observations of the Sun in soft X-rays during the 2019-20 solar minimum, considered to be the quietest solar minimum of the past century. These observations provided a unique opportunity to study soft X-ray spectra of the quiescent solar corona in the absence of any active regions. By modelling high resolution broadband X-ray spectra from XSM, we estimate the temperature and emission measure during periods of possibly the lowest solar X-ray intensity. We find that the derived parameters remain nearly constant over time with a temperature around 2 MK, suggesting the emission is dominated by X-ray Bright Points (XBPs). We also obtain the abundances of Mg, Al, and Si relative to H, and find that the FIP bias is ~2, lower than the values observed in active regions.

Accepted for publication in ApJL; 10 pages, 5 figures; All figures of figure set 5 available in the tar file

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• Coronal Elemental Abundances during A-class Solar Flares Observed by Chandrayaan-2 XSM
• The First Flight of the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS)
• Coronal Densities, Temperatures and Abundances During the 2019 Total Solar Eclipse: The Role of Multi-Wavelength Observations in Coronal Plasma Characterization
• Role of small-scale impulsive events in heating the X-ray bright points of the quiet Sun
• Multi-wavelength observations by XSM, Hinode and SDO of an active region. Chemical abundances and temperatures
• New Solar Flare Calcium Abundances with no Surprises: Results from the SMM Bent Crystal Spectrometer
• Nanoflare Heating of the Solar Corona Observed in X-rays
• Evolution of Elemental Abundances During B-Class Solar Flares: Soft X-ray Spectral Measurements with Chandrayaan-2 XSM
• Limits on the axion-photon coupling from Chandrayaan-2 observations