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

TL;DR

This study uses Chandrayaan-2 XSM data to analyze the quiet solar corona during the deepest solar minimum, revealing stable plasma conditions and a lower FIP bias compared to active regions, enhancing understanding of solar elemental abundances.

Contribution

First spectroscopic analysis of the quiet solar corona during a deep solar minimum using Chandrayaan-2 XSM data, providing insights into elemental abundances and plasma conditions.

Findings

Temperature around 2 MK remains stable over time.

FIP bias for Mg, Al, Si is approximately 2, lower than in active regions.

Emission dominated by X-ray Bright Points during quiet solar conditions.

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.