On the Relation Between Coronal Green Line Brightness and Magnetic Fields Intensity

The scattered stray light of coronagraph is a type of stray light that is generated by the objective lens as its surface defects irradiated by sunlight. The defects mainly include dust, blemishes on the lens surface, microroughness of the lens surface, and impurity and inhomogeneity of the glass. Unlike the other types of relatively-stable defects that occur after the objective lens is manufactured, the scattered stray light caused by dusts on the lens surface is difficult to quantify accurately due to the disorder and randomness of the dust accumulation. The contribution of this type of stray light to the overall stray light level is difficult to determine through any simulations or examinations. This can result in a continuous deterioration of the stray light level of a coronagraph and thus affect the observing capabilities of the instrument. To solve this issue, through analyzing the mechanism of scattered stray light and ghost image generated by the inner-occulting coronagraph, we propose a novel method to monitor the scattered stray light of dusts by utilizing different stray light correlation coefficients. In this method, we first simulate and measure the level of stray light from the ghost image of the objective lens, and then determine the flux ratio of scattered light and ghost image on the conjugate plane. Although the flux ratio varies with the accumulation of dusts on the lens surface, it keeps constant on the image plane. Therefore, the level of dust scattering light on the image plane can be obtained by using this ratio together with the level of ghost image stray light. We also validate the accuracy of this method in laboratory by applying objective lens with numerous surface cleanliness levels.

Section: Introductionmentioning

confidence: 99%

A New Method for Monitoring Scattered Stray Light of an Inner-occulted Coronagraph

Liu,

Zhang,

Sun

et al. 2024

“…The solar upper atmosphere, the corona and transition region (TR), plays a critical role in channeling mass and energy from our Sun to the interplanetary space. The million-kelvin solar corona can be observed on the ground during total solar eclipses (e.g., Qu et al 2013;Chen et al 2018) or with coronagraphs (e.g., Yang et al 2020bYang et al , 2020aZhang et al 2022b). However, these observations can only reveal coronal structures and dynamics above the limb of the solar disk.…”

Section: Introductionmentioning

confidence: 99%

The Solar Upper Transition Region Imager (SUTRI) Onboard the SATech-01 Satellite

Bai

Tian

Yuan-yong

et al. 2023

The Solar Upper Transition Region Imager (SUTRI) onboard the Space Advanced Technology demonstration satellite (SATech-01), which was launched to a sun-synchronous orbit at a height of $\sim$500 km in July 2022, aims to test the on-orbit performance of our newly developed Sc/Si multi-layer reflecting mirror and the 2k$\times$2k EUV CMOS imaging camera and to take full-disk solar images at the Ne VII 46.5 nm spectral line with a filter width of $\sim$3 nm. SUTRI employs a Ritchey-Chrétien optical system with an aperture of 18 cm. The on-orbit observations show that SUTRI images have a field of view of $\sim$ 41.6’$\times$41.6’ and a moderate spatial resolution of $\sim$8” without an image stabilization system. The normal cadence of SUTRI images is 30 s and the solar observation time is about 16 hours each day because the earth eclipse time accounts for about 1/3 of SATech-01’s orbit period. Approximately 15 GB data is acquired each day and made available online after processing. SUTRI images are valuable as the Ne VII 46.5 nm line is formed at a temperature regime of $\sim$0.5 MK in the solar atmosphere, which has rarely been sampled by existing solar imagers. SUTRI observations will establish connections between structures in the lower solar atmosphere and corona, and advance our understanding of various types of solar activity such as flares, filament eruptions, coronal jets and coronal mass ejections.

“…Another approach to determine the coronal magnetic field structures is by using magnetic field extrapolation from photospheric magnetograms taken from observations in an active region (e.g., Sun et al 2012;Aschwanden 2013;Wang et al 2015a;Chifu et al 2017;Zhu & Wiegelmann 2018;Wiegelmann & Sakurai 2021;Zhu et al 2022) or the whole corona (e.g., Schatten et al 1969;Aly 1984;Tadesse et al 2014). In addition, the combination of extreme ultraviolet (EUV) or infrared observations and magnetic-field models (e.g., Liu & Lin 2008;Liu 2009;Li et al 2017;Chen et al 2018;Zhang et al 2022) or magnetohydrodynamic (MHD) models (e.g., Dove et al 2011;Rachmeler et al 2013;Gibson et al 2016;Zhao et al 2021Zhao et al , 2019Jiang et al 2022) can also aid in the understanding of the magnetic field structures in the corona. Some previous studies determined the global stellar magnetic field structures above the surfaces through force-free extrapolation from magnetograms obtained from the Zeeman-Doppler imaging technique (e.g., Jardine et al 2002;Donati et al 2006;Johnstone et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Application of a Magnetic-field-induced Transition in Fe x to Solar and Stellar Coronal Magnetic Field Measurements

Chen¹,

Li²,

Bai³

et al. 2023

Magnetic fields play a key role in driving a broad range of dynamic phenomena in the atmospheres of the Sun and other stars. Routine and accurate measurements of the magnetic field at all atmospheric layers are of critical importance to understand these magnetic activities but in the solar and stellar coronae they are a challenge. It was recently proposed that the magnetic-field-induced transition (MIT) in Fe~{\sc{x}} can be used to measure the weak coronal magnetic fields. In this review, we present an overview of recent progresses in the application of this method in astrophysics. We start by introducing the theory underlying the MIT method and reviewing the existing atomic data critical for the spectral modeling of Fe~{\sc{x}} lines. We also discuss the laboratory measurements that verify the potential capability of the MIT technique as a probe for diagnosing the plasma magnetic fields. We then continue by investigating the suitability and accuracy of solar and stellar coronal magnetic field measurements based on the MIT method through forward modeling. Furthermore, we discuss application of the MIT method to existing spectroscopic observations taken by the Extreme-ultraviolet Imaging Spectrometer onboard \textit{Hinode}. This novel technique provides a possible solution for routine magnetic field measurements of the solar and stellar coronae but still requires further efforts to achieve accurate measurements. Finally, the challenges and prospects for future research on this topic are discussed.