Sun-as-a-star Spectroscopic Observations of the Line-of-sight Velocity of a Solar Eruption on 2021 October 28

Abstract

The propagation direction and true velocity of a solar coronal mass ejection, which are among the most decisive factors for its geo-effectiveness, are difficult to determine through single-perspective imaging observations. Here we show that Sun-as-a-star spectroscopic observations, together with imaging observations, could allow us to solve this problem. Using observations of the Extreme Ultraviolet Variability Experiment onboard the Solar Dynamics Observatory, we found clear blueshifted secondary emission components in extreme-ultraviolet spectral lines during a solar eruption on 2021 October 28. From simultaneous imaging observations, we found that the secondary components are caused by a mass ejection from the flare site. We estimated the line-of-sight (LOS) velocity of the ejecta from both the double Gaussian fitting method and the red-blue asymmetry analysis. The results of both methods agree well with each other, giving an average LOS velocity of the plasma of ∼423 km s−1. From the 304 Å image series taken by the Extreme ultraviolet Imager onboard the Solar Terrestrial Relation Observatory-A (STEREO-A) spacecraft, we estimated the plane-of-sky velocity from the STEREO-A viewpoint to be around 587 km s−1. The full velocity of the bulk motion of the ejecta was then computed by combining the imaging and spectroscopic observations, which turns out to be around 596 km s−1 with an angle of 42.°4 to the west of the Sun–Earth line and 16.°0 south to the ecliptic plane.

Detection of Flare-induced Plasma Flows in the Corona of EV Lac with X-Ray Spectroscopy

“…This excludes the possibility of chromospheric evaporation because in such a case, the 10 MK upflows are expected to be accompanied by an increasing density of the corresponding flaring plasma. Instead, we suggest that this is most likely caused by a plasma ejection event coupled to the flare, i.e., filament/prominence eruption, as reported by Muheki et al (2020b) on EV Lac and by Xu et al (2022) from Sun-as-a-star observations. In this scenario, the expanding magnetized structure may erupt with cool and warm materials, thus naturally resulting in the simultaneous blueshifts of cool/warm lines and a decreasing plasma density.…”

“…Solar CMEs are known as the main driver of severe space weather disturbances (Gosling 1993) and have been routinely imaged by white-light coronagraphs (Webb & Howard 2012). The possibility of CME detection through Sunas-a-star observations has also been demonstrated (Mason et al 2016;Yang et al 2022;Xu et al 2022). As their counterparts, stellar CMEs have also gained more and more attention in recent years because of the potential hazard they pose to exoplanetary space weather (Airapetian et al 2020).…”

Possible detection of coronal mass ejections on late-type main-sequence stars in LAMOST medium-resolution spectra

“…From spatially resolved extremeultraviolet (EUV) spectroscopic observations, Tian et al (2012) reported obvious blue-wing enhancements in several spectral lines during a solar CME eruption. A CME-caused blue-wing enhancement has also been detected in the Sun-as-a-star EUV spectra (Xu et al 2022). Inspired by these results, Yang et al (2022) recently developed an analytical CME model and demonstrated that stellar CMEs can also be detected through EUV spectroscopy.…”

On some features of the solar proton event on 2021 October 28 – GLE73

“…Besides the aforementioned paper by Papaioannou et al (2022), there are several other publications devoted to the analysis of the SEP-GLE73 event and associated solar activity phenomena: Battaglia, Collier, & Krucker (2022); Hou et al (2022); Li et al (2022); Klein et al (2022); Li et al (2022); Mishev et al (2022); Xu et al (2022). The solar manifestations of this event were observed with a number of spacecraft, in particular, with the Geostationary Operational Environmental Satellite (GOES; https://www.ngdc.noaa.gov/stp/satellite/goes/), the Solar and Heliospheric Observatory (SOHO; Domingo et al 1995), the Solar Dynamics Observatory (SDO; Pesnell, Thompson, & Chamberlin 2012), the Solar TErrestrial RElations Observatory (STEREO-A; Kaiser et al 2008), the Parker Solar Probe (PSP; Fox et al 2016), and the Solar Orbiter (SolO; Müller et al 2020).…”