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Abstract We present new Hubble Space Telescope (HST) UV spectra of the K2 V star HD 166620, the first star clearly recognized to be in a “magnetic grand minimum” state analogous to the Sun’s “Maunder minimum” in the late 1600s. The stellar HILyαsurface fluxes are extremely low, about a factor of 2 below fluxes observed during solar minimum, and also significantly lower than those ofτCeti (G8 V) and HD 191408 (K2.5 V), two stars more similar to HD 166620 in spectral type and age (∼10 Gyr) than the Sun. TheτCeti data that are compared with HD 166620 include both old archival data and a new HST observation as well. The Lyαdata are used to confirm a nondetection of astrospheric Lyαabsorption for this star, suggesting a very weak wind with $\dot{M}<0.1$ ${\dot{M}}_{\odot }$. The very compact astrosphere inferred forτCeti indicates that the star’s debris disk is at least partly exposed to the interstellar medium (ISM), and we discuss possible consequences. 

Abstract Coronal mass ejections (CMEs), as seen in white-light (WL) coronagraphs, often exhibit a classic three-part structure consisting of a bright front, a dark cavity, and a bright core. With the launch of Solar Orbiter, cospatial imaging of solar eruptions in multiwavelengths of extreme-ultraviolet (EUV) and WL has become available. We present a CME that erupted on 2022 September 23, observed under a uniquely favorable viewing geometry. The CME bright core and its eruptive prominence can be cospatially observed up to a coronal height of 3.5R_⊙in the middle corona, in WL using COR1 on board STEREO-A and in EUV using the Full Sun Imager on board Solar Orbiter. Cospatial, multiwavelength observations indicate that the CME bright core observed in WL was almost entirely composed of the prominence material, which was heated during the CME eruption. EUV emissions in 174 and 304 Å of the prominence were largely cospatial when the CME propagated to the middle corona, though subtle differences remained. We further discuss the potential temperature in the bright core region and find that the core was heated as it rose, likely reaching temperatures of about 0.1–0.8 MK. 

Abstract Understanding the location and evolution of the cool dense prominence in relation to the large-scale structure of coronal mass ejections (CMEs) is critical to distinguish between different CME initiation mechanisms and to further deepen our understanding of CME evolution through the heliosphere. Combining remote observations of extreme-ultraviolet images and white-light coronagraphs and heliospheric imagers (HIs) obtained from the Solar Dynamics Observatory, Solar and Heliospheric Observatory, STEREO-A, and Solar Orbiter, we present an analysis of the continuous tracking from the corona to interplanetary space of the substructures of a CME associated with a prominence that erupted on 2022 September 23. The prominence is found to remain bright and compact during the CME propagation for more than three days. We investigate the kinematic evolution of the CME substructures as the CME propagated to around 0.5 au. We find that for the first 0.28 au, both the CME front and prominence propagated coherently, indicating that the prominence was tied to the CME magnetic structure. Beyond 0.28 au, the CME bright front was seen to be distorted. However, the prominence continued to propagate at a nearly constant velocity up to at least 0.5 au. STEREO-A/HI images further show a dark ridge-like feature trailing the CME that passed over the prominence, and the prominence appeared tilted. We deduce that the prominence propagated independently of the CME at larger distances from the Sun. Overall, this study shows that both previously proposed hypotheses—namely, that the prominence is tied to or propagates independently of the CME—are valid but within different distance ranges. 

Abstract We reconstruct the morphology and kinematics of a series of small transients that erupted from the Sun on 2021 April 24 using observations primarily from Parker Solar Probe (PSP). These sequential small coronal mass ejections (CMEs) may be the product of a continuous reconnection at a current sheet, which is a macroscopic example of the more microscopic reconnection activity that has been proposed to accelerate the solar wind more generally. These particular CMEs are of interest because they are the first CMEs to hit PSP and be simultaneously imaged by it, using the Wide-field Imager for Solar Probe (WISPR) instrument. Based on imaging from WISPR and STEREO-A, we identify and model six discrete transients, and determine that it is the second of them (CME2) that first hits PSP, although PSP later more obliquely also encounters the third transient. Signatures of these encounters are seen in the PSP in situ data. Within these data, we identify six candidate magnetic flux ropes (MFRs), all but one of which are associated with the second transient. The five CME2 MFRs have orientations that are roughly consistent with PSP encountering the right-hand sides of roughly E-W oriented MFRs, which are sloping back toward the Sun. 

This perspective paper brings to light the need for comprehensive studies on the evolution of interplanetary coronal mass ejection (ICME) complexity during propagation. To date, few studies of ICME complexity exist. Here, we define ICME complexity and associated changes in complexity, describe recent works and their limitations, and outline key science questions that need to be tackled. Fundamental research on ICME complexity changes from the solar corona to 1 AU and beyond is critical to our physical understanding of the evolution and interaction of transients in the inner heliosphere. Furthermore, a comprehensive understanding of such changes is required to understand the space weather impact of ICMEs at different heliospheric locations and to improve on predictive space weather models. 

This white paper is on the HMCS Firefly mission concept study. Firefly focuses on the global structure and dynamics of the Sun's interior, the generation of solar magnetic fields, the deciphering of the solar cycle, the conditions leading to the explosive activity, and the structure and dynamics of the corona as it drives the heliosphere.