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1. The solar wind heavy ion composition in the ascending phases of the solar cycles 23 and 25

   https://doi.org/10.3389/fspas.2024.1472874  

   Carpenter, D T; Lepri, S T; Zhao, L; Dewey, R M; Raines, J M; Livi, S; Galvin, A B; Kistler, L M (October 2024, Frontiers in Astronomy and Space Sciences)

   The approximately 11-year solar cycle has been shown to impact the heavy ion composition of the solar wind, even when accounting for streams of differing speeds; however, the heavy ion composition observed between the same specific phases of a past solar cycle and the current cycle has rarely, if ever, been compared. Here, we compare the heavy ion composition of the solar wind, as measuredin situduring the solar cycle 23 and 25 ascending phases. We examine the mean iron and oxygen charge state composition and the O⁷⁺/O⁶⁺ratio in multiple ranges of associated bulk wind speeds. Then, we compare the iron and oxygen charge state composition and relative abundance of iron to oxygen in the traditionally defined fast and slow solar wind. Finally, to determine the impact of individual ion contributions on the solar wind iron abundance, we examine individual ratios of iron and oxygen ions. Although the charge state composition remained broadly similar between these two ascending phases, both the O⁷⁺/O⁶⁺ratio and iron fractionation in fast-speed streams were higher in the solar cycle 25 ascending phase than they were during the solar cycle 23 ascending phase, suggesting that equatorial coronal hole fields more frequently reconnected with helmet streamers or active regions in the latter of the two ascending phases; however, more work will need to be done to connect these observations back to their coronal origins. The individual ion ratios used in this work provided a spectrum to analyze the aggregate elemental abundances, and this work, as a whole, is an important step in determining how conditions in the corona may vary between solar cycles between the same phases. 

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2. The S-Web Origin of Composition Enhancement in the Slow-to-moderate Speed Solar Wind

   https://doi.org/10.3847/1538-4357/acc38c  

   Lynch, B. J.; Viall, N. M.; Higginson, A. K.; Zhao, L.; Lepri, S. T.; Sun, X. (May 2023, The Astrophysical Journal)

   Abstract Connecting the solar wind observed throughout the heliosphere to its origins in the solar corona is one of the central aims of heliophysics. The variability in the magnetic field, bulk plasma, and heavy ion composition properties of the slow wind are thought to result from magnetic reconnection processes in the solar corona. We identify regions of enhanced variability and composition in the solar wind from 2003 April 15 to May 13 (Carrington Rotation 2002), observed by the Wind and Advanced Composition Explorer spacecraft, and demonstrate their relationship to the separatrix–web (hereafter, S-Web) structures describing the corona’s large-scale magnetic topology. There are four pseudostreamer (PS) wind intervals and two helmet streamer (HS) heliospheric current sheet/plasma sheet crossings (and an interplanetary coronal mass ejection), which all exhibit enhanced alpha-to-proton ratios and/or elevated ionic charge states of carbon, oxygen, and iron. We apply the magnetic helicity–partial variance of increments ( H m –PVI) procedure to identify coherent magnetic structures and quantify their properties during each interval. The mean duration of these structures are ∼1 hr in both the HS and PS wind. We find a modest enhancement above the power-law fit to the PVI waiting-time distribution in the HS-associated wind at the 1.5–2 hr timescales that is absent from the PS intervals. We discuss our results in the context of previous observations of the ∼90 minutes periodic density structures in the slow solar wind, further development of the dynamic S-Web model, and future Parker Solar Probe and Solar Orbiter joint observational campaigns. 

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3. The Sun Remains Relatively Refractory Depleted: Elemental Abundances for 17,412 Gaia RVS Solar Analogs and 50 Planet Hosts

   https://doi.org/10.3847/1538-4357/ad303e  

   Rampalli, Rayna; Ness, Melissa K; Edwards, Graham H; Newton, Elisabeth R; Bedell, Megan (April 2024, The Astrophysical Journal)

   Abstract The element abundances of stars, particularly the refractory elements (e.g., Fe, Si, and Mg), play an important role in connecting stars to their planets. Most Sun-like stars do not have refractory abundance measurements since obtaining a large sample of high-resolution spectra is difficult with oversubscribed observing resources. In this work we infer abundances for C, N, O, Na, Mn, Cr, Si, Fe, Ni, Mg, V, Ca, Ti, Al, and Y for solar analogs with Gaia Radial Velocity Spectrometer (RVS) spectra (R= 11,200) usingTheCannon, a data-driven method. We train a linear model on a reference set of 34 stars observed by Gaia RVS with precise abundances measured from previous high-resolution spectroscopic efforts (R> 30,000–110,000). We then apply this model to several thousand Gaia RVS solar analogs. This yields abundances with average upper limit precisions of 0.04–0.1 dex for 17,412 stars, 50 of which are identified planet (candidate) hosts. We subsequently test the relative refractory depletion of these stars with increasing element condensation temperature compared to the Sun. The Sun remains refractory depleted compared to other Sun-like stars regardless of our current knowledge of the planets they host. This is inconsistent with theories of various types of planets locking up or sequestering refractories. Furthermore, we find no significant abundance differences between identified close-in giant planet hosts, giant planet hosts, and terrestrial/small planet hosts with the rest of the sample within our precision limits. This work demonstrates the utility of data-driven learning for future exoplanet composition and demographics studies. 

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4. Deciphering the birth region, formation, and evolution of ambient and transient solar wind using heavy ion observations

   https://doi.org/10.3389/fspas.2022.1056347  

   Rivera, Yeimy. J.; Higginson, Aleida; Lepri, Susan T.; Viall, Nicholeen M.; Alterman, B. L.; Landi, Enrico; Spitzer, Sarah A.; Raines, Jim M.; Cranmer, Steven R.; Laming, John M.; et al (December 2022, Frontiers in Astronomy and Space Sciences)

   This paper outlines key scientific topics that are important for the development of solar system physics and how observations of heavy ion composition can address them. The key objectives include, 1) understanding the Sun’s chemical composition by identifying specific mechanisms driving elemental variation in the corona. 2) Disentangling the solar wind birthplace and drivers of release by determining the relative contributions of active regions (ARs), quiet Sun, and coronal hole plasma to the solar wind. 3) Determining the principal mechanisms driving solar wind evolution from the Sun by identifying the importance and interplay of reconnection, waves, and/or turbulence in driving the extended acceleration and heating of solar wind and transient plasma. The paper recommends complementary heavy ion measurements that can be traced from the Sun to the heliosphere to properly connect and study these regions to address these topics. The careful determination of heavy ion and elemental composition of several particle populations, matched at the Sun and in the heliosphere, will permit for a comprehensive examination of fractionation processes, wave-particle interactions, coronal heating, and solar wind release and energization that are key to understanding how the Sun forms and influences the heliosphere. 

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5. Identifying the Coronal Source Regions of Solar Wind Streams from Total Solar Eclipse Observations and in situ Measurements Extending over a Solar Cycle

   https://doi.org/10.3847/2041-8213/abe775  

   Habbal, Shadia R.; Druckmüller, Miloslav; Alzate, Nathalia; Ding, Adalbert; Johnson, Judd; Starha, Pavel; Hoderova, Jana; Boe, Benjamin; Constantinou, Sage; Arndt, Martina (April 2021, The Astrophysical Journal Letters)

   Abstract This letter capitalizes on a unique set of total solar eclipse observations acquired between 2006 and 2020 in white light, Fexi789.2 nm (T_fexi= 1.2 ± 0.1 MK), and Fexiv530.3 nm (T_fexiv= 1.8 ± 0.1 MK) emission complemented by in situ Fe charge state and proton speed measurements from Advanced Composition Explorer/SWEPAM-SWICS to identify the source regions of different solar wind streams. The eclipse observations reveal the ubiquity of open structures invariably associated with Fexiemission from Fe¹⁰⁺and hence a constant electron temperature,T_c=T_fexi, in the expanding corona. The in situ Fe charge states are found to cluster around Fe¹⁰⁺, independently of the 300–700 km s⁻¹stream speeds, referred to as the continual solar wind. Thus, Fe¹⁰⁺yields the fiducial link between the continual solar wind and itsT_fexisources at the Sun. While the spatial distribution of Fexivemission from Fe¹³⁺associated with streamers changes throughout the solar cycle, the sporadic appearance of charge states >Fe¹¹⁺in situ exhibits no cycle dependence regardless of speed. These latter streams are conjectured to be released from hot coronal plasmas at temperatures ≥T_fexivwithin the bulge of streamers and from active regions, driven by the dynamic behavior of prominences magnetically linked to them. The discovery of continual streams of slow, intermediate, and fast solar wind characterized by the sameT_fexiin the expanding corona places new constraints on the physical processes shaping the solar wind. 

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