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Direct Measurement of Polar Coronal Hole-like Solar Wind in its Acceleration Phase
Samuel T. Badman, Yeimy J. Rivera, Michael L. Stevens +38
The early evolution of fast polar coronal hole (PCH) solar wind remains largely unconstrained by in situ measurements. In March 2025, Parker Solar Probe (Parker) at its closest app…
A 7 Day Multiwavelength Flare Campaign on AU Mic. IV: Quiescent Gyrosynchrotron and Gyroresonance Radiation from 12 to 25 GHz
Isaiah I. Tristan, Rachel A. Osten, Yuta Notsu +2
We present an analysis of the radio quiescent data from a multiwavelength campaign of the active M-dwarf flare star AU Mic (dM1e) that occurred in October 2018. Using Ku-band data…
Solar Wind Origin
Steven R. Cranmer
The Sun continuously expels a fraction of its own mass in the form of a steadily accelerating outflow of ionized gas called the "solar wind." The solar wind is the extension of the…
High-frequency coronal Alfvénic waves observed with DKIST/Cryo-NIRSP
Richard J. Morton, Momchil Molnar, Steven R. Cranmer +1
The presence and nature of low-frequency (0.1-10~mHz) Alfvénic waves in the corona has been established over the last decade, with many of these results coming from coronagraphic o…
Using Bright-Point Shapes to Constrain Wave-Heating of the Solar Corona: Predictions for DKIST
Samuel J. Van Kooten, Steven R. Cranmer
Magnetic bright points on the solar photosphere mark the footpoints of kilogauss magnetic flux tubes extending toward the corona. Convective buffeting of these tubes is believed to…
The Sun's Alfven Surface: Recent Insights and Prospects for the Polarimeter to Unify the Corona and Heliosphere (PUNCH)
Steven R. Cranmer, Rohit Chhiber, Chris R. Gilly +7
The solar wind is the extension of the Sun's hot and ionized corona, and it exists in a state of continuous expansion into interplanetary space. The radial distance at which the wi…
Formulating Mass-Loss Rates for Sun-like Stars: A Hybrid Model Approach
Munehito Shoda, Steven R. Cranmer, Shin Toriumi
We observe an enhanced stellar wind mass-loss rate from low-mass stars exhibiting higher X-ray flux. This trend, however, does not align with the Sun, where no evident correlation…
Magnetohydrodynamic Mode Conversion in the Solar Corona: Insights from Fresnel-like Models of Waves at Sharp Interfaces
Steven R. Cranmer, Momchil E. Molnar
The solar atmosphere is known to contain many different types of wavelike oscillation. Waves and other fluctuations (e.g., turbulent eddies) are believed to be responsible for at l…
Constraining the systematics of (acoustic) wave heating estimates in the solar chromosphere
Momchil E. Molnar, Kevin P. Reardon, Steven R. Cranmer +2
Acoustic wave heating is believed to contribute significantly to the missing energy input required to maintain the solar chromosphere in its observed state. We studied the propagat…
The Mouse that Squeaked: A small flare from Proxima Cen observed in the millimeter, optical, and soft X-ray with Chandra and ALMA
Ward S. Howard, Meredith A. MacGregor, Rachel Osten +10
We present millimeter, optical, and soft X-ray observations of a stellar flare with an energy squarely in the regime of typical X1 solar flares. The flare was observed from Proxima…
Electron Heat Flux in the Solar Wind: Generalized Approaches to Fluid Transport with a Variety of Skewed Velocity Distributions
Steven R. Cranmer, Avery J. Schiff
In the solar corona and solar wind, electron heat conduction is an important process that transports energy over large distances and helps determine the spatial variation of temper…
High-frequency wave power observed in the solar chromosphere with IBIS and ALMA
Momchil E. Molnar, Kevin P. Reardon, Steven R. Cranmer +3
We present observational constraints on the solar chromospheric heating contribution from acoustic waves with frequencies between 5 and 50 mHz. We utilize observations from the Dun…
Discovery of an Extremely Short Duration Flare from Proxima Centauri Using Millimeter through FUV Observations
Meredith A. MacGregor, Alycia J. Weinberger, R. O. Parke Loyd +17
We present the discovery of an extreme flaring event from Proxima Cen by ASKAP, ALMA, HST, TESS, and the du Pont Telescope that occurred on 2019 May 1. In the millimeter and FUV, t…
A Refined Model of Convectively-Driven Flicker in Kepler Light Curves
Samuel J. Van Kooten, Evan H. Anders, Steven R. Cranmer
Light curves produced by the Kepler mission demonstrate stochastic brightness fluctuations (or "flicker") of stellar origin which contribute to the noise floor, limiting the sensit…
Inward Propagating Plasma Parcels in the Solar Corona: Models with Aerodynamic Drag, Ablation, and Snowplow Accretion
Steven R. Cranmer, Craig E. DeForest, Sarah E. Gibson
Although the solar wind flows primarily outward from the Sun to interplanetary space, there are times when small-scale plasma inflows are observed. Inward-propagating density fluct…
An Updated Formalism For Line-Driven Radiative Acceleration and Implications for Stellar Mass Loss
Aylecia S. Lattimer, Steven R. Cranmer
Radiation contributes to the acceleration of large-scale flows in various astrophysical environments because of the strong opacity in spectral lines. Quantification of the associat…
Turbulent generation of magnetic switchbacks in the Alfvénic solar wind
Munehito Shoda, Benjamin D. G. Chandran, Steven R. Cranmer
One of the most important early results from the Parker Solar Probe (PSP) is the ubiquitous presence of magnetic switchbacks, whose origin is under debate. Using a three-dimensiona…
Updated Measurements of Proton, Electron, and Oxygen Temperatures in the Fast Solar Wind
Steven R. Cranmer
The high-speed solar wind is typically the simplest and least stochastic type of large-scale plasma flow in the heliosphere. For much of the solar cycle, it is connected magnetical…
How the breakout-limited mass in B-star centrifugal magnetospheres controls their circumstellar H-alpha emission
Stanley P. Owocki, Matt E. Shultz, Asif ud-Doula +3
Strongly magnetic B-type stars with moderately rapid rotation form `centrifugal magnetospheres' (CMs), from the magnetic trapping of stellar wind material in a region above the Kep…
Solar Analogs as a Tool to Understand the Sun
Allison Youngblood, Steve Cranmer, Sam Van Kooten +6
Solar analogs, broadly defined as stars similar to the Sun in mass or spectral type, provide a useful laboratory for exploring the range of Sun-like behaviors and exploring the phy…
The relative emission from chromospheres and coronae: dependence on spectral type and age
Jeffrey L. Linsky, Brian E. Wood, Allison Youngblood +12
Extreme-ultraviolet and X-ray emissions from stellar coronae drive mass loss from exoplanet atmospheres, and ultraviolet emission from stellar chromospheres drives photo-chemistry…
The Effect of Solar Wind Expansion and Non-Equilibrium Ionization on the Broadening of Coronal Emission Lines
Chris R. Gilly, Steven R. Cranmer
When observing spectral lines in the optically-thin corona, line-of-sight (LOS) effects can strongly affect the interpretation of the data, especially in regions just above the lim…
Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST)
Mark P. Rast, Nazaret Bello González, Luis Bellot Rubio +84
The Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand and model the basic physical processes that control the structure and dynamics of…
Heating Rates for Protons and Electrons in Polar Coronal Holes: Empirical Constraints from the Ultraviolet Coronagraph Spectrometer
Steven R. Cranmer
Ultraviolet spectroscopy of the extended solar corona is a powerful tool for measuring the properties of protons, electrons, and heavy ions in the accelerating solar wind. The larg…