About

Adam Kowalski is an Assistant Professor at the University of Colorado Boulder, affiliated with the Department of Astrophysical and Planetary Sciences since August 2016. His research interests focus on solar and stellar astrophysics, with a specialization in spectroscopy of optical and ultraviolet emission in stellar flares. He employs state-of-the-art modeling codes combined with analysis of data from ground and space-based observatories such as Hubble, IRIS, and the APO ARC 3.5m to understand how the lower, dense stellar atmosphere, including the chromosphere and photosphere, is heated during flares in response to the sudden release of magnetic energy. Kowalski is also interested in developing new media for disseminating scientific results to the public and establishing interdisciplinary collaborations.

Research topics

• Physics
• Political Science
• Astronomy
• Computer Science
• Optics
• Astrobiology
• History
• Systems engineering
• Engineering

Selected publications

• Spatial variation of energy transport mechanisms within solar flare ribbons

  Institutional Repository (IHS Vienna) · 2026-01-06

  articleOpen access

  Solar flares release a tremendous amount of magnetic energy that subsequently manifests in several forms; the bulk of this energy is transported through the Sun’s atmosphere and explosively heats the chromosphere. While hard X-ray observations have pointed to flare-accelerated electrons as a primary means by which energy is transported following flares, alternative processes undoubtedly act alongside, or even instead of, those energetic electrons. To shed light on this we analysed flare-optimized, high-cadence Solar Orbiter observations. Footpoints from two flare ribbons were observed by the Spectral Imaging of the Coronal Environment (SPICE) instrument. Curiously, those footpoints exhibited contrasting behaviour: one had short-lived yet strong decreases in the Lyman β/Lyman γ line intensity ratio, whereas the other exhibited a more prolonged, moderate dip in that ratio. These observations were compared to synthetic spectra from radiation hydrodynamic simulations of flares driven by various energy transport mechanisms. This revealed that one footpoint was driven by energetic particle precipitation, while the other was driven by enhanced thermal heat flux. The implication is that energetic particles do not dominate along the entirety of flare ribbons. Critically, we must now focus on understanding where, when and why different mechanisms dominate in solar flare energy transport.

  PublisherDOI

• A 7 Day Multiwavelength Flare Campaign on AU Mic. IV. Quiescent Gyrosynchrotron and Gyroresonance Radiation from 12 to 25 GHz

  The Astrophysical Journal · 2026-01-21

  articleOpen access

  Abstract 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 2018 October. Using Ku -band data (12–18 GHz) from the Karl G. Jansky Very Large Array and K -band data (17–25 GHz) from the Australia Telescope Compact Array, we find that the quiescent spectrum can be decomposed into two components: one falling with frequency and one that remains flat. The flat component has a relatively steady flux density of 0.64 ± 0.14 mJy. The falling component varies in strength, but exhibits a spectral index of α = −0.88 ± 0.10. The falling component is thus consistent with nonthermal, optically thin gyrosynchrotron radiation with a corresponding power-law index similar to flares from AU Mic. While a flat component may arise from thermal, optically thin free–free emission, the observed flux density and inferred mass-loss rate are both too large compared to previous stellar wind and X-ray emission theory and models, necessitating an alternative explanation. This flat component instead matches well with an optically thick gyroresonance component integrated over multiple source regions such that the composite spectra are reasonably flat. The persistence of these components across the rotational period suggests multiple source regions, which may help explain changes in flux density and persistent high-energy electrons.

  PublisherDOI

• Spatial variation of energy transport mechanisms within solar flare ribbons

  Nature Astronomy · 2026-01-06 · 2 citations

  articleOpen access

  Solar flares release a tremendous amount of magnetic energy that subsequently manifests in several forms; the bulk of this energy is transported through the Sun's atmosphere and explosively heats the chromosphere. While hard X-ray observations have pointed to flare-accelerated electrons as a primary means by which energy is transported following flares, alternative processes undoubtedly act alongside, or even instead of, those energetic electrons. To shed light on this we analysed flare-optimized, high-cadence Solar Orbiter observations. Footpoints from two flare ribbons were observed by the Spectral Imaging of the Coronal Environment (SPICE) instrument. Curiously, those footpoints exhibited contrasting behaviour: one had short-lived yet strong decreases in the Lyman β/Lyman γ line intensity ratio, whereas the other exhibited a more prolonged, moderate dip in that ratio. These observations were compared to synthetic spectra from radiation hydrodynamic simulations of flares driven by various energy transport mechanisms. This revealed that one footpoint was driven by energetic particle precipitation, while the other was driven by enhanced thermal heat flux. The implication is that energetic particles do not dominate along the entirety of flare ribbons. Critically, we must now focus on understanding where, when and why different mechanisms dominate in solar flare energy transport.

  PublisherOA PDFDOI

• The Atmospheric Response to Large Electron Beam Fluxes in Solar Flares. III. Comprehensive Modeling of the Brightest Observed Near-ultraviolet Continuum Source in an X9 Solar Flare

  The Astrophysical Journal · 2026-01-05

  articleOpen access1st authorCorresponding

  Abstract I report on the high-resolution spectra of the remarkable X9 solar flare of 2024 October 3 (SOL2024-10-03T12:08) and evaluate the extent to which nonthermal electron beams that generate dense chromospheric condensations can power very bright kernels in solar flares. One-dimensional radiative-hydrodynamic models predict extreme H α near-wing broadening, bright continuum intensities, and a rapid Fe II red wing asymmetry evolution at the brightest near-UV (NUV) continuum source in the flare. Detailed comparisons to the spectral observations reveal that the H α line is too broad, the Fe II red wing is too bright, and the NUV continuum decays too slowly in a fiducial high-flux beam model. However, chromospheric condensations with maximum electron densities of n e ≈ 5 × 10 14 cm −3 and optical depths τ ≈ 1 in the near wing of H α are consistent with the observed intensity of a broad spectrum in the southern ribbon. Model similarities demonstrate that Fe i emission lines and the far-UV (FUV) continuum intensity can form at chromospheric heights during flares, but I find that the ratios of the NUV to FUV continuum intensities are generally too large in the models. This suggests that radiative-hydrodynamic models of chromospheric condensations cool through T ≈ 30,000 K too rapidly. The larger-than-expected FUV continuum intensities are not nearly bright enough to explain recent stellar megaflare spectra from the Hubble Space Telescope.

  PublisherDOI

• A Seven-day Multiwavelength Flare Campaign on AU Mic. III. Quiescent and Flaring Properties of the X-Ray Spectra and Chromospheric Lines

  The Astrophysical Journal · 2025-11-05 · 3 citations

  articleOpen access

  Abstract We present the X-ray quiescent and flaring properties from a unique, 7 days multiwavelength observing campaign on the M1 flare star AU Mic. Combining the XMM-Newton X-ray spectra with the chromospheric line and broadband near-UV (NUV) and optical continuum observations provides a data set that is one of the most comprehensive to date. We analyze the sample of 38 X-ray flares and study in detail the X-ray flare temperature ( T ) and emission measure (EM) evolutions of three largest flares with the X-ray flare energies of >10 33 erg. The T –EM evolution tracks and multiwavelength emission evolutions of the largest-amplitude Neupert-type flare reveal that the so-called “Flare H–R diagram” is consistent with thermal coronal flare emission evolution. The two other more gradual and longer duration X-ray flares are interpreted as having larger size scales. None of the 17 H α and H β flares show clear blue/red wing asymmetries, including the ones associated with the potential X-ray dimming event previously reported. The above largest-amplitude Neupert flare shows clear symmetric H α and H β broadenings with roughly ±400 and ±600 km s −1 , respectively, which are synchronized with the optical/NUV continuum emission evolution. Radiative hydrodynamic modeling results suggest that electron beam heating parameters that have been used to reproduce M dwarf flare NUV/optical continuum emissions can reproduce these large broadenings of H α and H β lines. These results suggest that these most energetic M dwarf flares are associated with stronger magnetic field flux densities and larger size scales than solar flares but can be interpreted in terms of the standard flare model.

  PublisherDOI

• Unveiling Unprecedented Fine Structure in Coronal Flare Loops with the DKIST

  The Astrophysical Journal Letters · 2025-08-25 · 7 citations

  articleOpen access

  Abstract We present the highest-resolution H α observations of a solar flare to date, collected during the decay phase of an X1.3-class flare on 2024 August 8 at 20:12 UT. Observations with the Visible Broadband Imager at the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST) reveal dark coronal loop strands at unprecedented spatial resolution in the flare arcade above highly structured chromospheric flare ribbons. After surveying the 20 best-seeing images, we calculate a mean loop width near the top of the arcade of 48.2 km, with a minimum loop width of ∼21 km and distribution mode of ∼43 km. The distributions of loop widths observed by the DKIST in our study are often symmetric about the mean loop width. This is initial evidence that the DKIST may be capable of resolving the fundamental scale of coronal loops, although further investigation is required to confirm this result. We demonstrate that the resolving power of the DKIST represents a significant step toward advancing modern flare models and our understanding of fine structure in the coronal magnetic field.

  PublisherDOI

• The Atmospheric Response to Large Electron Beam Fluxes in Solar Flares III: Comprehensive Modeling of the Brightest Observed Near-Ultraviolet Continuum Source in an X9 Solar Flare

  ArXiv.org · 2025-11-14

  preprintOpen access1st authorCorresponding

  I report on the high resolution spectra of the remarkable X9 solar flare of 2024 Oct 03 (SOL2024-10-03T12:08) and evaluate the extent to which nonthermal electron beams that generate dense chromospheric condensations can power very bright kernels in solar flares. 1D Radiative-hydrodynamic models predict extreme H$α$ near-wing broadening, bright continuum intensities, and a rapid Fe II red wing asymmetry evolution at the brightest NUV continuum source in the flare. Detailed comparisons to the spectral observations reveal that the H$α$ line is too broad, the Fe II red wing is too bright, and the NUV continuum decays too slowly in a fiducial high-flux beam model. However, chromospheric condensations with maximum electron densities of $n_e \approx 5 \times 10^{14}$ cm$^{-3}$ and optical depths $τ\approx 1$ in the near wing of H$α$ are consistent with the observed intensity of a broad spectrum in the Southern ribbon. Model similarities demonstrate that Fe I emission lines and the FUV continuum intensity can form at chromospheric heights during flares, but I find that the ratios of the NUV to FUV continuum intensities are generally too large in the models. This suggests that radiative-hydrodynamic models of chromospheric condensations cool through $T \approx 30,000$ K too rapidly. The larger than expected FUV continuum intensities are not nearly bright enough to explain recent stellar megaflare spectra from the Hubble Space Telescope.

  PublisherOA PDFDOI

• Unveiling Unprecedented Fine Structure in Coronal Flare Loops with the DKIST

  ArXiv.org · 2025-08-07

  preprintOpen access

  We present the highest-resolution H$α$ observations of a solar flare to date, collected during the decay phase of an X1.3-class flare on 8 August 2024 at 20:12 UT. Observations with the Visible Broadband Imager at the National Science Foundation's (NSF) Daniel K. Inouye Solar Telescope reveal dark coronal loop strands at unprecedented spatial resolution in the flare arcade above highly structured chromospheric flare ribbons. After surveying the 20 best-seeing images, we calculate a mean loop width near the top of the arcade of 48.2 km, with a minimum loop width of ~21 km and distribution mode of ~43 km. The distributions of loop widths observed by the DKIST in our study are often symmetric about the mean loop width. This is initial evidence that the DKIST may be capable of resolving the fundamental scale of coronal loops, although further investigation is required to confirm this result. We demonstrate that the resolving power of the DKIST represents a significant step towards advancing modern flare models and our understanding of fine structure in the coronal magnetic field.

  PublisherOA PDFDOI

• A 7 day Multiwavelength Flare Campaign on AU Mic. II. Electron Densities and Kinetic Energies from High-frequency Radio Flares

  The Astrophysical Journal · 2025-06-05 · 5 citations

  articleOpen accessCorresponding

  Abstract M dwarfs are the most common type of star in the solar neighborhood, and many exhibit frequent and highly energetic flares. To better understand these events across the electromagnetic spectrum, a campaign observed AU Mic (dM1e) over 7 days from the X-ray to radio regimes. Here, we present high-time-resolution light curves from the Karl G. Jansky Very Large Array (VLA) Ku band (12–18 GHz) and the Australia Telescope Compact Array (ATCA) K band (16–25 GHz), which observe gyrosynchrotron radiation and directly probe the action of accelerated electrons within flaring loops. Observations reveal 16 VLA and three ATCA flares of varying shapes and sizes, from a short (30 s) spiky burst to a long-duration (∼5 hr) decaying exponential. The Ku -band spectral index is found to often evolve during flares. Both rising and falling spectra are observed in the Ku band, indicating optically thick and thin flares, respectively. Estimations from optically thick radiation indicate higher loop-top magnetic field strengths (∼1 kG) and sustained electron densities (∼10 6 cm −3 ) than previous observations of large M dwarf flares. We estimate the total kinetic energies of gyrating electrons in optically thin flares to be between 10 32 and 10 34 erg when the local magnetic field strength is between 500 and 700 G. These energies are able to explain the combined radiated energies from multiwavelength observations. Overall, values are more aligned with modern radiative-hydrodynamic simulations of M dwarf flares, and future modeling efforts will better constrain findings.

  PublisherDOI

• Separating Flare and Secondary Atmospheric Signals with <tt>RADYN</tt> Modeling of Near-infrared JWST Transmission Spectroscopy Observations of TRAPPIST-1

  The Astrophysical Journal Letters · 2025-11-20 · 1 citations

  articleOpen access

  Abstract Although TRAPPIST-1’s temperate planets have the highest transmission signals of any known system, flares contaminate 50%–70% of transits at the 1000 ppm level, far above 100 ppm secondary atmospheric signals. Efforts to mitigate flare contamination and assess impacts on radiation environments are each hampered by a lack of empirical spectral analysis and physics-based modeling. We present spectrotemporal analysis and radiative-hydrodynamic modeling of 5.5 hr of NIRISS and NIRSpec observations of six TRAPPIST-1 flares of 2.2–8.7 × 10 30 erg. The flare lines and continua are characterized using grid searches of RADYN beam-heating models spanning 10 4 times in electron beam parameters. Best-fit models indicate these flares result from moderate-intensity beams with emergent electron fluxes of F e = 10 12 erg s −1 cm −2 and energies ≤37 keV, although all models overpredict the Paschen jump. These models predict X-ray and extreme UV (XUV), far-UV, and near-UV counterparts to the IR peak fluxes of 8.9–28.9 × 10 27 , 4.3–13.9 × 10 26 , and 3.4–11.4 × 10 27 erg s −1 , respectively. Scaling the flare rate into the XUV suggests flaring contributes 1.35 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow/> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.15</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.0</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mo>×</mml:mo> </mml:math> quiescence yr −1 . We bin integrations of similar flare effective temperature to construct fiducial flare spectra from 2000 to 4500 K, in order to develop separate empirical and RADYN -based mitigation pipelines. Both pipelines are applied to all 5.5 hr of R = 10 data, resulting in maximum residuals from 1 to 2.8 μ m of 100–140 ppm and typical residuals of 54 ± 14 and 65 ± 17 ppm for the empirical and RADYN -based pipelines, respectively. Injection testing supports a 3 σ detection capability for CO 2 atmospheres with features of 150–250 ppm, with weak evidence (Bayes factor ≈ 3) still obtained at 130 ppm. Our results motivate multiwavelength observations to improve model fidelity and test high-energy predictions.

  PublisherDOI

Recent grants

• Collaborative Research: Energy Release and Transport in Impulsive Phase of Solar Flares

  NSF · $277k · 2019–2025

Frequent coauthors

• Suzanne L. Hawley

  122 shared

• John P. Wisniewski

  121 shared

• L. Fletcher

  105 shared

• Joel C. Allred

  97 shared

• Tetsu Anan

  84 shared

• H. Lin

  University of Hawaii System

  84 shared

• Gregory D. Wirth

  82 shared

• Graham S. Kerr

  Heliophysics Science Division

  61 shared