arXiv subjects

Jeff Bary

Publications and source records attributed to Jeff Bary.

7 recordsLinked to original sources

arXiv2026

Rotational Modulation and Long-Term Variability of Magnetic Fields in T-Tauri Stars with IGRINS

Magnetic fields play a central role in the evolution of pre-main-sequence (PMS) stars, yet direct observational constraints on their variability over rotational and multi-year timescales remain scarce. We investigate the temporal behavior of surface magnetic fields in a sample of nine PMS stars observed with the Immersion GRating INfrared Spectrometer (IGRINS), using 489 high-resolution near-infrared spectra drawn from the Raw and Reduced IGRINS Spectral Archive. We fit each epoch with magnetic synthetic spectra to derive the mean surface magnetic field strength $\langle Bf \rangle$ and detect correlated magnetic and thermal variability in six of the nine stars while being able to recover the known stellar rotation period in at least one observing season for all six. We find that not only the mean magnetic field strength and effective temperature evolve on year-long baselines, but so does the amplitude of the rotational modulation signal (which in some cases weakens or disappears entirely). This behavior indicates that magnetic variability is driven by both changes in the total magnetic flux and the spatial distribution and contrast of surface magnetic inhomogeneities. For two stars in the sample with starspot measurements, we find that the magnetic filling factors are systematically larger than those inferred from temperature, implying that magnetic regions extend beyond the coolest spotted areas and occupy a broader fraction of the stellar surface (i.e., plages). These results provide direct evidence that PMS magnetic variability is structured, rotationally modulated, and evolves on year timescales.

astro-ph.SR↗

arXiv2025

Separating Photospheric and Starspot Magnetic Fields in Pre-Main-Sequence Stars Using IGRINS Spectroscopy

Magnetic fields in pre main sequence stars regulate angular momentum evolution, drive magnetic activity, and modify stellar structure, yet their surface distributions remain poorly constrained. Traditional single component Zeeman broadening analyses typically yield mean field strengths of 2-4 kG, sometimes exceeding the photospheric equipartition limit, and assume complete magnetic coverage. These assumptions conflict with evidence that strong fields are concentrated in cool starspots. Here we present the first systematic separation of photospheric and starspot magnetic field strengths in PMS stars, using high resolution R=45000 H and K band spectra from the Raw and Reduced IGRINS Archive. By modeling temperature and magnetic field strength simultaneously for a vetted sample of 33 Class II-III young stellar objects, we find median photospheric field strengths of 1.2 kG and median spot field strengths over two times stronger at 2.56 kG, resolving the apparent super equipartition tension and removing the need for a unity magnetic filling factor. Our results show that PMS surfaces are permeated by concentrated, kG strength spot fields covering 27-83% of the visible hemisphere. This two component framework offers a physically motivated means to reconcile spectroscopic and imaging based magnetic diagnostics and enables large scale magnetic population studies across young clusters and star forming regions.

astro-ph.SR↗

arXiv2025

Spectral Biases, Starspot Morphology, and Dynamo Transitions on the Pre-Main Sequence: Insights from the X-Shooter WTTS Library

Starspots are ubiquitous in young, low-mass stars, yet their impact on the spectral classification and fundamental parameter inference of pre-main sequence stars (PMS) has been largely overlooked. In this study, we demonstrate that cool starspots systematically distort spectral morphology and bias the effective temperatures, surface gravities, and luminosities derived for non-accreting Weak-Lined T Tauri Stars (WTTS). Using a sample of 56 WTTS with high-resolution, broad-band X-Shooter spectra, we perform two-temperature spectral fits that explicitly account for spot coverages and temperature contrasts. These composite models consistently outperform traditional single-temperature fits, particularly in the 3350-4000 K regime, where spot contributions dominate the red-optical and near-infrared flux. Moreover, we propose that surface gravity discrepancies between optical and infrared measurements are a natural consequence of spot-dominated emission in PMS stars. We find that single-temperature models can overestimate effective temperatures by up to 700 K and underestimate log g by 1-2 dex. Using spot-corrected effective temperatures, we derive masses and ages from traditional, magnetic, and spotted evolutionary models, finding that spot-corrections systematically raise inferred masses by up to 80% and stellar ages by up to 0.5 dex. These discrepancies are strongest for stars in the 0.3-0.8 solar mass range. Using starspots as a proxy for magnetic topology, we find evidence that a shift from largely axisymmetric to non-axisymmetric magnetic fields dominated by small-scale structures coincides with the formation of a radiative core during PMS evolution, effectively distinguishing between the convective and interface dynamo regimes.

astro-ph.SR↗

arXiv2024

Starspots as an Explanation for the Mysterious IYJ Continuum Excess Emission in Classical T Tauri Stars

An accurate estimation of the continuum excess emission from accretion spots and inner circumstellar disk regions is crucial for a proper derivation of fundamental stellar parameters in accreting systems. However, the presence of starspots can make disentangling the complicated multi-component emission in these systems challenging. Subtraction of a single-temperature spectral template is insufficient to account for the composite stellar emission, as we demonstrated in a recent campaign involving Weak-Lined T Tauri Stars. Here, we model the moderate resolution near-infrared spectra of Classical T Tauri Stars, presenting new spectral models that incorporate spotted stars plus emission from accretion hot-spots and a warm inner disk, allowing us to simultaneously reconstruct the entire 0.8-2.4 micrometer spectrum of our sixteen targets. Using these models, we re-derive the continuum excess emission. Our results indicate that accounting for starspots resolves the need to include a previously proposed intermediate temperature component in the IYJ excess, and highlights the importance of a proper treatment of starspots in studies of accreting low-mass stars.

astro-ph.SR↗

arXiv2016

Mapping CO Gas in the GG Tauri A Triple System with 50 AU Spatial Resolution

We aim to unveil the observational imprint of physical mechanisms that govern planetary formation in the young, multiple system GG Tau A. We present ALMA observations of $^{12}$CO and $^{13}$CO 3-2 and 0.9 mm continuum emission with 0.35" resolution. The $^{12}$CO 3-2 emission, found within the cavity of the circumternary dust ring (at radius $< 180$ AU) where no $^{13}$CO emission is detected, confirms the presence of CO gas near the circumstellar disk of GG Tau Aa. The outer disk and the recently detected hot spot lying at the outer edge of the dust ring are mapped both in $^{12}$CO and $^{13}$CO. The gas emission in the outer disk can be radially decomposed as a series of slightly overlapping Gaussian rings, suggesting the presence of unresolved gaps or dips. The dip closest to the disk center lies at a radius very close to the hot spot location at $\sim250-260$~AU. The CO excitation conditions indicate that the outer disk remains in the shadow of the ring. The hot spot probably results from local heating processes. The two latter points reinforce the hypothesis that the hot spot is created by an embedded proto-planet shepherding the outer disk.

astro-ph.GA↗

arXiv2014

Maximizing LSST's Scientific Return: Ensuring Participation from Smaller Institutions

The remarkable scientific return and legacy of LSST, in the era that it will define, will not only be realized in the breakthrough science that will be achieved with catalog data. This Big Data survey will shape the way the entire astronomical community advances -- or fails to embrace -- new ways of approaching astronomical research and data. In this white paper, we address the NRC template questions 4,5,6,8 and 9, with a focus on the unique challenges for smaller, and often under-resourced, institutions, including institutions dedicated to underserved minority populations, in the efficient and effective use of LSST data products to maximize LSST's scientific return.

astro-ph.IM↗

arXiv2014

Circumbinary Ring, Circumstellar disks and accretion in the binary system UY Aurigae

Recent exo-planetary surveys reveal that planets can orbit and survive around binary stars. This suggests that some fraction of young binary systems which possess massive circumbinary disks (CB) may be in the midst of planet formation. However, there are very few CB disks detected. We revisit one of the known CB disks, the UY Aurigae system, and probe 13CO 2-1, C18O 2-1, SO 5(6)-4(5) and 12CO 3-2 line emission and the thermal dust continuum. Our new results confirm the existence of the CB disk. In addition, the circumstellar (CS) disks are clearly resolved in dust continuum at 1.4 mm. The spectral indices between the wavelengths of 0.85 mm and 6 cm are found to be surprisingly low, being 1.6 for both CS disks. The deprojected separation of the binary is 1.26" based on our 1.4 mm continuum data. This is 0.07" (10 AU) larger than in earlier studies. Combining the fact of the variation of UY Aur B in $R$ band, we propose that the CS disk of an undetected companion UY Aur Bb obscures UY Aur Ba. A very complex kinematical pattern inside the CB disk is observed due to a mixing of Keplerian rotation of the CB disk, the infall and outflow gas. The streaming gas accreting from the CB ring toward the CS disks and possible outflows are also identified and resolved. The SO emission is found to be at the bases of the streaming shocks. Our results suggest that the UY Aur system is undergoing an active accretion phase from the CB disk to the CS disks. The UY Aur B might also be a binary system, making the UY Aur a triple system.

astro-ph.GA↗