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Yaguang Li

Publications and source records attributed to Yaguang Li.

At least 19 recordsLinked to original sources
arXiv2026

Designing Versatile Samples for Learned Trajectory Scoring

Many current end-to-end driving policies emit a pool of candidate trajectories and select one, which makes selection a separable component: a scorer can be retrained while the planner, its backbone, and its trajectory generator all stay frozen. However, many strong planners concentrate their proposals around safe mode, providing limited supervision near decision boundaries. In this work, we design a training dataset that provides more informative supervision for the scorer. In particular, we construct two generators that perturb the logged human trajectory along the two axes a vehicle can be displaced: laterally toward the drivable boundary and longitudinally toward a leading vehicle. The designed dataset produces more informative positive and negative samples than the base planner's proposal pool. We attach a transformer-based scorer to two frozen generative planners, DiffusionDrive and MeanFuser, and train it on the NAVSIM navtrain dataset. The results of the experiments show that we achieve 90.1 EPDMS on DiffusionDrive and 90.4 EPDMS on MeanFuser when using ResNet-34, with 0.4 and 0.3 EPDMS respectively, from the designed training dataset.

cs.RO↗
arXiv2026

The $\delta$ Scuti pulsator occurrence as a function of age, $T_{\rm eff}$, rotation, and metallicity

Many A- and F- type stars do not display $\delta$ Scuti pulsations, despite being located within the instability strip. We use photometry from the TESS Mission to discover and study $\delta$ Scuti pulsators in open clusters within 500 pc and with ages between ~20 and 900 Myr, which provide a unique opportunity to study $\delta$ Scuti pulsators in coeval populations with uniform chemical composition. We measure pulsator occurrence, which corrects the pulsator fraction for incompleteness, across all clusters. We find that clusters younger than 200 Myr tend to exhibit higher occurrence rates, with an average occurrence of 88$\pm$3\%. The occurrence rates in clusters older than 200 Myr tend to resemble the pulsator fraction of field-star samples, with an average occurrence of 62$\pm$3\%. In addition, we find that pulsators tend to rotate more rapidly in older clusters than their younger counterparts and that hotter pulsators may stop pulsating earlier than their cooler counterparts. These results show that pulsator occurrence decreases with age and that rapid rotation is critical in maintaining $\delta$ Scuti pulsations over time.

astro-ph.SR↗
arXiv2026

SCALE: Self-Supervised Constraint-Aware Layout GEneration for Local P&R DRV Fixing at Advanced Nodes

As semiconductor manufacturing advances toward sub-2nm nodes, local place-and-route (P&R) design-rule violation (DRV) fixing is increasingly limited by complex rule interactions, dense multi-layer routing geometries, and foundry-specific constraints. While Large Language Models (LLMs) have recently demonstrated strong capabilities in EDA scripting and documentation, their application to visual layout understanding remains largely unexplored: diagnosing DRC violations from layout imagery demands precise geometric reasoning and foundry-specific rule knowledge absent from general-purpose VLM training. We propose SCALE, a framework with a self-supervised layout-generation stage for local DRV fixing at advanced nodes. Multi-layer layout geometry is serialized into structured text, and a fine-tuned language model learns to reconstruct randomly masked polygons from surrounding BEOL context alone without violation labels. At inference, natural-language rule constraints and high-temperature sampling steer generation toward diverse, violation-prone layout variants validated by an industrial signoff DRC checker, producing DRC-annotated layout--violation pairs used to fine-tune a domain-adapted DRC-VLM. This VLM provides rule-aware geometric guidance for local DRV repair, boosting state-of-the-art agents' solve rates by +12--25% (up to 97%) on 100 real sub-2nm cases spanning enclosure, spacing, width, and color-spacing violations.

cs.CV↗
arXiv2026

Exploring the Small-scale Magnetic Fields in the Atmosphere of HD 49385 by Asteroseismic Analysis

Recent asteroseismic studies have shown convincing evidences that magnetic fields may exist in the interior of some pulsating red giants. Inspired by this breakthrough, we explored the effect of small-scale magnetic fields on the p-mode oscillations in an evolved star, HD 49385. {\bf We incorporate a modified Eddington $T$-$\tau$ equation that phenomenologically mimics the effect of the magnetic fields in the atmosphere of HD 49385,} and calculate the frequencies of p-modes with $l=0$, 1, and 2. By comparing the calculated frequencies with the observed ones, we select two best-fit models with either GS98 or A09 chemical composition. Our best-fit models not only fit satisfactorily the observed frequencies, but also well reproduce some spectroscopically observed stellar parameters such as effective temperature and log\,$g$. Based on the two best-fit models, we have estimated that the small-scale magnetic fields possess a strength of approximately 80\,G and spread concentratively at approximately a height of 1850 km in the atmosphere. By selecting the best-fit models with special requirement on the avoided-crossing mode, we have confirmed that the frequency of the avoided-crossing mode is tightly related to the helium core of the star, and determined the size of the helium core as 0.117${\rm M}_\odot$ in mass and 0.078${\rm R}_\odot$ in radius. Based on the improvements of previous two sides, we can accurately determine the mass of HD 49385 to be $1.25\pm 0.02\,{\rm M}_\odot$ with an age of 4.1\,Gyr for GS98 composition and 4.5\,Gyr for A09 composition.

astro-ph.SR↗
arXiv2026

Asteroseismic Analysis of a Red Giant KIC 9145955 by Including the Small-scale Magnetic Fields in the Atmosphere

Recent convincing evidence is found within asteroseismology that suggests the magnetic fields exist in three red giants. Research on small-scale magnetic fields in the Sun and HD 49385 has shown that they have a certain corrective effect on the systematic discrepancies between observed and theoretical frequencies. Here we apply a similar method applied for the Sun to a red giant, KIC 9145955, to explore the impact of small-scale magnetic fields in the photosphere on its frequencies. We find that the calculated frequencies of our best-fit model, which simulates the effect of the magnetic fields by artificially modifying the Eddington $T-\tau$ relation, perfectly match those of the observed l = 0, 1, and 2 modes, indicating the existence of small-scale magnetic fields with an upper strength limit of 65 G and concentrating at a height 13,100 km in the photosphere. Based on the best-fit model, we revise the stellar parameters of KIC 9145955 as: $M = 1.23\pm0.04\,M_\odot$, $R = 5.57\pm0.06\,R_\odot$, $L = 19.85\pm0.5\,L_\odot$, $Age = 3.83\pm0.5$\,Gyr, $M_{\rm He} = 0.2108\pm0.0005M_\odot$, and $R_{\rm He} = 0.0306\pm0.0001R_\odot$.

astro-ph.SR↗
arXiv2026

GASTAG evolutionary tracks and isochrones from coupled 1D and 3D models: Systematic temperature offsets in red giants

Models of stellar structure and evolution describe the global and internal properties of stars throughout their lifetimes and are indispensable for studies of stellar clusters and Galactic evolution. However, most 1D evolutionary calculations rely on simplified treatment of convection, resulting in inaccurate near-surface structures and non-negligible uncertainties in the predicted fundamental parameters of low-mass stars. In a series of previous works, a novel approach was developed to couple 1D stellar interior models with 3D model atmospheres throughout the evolutionary calculation. This 1D-3D coupling method makes predicted stellar properties effectively independent of the mixing-length parameter. To expand this framework to ensemble studies of stars and age determinations of clusters, we present the GASTAG stellar evolutionary tracks and isochrones constructed using the 1D-3D coupling approach. Comparing effective temperatures from the APOGEE-Kepler catalog with GASTAG predictions, we find the theoretical temperatures are cooler by about 70 K near solar metallicity. Our isochrones are compared with observed color-magnitude diagrams of star clusters spanning from $\rm [Fe/H] = 0.3$ to $-1.9$. In all cases, the synthesized and observed diagrams agree excellently in the main-sequence, turn-off, and subgiant regions, while isochrones predict systematically cooler red giant branches. Taking these independent findings together reveals that the temperature mismatch is most likely due to deficiencies in stellar models. Because GASTAG is constructed using a method that substantially reduces uncertainties associated with surface boundary conditions and the mixing-length parameter, the difference between modeling and observation can be more confidently attributed to other ingredients in the models, such as $\alpha$-element abundances or uncertainties in low-temperature opacities.

astro-ph.SR↗
arXiv2026

The Pan-Pacific Planet Search -- IX. A menagerie of companions orbiting evolved stars

We present resolutions as to the nature of six speculative candidate companions proposed in the final data release of the Pan-Pacific Planet Search, a 6-year radial-velocity survey of 164 southern evolved stars using the now-decommissioned UCLES spectrograph on the 3.9m Anglo-Australian Telescope. New radial-velocity observations, TESS asteroseismology, and Hipparcos-Gaia astrometry are incorporated to refine the companion and host-star parameters. We confirm that HD 126105b is a giant planet ($P=524.0\pm$2.9 d, $m$ sin $i=1.67^{+0.19}_{-0.17}M_{Jup}$), and that HD 205577B is a massive, eccentric brown dwarf ($P\sim$11.2 yr, $m=77^{+11}_{-9}M_{Jup}$, $e=0.68$). HD 115066B and HD 121156B are low-mass stellar companions, while HD 114899 and HD 159743 are shown to be unadorned by any detectable companions whatsoever. This demonstrates the utility of astrometric information to help overcome the temporal limitations of incomplete radial-velocity data sets and elucidate the true nature of suspected companion bodies.

astro-ph.EP↗
arXiv2026

CHARA Interferometry and TESS Asteroseismology of the Core-Helium Burning Red Giant $\kappa$ Cyg

We present a detailed study of the secondary red clump star, $\kappa$ Cyg, by combining long-baseline visible interferometry using the PAVO beam combiner at the CHARA Array with high-precision asteroseismology from TESS. This dual approach allowed for a stringent test of stellar evolutionary models in the core helium-burning phase, which remains a regime of significant theoretical uncertainty. Using the PAVO interferometric data and fitting the limb-darkened intensity profile directly, we measured $R = 8.65\pm0.10 \rm R_\odot$. We fitted the spectral energy distribution (SED) using Phoenix model atmospheres and calculated $L = 44.46 \pm 1.09 \rm L_\odot$ and $T_{\rm eff} = 5066^{+47}_{-50} \mathrm{K}$. Using 16 sectors of TESS photometry, we detected clear solar-like oscillations in $\kappa$ Cyg. Through comparison of oscillation frequencies with MESA grids using either predictive mixing (PM) or exponential overshooting (OS), we found that models reproducing the oscillation frequencies systematically overestimate the stellar radius, with overshooting models performing only marginally better. The same models also under-predict the observed dipole-mode period spacing ($\Delta\Pi_1$). By inspecting the phase offset ($\epsilon_p$), we conclude that models misrepresent the interior structure of the star. Our results demonstrate that matching envelope-dominated asteroseismic observables alone is insufficient to ensure a correct core or even global structure, and highlight the need for improved treatments of convective boundary mixing in the models of core helium-burning (CHeB) stars.

astro-ph.SR↗
arXiv2026

Asteroseismic Diagnostics for Red Giants with Kepler: Measuring epsilon and Small Frequency Separations in 16,000 Stars

Asteroseismic studies of red giants have primarily relied on two global parameters: the large frequency separation (Dnu) and the frequency of maximum power (numax). Meanwhile, the p-mode phase shift (epsilon) and small frequency separations (dnu01, dnu02), which offer additional constraints on stellar interiors, remain underexplored due to measurement challenges. Here we develop an automated pipeline based on collapsed echelle diagrams and apply it to about 16,000 Kepler red giants, jointly measuring Dnu, epsilon, dnu01, and dnu02 and assembling the largest homogeneous catalogue of these quantities to date, together with updated Dnu values and formal internal uncertainties. Using this catalogue, we quantify evolutionary trends across the red-giant branch and core-helium-burning phase. We find that dnu02/Dnu stays nearly constant for RGB stars and, for core-helium-burning stars, organises into two sequences that are systematically offset but partially overlap, broadly separating stars in the red-clump and secondary-clump regimes. We also trace the mass- and metallicity-dependent helium-flash transition. Meanwhile, epsilon follows a single Dnu-epsilon relation common to both evolutionary phases. Comparisons with stellar-evolution models reveal systematic offsets in epsilon and dnu01, which we interpret as signatures of near-surface and outer-envelope modelling deficiencies. These comparisons further suggest that dipole-mode small separations are sensitive to mode-dependent surface terms in evolved stars. Overall, our results demonstrate that epsilon and the small separations provide important diagnostics of core structure, convective-boundary mixing, and helium ignition that are complementary to those provided by Dnu and numax alone. The resulting catalogue offers a reference for testing and calibrating future stellar-evolution models.

astro-ph.SR↗
arXiv2026

Global asteroseismology of 19,000 red giants in the TESS Continuous Viewing Zones

TESS (Transiting Exoplanet Survey Satellite) has produced long-term photometry for millions of stars across the sky. In this work, we present an asteroseismic catalogue of 19,151 red giants in the TESS Continuous Viewing Zones using sectors 1--87 (Years 1--7). We visually assessed the power spectra for oscillations, and then applied the computationally efficient nuSYD method to confirm reliability. We identified an increase of 80% in the number of previously known oscillating red giants at a TESS magnitude $>$ 8. We determined the frequency of maximum power ($\rm \nu_{max}$) and the large frequency separation ($\rm \Delta \nu$) using the pySYD pipeline, achieving typical precisions of 1.5% and 1%, respectively. We classified the stars into Red Giant Branch (RGB) and Core Helium Burning (CHeB) classes using a Convolutional Neural Network. Using spectroscopic data for 10,298 stars with reliable asteroseismic measurements, we have been able to measure stellar mass and radii with precisions of 7.5% and 2.8%, which is comparable to that from 4-yr $Kepler$ data. A comparison of the seismic radii with Gaia radii shows excellent agreement. With three years of TESS data, the asteroseismic parameters are precise enough to identify the RGB bump and delineate the Zero Age Helium Burning edge. Combined with astrometric data, these parameters reveal established trends across the Galactic plane, providing a valuable set of uniformly determined asteroseismic parameters for Galactic Archaeology.

astro-ph.SR↗
arXiv2026

The KPF-SLOPE Survey - Small, Compact Multi-Planet Systems Appear Spin-Orbit Aligned

The angle between stellar spin axes and planetary orbits -- stellar obliquity -- probes the dynamics of planetary migration and evolution. The obliquities of giant planets have been extensively studied because they are the most easily measured. Smaller planets, while more difficult to measure, have the advantage of better reflecting the dynamics of planetary systems because they trigger negligible back-reactions onto the host star. This paper introduces a new observational campaign called the Small, Low-mass Oblique Planets Experiment (SLOPE) survey with the Keck Planet Finder (KPF) spectrograph, and presents four new obliquity measurements. The SLOPE survey focuses on planets smaller than Saturn across a variety of system architectures. The sky-projected obliquities of the four planets measured -- TOI-1386b, TOI-480b, TOI-4596b, and TOI-1823b -- are all consistent with spin-orbit alignment. We validate the planetary nature of TOI-4596b with a significant obliquity detection. Including these measurements, we conducted a statistical analysis of the obliquities of sub-Saturn size planets in different planetary system architectures. Compared to other architectures, those in compact multi-planet systems reside in orbits that appear preferentially aligned with the stellar equator with 6 sigma confidence.

astro-ph.EP↗
arXiv2026

RV$\times$TESS I: Modeling Asteroseismic Signals with Simultaneous Photometry and RVs

Detecting small planets via the radial velocity method remains challenged by signals induced by stellar variability, versus the effects of the planet(s). Here, we explore using Gaussian Process (GP) regression with Transiting Exoplanet Survey Satellite (TESS) photometry in modeling radial velocities (RVs) to help to mitigate stellar jitter from oscillations and granulation for exoplanet detection. We applied GP regression to simultaneous TESS photometric and RV data of HD 5562, a G-type subgiant ($M_\star=1.09M_{\odot}$, $R_\star=1.88R_{\odot}$) with a V magnitude of 7.17, using photometry to inform the priors for RV fitting. The RV data is obtained by the Magellan Planet Finder Spectrograph (PFS). The photometry-informed GP regression reduced the RV scatter of HD~5562 from 2.03 to 0.51 m/s. We performed injection and recovery tests to evaluate the potential of GPs for discovering small exoplanets around evolved stars, which demonstrate that the GP provides comparable noise reduction to the binning method. We also found that the necessity of photometric data depends on the quality of the RV dataset. For long baseline and high-cadence RV observations, GP regression can effectively mitigate stellar jitter without photometric data. However, for intermittent RV observations, incorporating photometric data improves GP fitting and enhances detection capabilities.

astro-ph.EP↗
arXiv2026

Testing Red Clump Models with the Asteroseismic Binary KIC 10841730

Binaries in which both stars are pulsating are rare but extremely valuable. We present the first study of an asteroseismic binary system consisting of a core helium-burning red clump (RC) star and a red giant branch (RGB) star. The Kepler target KIC 10841730 is a wide binary (period $2917 \pm 8$ d) that provides ideal conditions to test the accuracy of RC models. While prior studies of RC stars have revealed discrepancies in modelling the period spacings of mixed modes, other model parameters remain largely untested. We perform a detailed modelling analysis using individual mode frequencies and cover a large parameter space in mass, metallicity, He-abundance, mixing length, overshooting, and mass-loss, and we also explore different methods to correct for surface effects. We find two possible results for the red clump models. One solution requires introducing an unexpected offset of the phase shift in the red clump model, yielding an age consistent with the companion star and current masses of $1.01 \pm 0.06$ and $1.08 \pm 0.06$ M$_\odot$ for the RC and RGB star, respectively. Alternatively, we find that excluding the identification of two questionable radial modes resolves the phase-shift offset issue but results in a higher mass and thus a much younger age for the red clump star, contradicting the age obtained from its companion. We conclude that uncertainties in red clump models affect not only the g-mode period spacings but also the properties of the p modes. We show the power of asteroseismic binaries in validating and constraining stellar models and highlight the need for refining red-clump models.

astro-ph.SR↗
arXiv2025

A Test of Substellar Evolutionary Models with High-Precision Ages from Asteroseismology and Gyrochronology for the Benchmark System HR 7672AB

We present high-precision measurements for HR~7672AB, composed of a Sun-like (G0V) star and an L~dwarf companion. Three nights of precise (70 cm/s) radial velocity (RV) asteroseismology with the Keck Planet Finder clearly detect 5-minute oscillations from the primary HR~7672A, and modeling of the frequency spectrum yields an asteroseismic age of $1.87\pm0.65$~Gyr. We also determine a gyrochronological age of $2.58\pm0.47$~Gyr, and we combine these two results for a final age of $2.26\pm0.40$~Gyr. In addition, we obtained new RVs for HR~7672A and new astrometry for the companion HR~7672B. From a joint orbit fit, we measured a dynamical mass of $1.111\pm0.017$~$\text{M}_\odot$ for HR~7672A and $75.39\pm0.67$~$\text{M}_{\text{Jup}}$ for HR~7672B. This places the companion near the stellar/substellar boundary and thus particularly sensitive to differences in model predictions. The joint precision in host star age (18\% uncertainty) and companion mass (0.9\% uncertainty) makes HR~7672AB an exceptional substellar benchmark. Combined with the companion's luminosity, we use these measurements to test predictions from six brown dwarf cooling models. The best agreement occurs with the Chabrier et al. (2023) models, which incorporate a new equation of state, resulting in predictions that agree within $<$0.3$\sigma$ with all the observations. The other 5 sets of models agree at the 1--3$\sigma$ level depending on the particular test, and some models struggle to predict a sufficient low luminosity for HR~7672B at any age given its dynamical mass. We also detected a weak seismic signal in near-simultaneous TESS photometry of HR~7672A, with the resulting RV-to-photometry oscillation amplitude ratio consistent with solar values.

astro-ph.SR↗
arXiv2025

Discovery of 79 $\delta$ Scuti Stars in NGC 3532 Suggests a Decrease of Pulsator Occurrence with Age

Many A-F type stars do not display $\delta$ Scuti pulsations, despite being located within the instability strip. Open clusters provide a unique opportunity to study $\delta$ Scuti pulsations among coeval populations with uniform chemical composition. Here we use data from the TESS Mission to discover 79 $\delta$ Scuti pulsators in the 300 Myr old open cluster NGC 3532, the largest number found within a single open cluster to-date. We report a $50\pm5\%$ pulsator fraction in NGC 3532, considerably lower than in younger stellar populations, such the Pleiades (110 Myr), NGC 2516 (100 Myr), and the Cep-Her Complex ($\leq\,$80 Myr), and similar to the pulsator fraction found among field star samples. We introduce the concept of pulsator occurrence, which corrects for incompleteness, and find it to be $63\pm6\%$. For the stars that do pulsate, we find that the hotter stars occupy a distinct branch in the color-magnitude diagram (CMD) due to faster rotation ($>\,$150 km/s) than their non-pulsating counterparts. These results suggest that pulsator occurrence decreases with age and that rapid rotation is important in maintaining $\delta$ Scuti pulsations over time. We also investigate the Period-Luminosity (P-L) relation and the $\nu_{\rm max}$--$T_{\rm eff}$ relation of $\delta$ Scuti stars in NGC 3532. We find much scatter in the P-L relation of the dominant mode and two distinct branches in the $\nu_{\rm max}$--$T_{\rm eff}$ relation, similar to the Cep-Her Complex.

astro-ph.SR↗
arXiv2025

The highest mass Kepler red giants -- II. Spectroscopic parameters, the amplitude-activity relation, and unexpected halo orbits

The high-mass (M$>$2 \Msolar{}) Kepler red giant stars are less well-studied than their lower-mass counterparts. In the previous article, we presented a sample of 48 high-mass Kepler red giants and measured their asteroseismic parameters. This article presents spectroscopic measurements from the same sample, using high-resolution Keck/HIRES spectra to determine \Teff{}, [Fe/H], \logg{}, and $v \sin i$. We refined our previous estimates of the stellar masses and radii based on the new \Teff{}. We also examined spectral features that could indicate binary activity, such as the Li line and [C/N] ratios. We found no Li-rich stars or clear [C/N] anomalies, but we observed a correlation between [C/N] and [Fe/H]. We measured chromospheric activity using the $S$-index of the Ca II H \& K lines and found no correlation with internal magnetic fields. However, we confirmed an anti-correlation between surface chromospheric activity and radial mode oscillation amplitudes, which indicates that strong surface magnetic fields weaken stellar oscillations. Finally, we used the Gaia DR3 astrometric data to show that our sample of stars have orbits consistent with all three Galactic kinematic regions. Although these stars are quite young, their orbits carry them into the thick disk and even the halo, raising questions about the accuracy and viability of kinematics in unravelling Galactic history. In future work, we plan to use the spectroscopic parameters measured here to provide better constraints for boutique frequency modelling, which will allow us to test the asteroseismic scaling relations at the high-mass regime.

astro-ph.SR↗
arXiv2025

Luminaries in the Sky: The TESS Legacy Sample of Bright Stars. I. Asteroseismic detections in naked-eye main-sequence and sub-giant solar-like oscillators

We aim to detect and characterise solar-like oscillations in bright naked-eye (V<6) main-sequence (MS) and subgiant stars observed by TESS. We seek to expand the current benchmark sample of oscillators, provide accurate global asteroseismic parameters for these bright targets, and assess their potential for future detailed investigations -- including missions such as the HWO and PLATO. Our sample of bright stars was selected from the Hipparcos/Tycho catalogues. We analysed TESS 120-s and 20-s cadence photometry using SPOC light curves and custom apertures from target pixel files. After applying a filtering of the light curves, we extracted global asteroseismic parameters ($\nu_{\rm max}$ and $\Delta\nu$) using the pySYD pipeline. Results were cross-validated with independent pipelines and compared to predictions from the ATL, while noise properties were evaluated to quantify improvements from a 20-s observing cadence. We detect solar-like oscillations in a total of 196 stars -- including 128 new detections -- with extracted $\nu_{\rm max}$ and $\Delta\nu$ values showing strong conformity to expected scaling relations. This corresponds to an increase by more than an order of magnitude in the number of MS stars with detection of solar-like oscillations from TESS. Nearly 40% of our new detections are prime HWO targets, enabling systematic asteroseismic age determinations relevant for interpreting atmospheric biosignatures. Our analysis confirms that 20-s cadence data yields lower high-frequency noise levels compared to 120-s data. Moreover, the precise stellar parameters obtained through asteroseismology establish these bright stars as benchmarks for seismic investigations and provide useful constraints for refining stellar evolution models and for complementary analyses in interferometry, spectroscopy, and exoplanet characterisation.

astro-ph.SR↗
arXiv2025

The OATMEAL Survey. II. The 3D spin-orbit obliquity of an eccentric transiting brown dwarf in the Ruprecht 147 open cluster

We present new analysis of the CWW 89 system as part of the Orbital Architectures of Transiting Massive Exoplanets And Low-mass stars (OATMEAL) survey. The CWW 89 system is a member of the 2.8 Gyr old Ruprecht 147 (NGC 6774) cluster and features two stars, CWW 89A (EPIC 219388192) and CWW 89B, with the primary hosting a transiting brown dwarf. We use in-transit, highly precise radial velocity measurements with the Keck Planet Finder (KPF) to characterize the Rossiter-McLaughlin (RM) effect and measure the projected spin-orbit obliquity $|\lambda|=1.4\pm2.5^\circ$ and the full 3D spin-orbit obliquity of the brown dwarf to be $\psi=15.1^{+15.0^\circ}_{-10.9}$. This value of $\lambda$ implies that the brown dwarf's orbit is prograde and well-aligned with the equator of the host star, continuing the trend of transiting brown dwarfs showing a preference for alignment ($\lambda \approx 0^\circ$) regardless of the stellar effective temperature. We find that this contrast with the transiting giant planet population, whose spin-orbit alignments depend on host $T_{\rm eff}$, shows an increasingly clear distinction in the formation and orbital migration mechanisms between transiting giant planets and transiting brown dwarfs like CWW 89Ab. For this system in particular, we find it plausible that the brown dwarf may have undergone coplanar high-eccentricity migration influence by CWW 89B.

astro-ph.EP↗