arXiv subjects

Chenliang Huang

Publications and source records attributed to Chenliang Huang.

At least 19 recordsLinked to original sources

arXiv2026

Magrathea v2: A planetary interior modeling platform in C++

Magrathea is an open-source C++ code for modeling the internal structure of differentiated planets. The initial release, Huang et al. (2022), introduced the base solver, a modular framework for defining equations of state (EOS) within phase diagrams for each layer, and a plan for expanding the code. Many of those updates are now implemented. Magrathea v2 is a more versatile platform that supports a wider range of compositions, adds new tools for composition retrieval, and makes it easier for users to adapt the code to their own models.

astro-ph.IM↗

arXiv2026

The Garden of Forking Paths: Threading Narrative Archetype as a Semantic Signal Through Gameplay Planning

Generative models can produce individual game facets, but whole-game generation remains an orchestration problem: narrative, level structure, encounters, objectives, rewards, and visuals must express shared intent. We present Forking Garden, a branching game generation system that uses narrative archetype as a persistent semantic signal across the generation pipeline. Narrative progression is represented as soft Rise/Fall states; candidate plot nodes are generated before structural constraints assemble archetype-conforming graphs. The same state then conditions encounter composition, objectives, rewards, and runtime difficulty adaptation, while a shared symbolic schema preserves narrative entities and gameplay configurations through content instantiation. Across 10 storylines, generated paths exhibit distinguishable archetypal trajectories, narrative threat predicts damage taken by a threat-blind combat agent, and generate-first-constrain-later yields 2.6 times the entity diversity of a hierarchical baseline. A 16-participant study further suggests that propagated Rise/Fall distinctions can remain meaningful during play, while also supporting narrative understanding and creator-oriented interpretation.

cs.HC↗

arXiv2026

Hydrogen airglow from an escaping ultrahot Jupiter atmosphere

Intense high-energy irradiation of close-in gaseous exoplanets drives the rapid escape of their atmospheres, fundamentally shaping planetary demographics. While atmospheric loss is routinely observed via transit absorption in atomic hydrogen, helium, and metal ions, the underlying physical properties, specifically the thermal structure, outflow dynamics, and mass-loss rate, remain poorly constrained due to inherent degeneracies in the transmission geometry. Here we report the first detection of atomic hydrogen emission from the escaping atmosphere of a gas giant. Using high-resolution spectroscopy of the ultrahot Jupiter KELT-9 b, we detect a hydrogen Balmer line (Hα 6564.6 Å) emission signature originating from the planetary dayside. The emission line profile features a distinctive double-peaked shape with 0.1-0.15% peak amplitudes at +/-30 km/s and central self-absorption. This profile breaks transmission degeneracies, providing direct observational constraints on the vertical thermal structure, excited-state hydrogen populations, and wind dynamics in the upper atmosphere of KELT-9 b. Initial modeling reveals a vigorous outflow with a mass-loss rate above 10^{13} g/s, among the highest measured to date for gaseous exoplanets. Our results establish hydrogen airglow emission as a powerful diagnostic of atmospheric escape, opening a new observational window into the evolution of worlds in extreme radiation environments.

astro-ph.EP↗

arXiv2026

When Stars Mimic Monsters: Spectral Evidence for an $η$ Carinae-like Giant Eruption in SBS 0335$-$052 E

SBS 0335$-$052 E is an extremely low-metallicity ($Z\sim0.04\,Z_{\odot}$) blue compact dwarf galaxy. An active galactic nucleus has been proposed to explain the broad H$α$ emission and near-infrared (NIR) time variability in super star clusters 1 and 2 (SSCs 1&2). However, Peng et al. discovered broad wings in the forbidden [O III] $\lambda5007$ emission (up to $\sim5\,000\,\rm{km\,s^{-1}}$), challenging the broad-line region interpretation. We present new KCWI/KCRM integral-field spectroscopy to directly compare spectra across multiple SSCs. The nebula surrounding SSCs 1&2 shows unique features. The Ly$β$-pumped O I $\lambda8446$ emission constrains $τ_{\rm\,Lyα}\sim10^8$. Multiple ionization states of iron are detected from Fe$^{+}$ to Fe$^{+4}$. Stellar photoionization models can reproduce the [Fe III]/[Fe II] and [Fe IV]/[Fe III] line ratios at high density ($n_e\sim10^6\,\rm{cm^{-3}}$), but they fail to account for most of the [Fe V] emission. The broad H$α$ wings exhibit an exponential profile; the asymmetric wings extend from $\sim-5\,000\,\rm{km\,s^{-1}}$ to $\sim10\,000\,\rm{km\,s^{-1}}$. Thomson scattering in a radially expanding medium provides a good fit with $v_w\sim200\,\rm{km\,s^{-1}}$, optical depth $τ_e\sim10$, and an outer to inner radius of 10. Enhanced N/O and potentially depleted Fe/O ratios are consistent with CNO-cycled ejecta from massive stars and with dust formation, respectively. We propose that mass loss from a massive star interacting with its circumstellar medium drives a shock that powers the NIR variability, the luminous X-ray point source, and the [Fe V] emission. If confirmed, the proposed stellar eruption would be a distant example of an $η$ Carinae-like giant eruption, and the first in an ultra-low metallicity environment.

astro-ph.GA↗

arXiv2026

Helium escape in context: Comparative signatures of four close-in exoplanets

Observations of escaping atmospheres on close-in exoplanets show a wide range in the strength and morphology of He I 10830 A and H I absorption. Scaling relations attempt to link the He I signal to XUV irradiation, mass loss, and bulk planetary parameters. We test these relations with a comparative analysis of HD209458b, HD189733b, HD149026b, and GJ1214b using a 1D hydrodynamic, multi-species, full-atmosphere escape model. For the benchmark HD209458b, our previously validated solution reproduces the observed He I and Ha transit depths without imposing composition constraints. HD189733b exhibits comparable He I depths, but the broadest reported profiles require ~12 km/s of additional non-thermal broadening, whereas more recent measurements are narrower, consistent with our predictions. For HD149026b, despite similar system properties, our model shows that higher gravity suppresses escape and enhances diffusive separation, depleting helium at high altitudes and yielding extremely weak He I absorption. For the sub-Neptune GJ1214b, H/He-only models overestimate He I absorption; including H2 and its ions (H2+, H3+, HeH+) lowers the escape rate and modifies the ion/electron balance, reducing the metastable helium densities. Compared against scaling relations, HD189733b observations and our HD149026b prediction fall below the trend, whereas some observations of HD209458b and GJ1214b are consistent; however, the observed transit depths are variable. Across all targets, we find diffusive separation of helium and hydrogen, which may explain why sub-solar He/H ratios are often required in simplified models. We conclude that interpreting He I and Ha absorption requires first-principles models that include self-consistent temperature and velocity profiles, multi-species transport, and molecular chemistry.

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arXiv2025

All Stories Are One Story: Emotional Arc Guided Procedural Game Level Generation

The emotional arc is a universal narrative structure underlying stories across cultures and media -- an idea central to structuralist narratology, often encapsulated in the phrase "all stories are one story." We present a framework for procedural game narrative generation that incorporates emotional arcs as a structural backbone for both story progression and gameplay dynamics. Leveraging established narratological theories and large-scale empirical analyses, we focus on two core emotional patterns -- Rise and Fall -- to guide the generation of branching story graphs. Each story node is automatically populated with characters, items, and gameplay-relevant attributes (e.g., health, attack), with difficulty adjusted according to the emotional trajectory. Implemented in a prototype action role-playing game (ARPG), our system demonstrates how emotional arcs can be operationalized using large language models (LLMs) and adaptive entity generation. Evaluation through player ratings, interviews, and sentiment analysis shows that emotional arc integration significantly enhances engagement, narrative coherence, and emotional impact. These results highlight the potential of emotionally structured procedural generation for advancing interactive storytelling for games.

cs.AI↗

arXiv2025

A Multi-Species Atmospheric Escape Model with Excited Hydrogen and Helium: Application to HD209458b

Atmospheric escape shapes exoplanet evolution and star-planet interactions, with He I 10830 Å absorption serving as a key tracer of mass loss in hot gas giants. However, transit depths vary significantly across observed systems for reasons that remain poorly understood. HD209458b, the archetypal hot-Jupiter, exhibits relatively weak He I 10830 Å and H$α$ absorption, which has been interpreted as evidence for a high H/He ratio (98/2), possibly due to diffusive separation. To investigate this possibility and other processes that control these transit depths, we reassess excitation and de-excitation rates for metastable helium and explore the impact of diffusion processes, stellar activity, and tidal forces on the upper atmosphere and transit depths using a model framework spanning the whole atmosphere. Our model reproduces the observed He I transit depth and H$α$ upper limit, showing strong diffusive separation. We match the observations assuming a photoelectron efficiency of 20-40\%, depending on the composition of the atmosphere, corresponding to mass-loss rates of $1.9-3\times10^{10}$ g/s. We find that the He I 10830 Å transit depth is sensitive to both stellar activity and diffusion processes, while H$α$ is largely unaffected due to its strong dependence on Lyman-$α$ excitation. These differences may help explain the system-to-system scatter seen in population-level studies of the He I line. While He I data alone may not tightly constrain mass-loss rates or temperatures, they do confirm atmospheric escape and help narrow the viable parameter space when interpreted with physically motivated models. Simultaneous observations of He I, H$α$, and stellar activity indicators provide powerful constraints on upper atmosphere dynamics and composition, even in the absence of full transmission spectra.

astro-ph.EP↗

arXiv2025

Uncertainties in the Inference of Internal Structure: The Case of TRAPPIST-1 f

We use the TRAPPIST-1 system as a model observation of Earth-like planets. The densities of these planets being 1-10% less than the Earth suggest that the outer planets may host significant hydrospheres. We explore the uncertainty in water mass fraction from observed mass and radius. We investigate the interior structure of TRAPPIST-1 f using the open-source solver MAGRATHEA and varying assumptions in the interior model. We find that TRAPPIST-1 f likely has a water mass fraction of 16.2% $\pm$ 9.9% when considering all possible core mass fractions and requires 6.9% $\pm$ 2.0% water at an Earth-like mantle to core ratio. We quantify uncertainties from observational precision, model assumptions, and experimental and theoretical data on the bulk modulus of planet building materials. We show that observational uncertainties are smaller than model assumptions of mantle mineralogy and core composition but larger than hydrosphere, temperature, and equation of state assumptions/uncertainties. Our findings show that while precise mass and radius measurements are crucial, uncertainties in planetary models can often outweigh those from observations, emphasizing the importance of refining both theoretical models and experimental data to better understand exoplanet interiors.

astro-ph.EP↗

arXiv2025

CoKnowledge: Supporting Assimilation of Time-synced Collective Knowledge in Online Science Videos

Danmaku, a system of scene-aligned, time-synced, floating comments, can augment video content to create 'collective knowledge'. However, its chaotic nature often hinders viewers from effectively assimilating the collective knowledge, especially in knowledge-intensive science videos. With a formative study, we examined viewers' practices for processing collective knowledge and the specific barriers they encountered. Building on these insights, we designed a processing pipeline to filter, classify, and cluster danmaku, leading to the development of CoKnowledge - a tool incorporating a video abstract, knowledge graphs, and supplementary danmaku features to support viewers' assimilation of collective knowledge in science videos. A within-subject study (N=24) showed that CoKnowledge significantly enhanced participants' comprehension and recall of collective knowledge compared to a baseline with unprocessed live comments. Based on our analysis of user interaction patterns and feedback on design features, we presented design considerations for developing similar support tools.

cs.HC↗

arXiv2024

PEPSI's non-detection of escaping hydrogen and metal lines adds to the enigma of WASP-12 b

WASP-12 b is an ultra-hot Jupiter (UHJ) of special interest for atmospheric studies since it is on an inspiraling orbit in an extreme environment of intense radiation and circumstellar gas. Previously claimed detections of active mass loss from this planet are controversial across the literature. To address this controversy, we obtain two new transit observations of WASP-12 b with the optical high-resolution PEPSI spectrograph on the Large Binocular Telescope. Contrary to previous work, we do not observe planetary H$α$ absorption and rule out the amplitude of previously reported detections. Our non-detection may be limited by the sensitivity of our data or could indicate weaker mass loss than suggested by previous studies. We conduct injection-recovery experiments to place constraints on the radial extent of WASP-12 b's escaping atmosphere as probed by Balmer lines, but find that our data do not have the sensitivity to probe down to the planet's Roche Lobe. Using physically motivated models of atmospheric escape, we explore upper limit constraints on the planet's mass-loss rate and deem the data quality in the wavelength regime of Balmer lines insufficient to determine a physically meaningful constraint. We also conduct a spectral survey of other optical absorbers to trace atmospheric circulation but detect no additional absorption. We conclude that previous claims of H$α$ absorption from the atmosphere of WASP-12 b should be reevaluated. Given the anticipated line strength of Balmer/optical features, observing the atmosphere of this faint target will require stacking more observations even with the largest telescope facilities available.

astro-ph.EP↗

arXiv2023

CUTE reveals escaping metals in the upper atmosphere of the ultra-hot Jupiter WASP-189b

Ultraviolet observations of Ultra-hot Jupiters (UHJs), exoplanets with temperatures over 2000\,K, provide us with an opportunity to investigate if and how atmospheric escape shapes their upper atmosphere. Near-ultraviolet transit spectroscopy offers a unique tool to study this process owing to the presence of strong metal lines and a bright photospheric continuum as the light source against which the absorbing gas is observed. WASP-189b is one of the hottest planets discovered to date, with a day-side temperature of about 3400\,K orbiting a bright A-type star. We present the first near-ultraviolet observations of WASP-189b, acquired with the Colorado Ultraviolet Transit Experiment ($CUTE$). $CUTE$ is a 6U NASA-funded ultraviolet spectroscopy mission, dedicated to monitoring short-period transiting planets. WASP-189b was one of the $CUTE$ early science targets and was observed during three consecutive transits in March 2022. We present an analysis of the $CUTE$ observations and results demonstrating near-ultraviolet (2500--3300~Å) broadband transit depth ($1.08^{+0.08}_{-0.08}\%$) of about twice the visual transit depth indicating that the planet has an extended, hot upper atmosphere with a temperature of about 15000\,K and a moderate mass loss rate of about \SI{4e8}{\kg\per\second}. We observe absorption by Mg{\sc ii} lines ($R_p/R_s$ of $0.212^{+0.038}_{-0.061}$) beyond the Roche lobe at $>$4$σ$ significance in the transmission spectrum at a resolution of 10~Å, while at lower resolution (100~Å), we observe a quasi-continuous absorption signal consistent with a "forest" of low-ionization metal absorption dominated by Fe{\sc ii}. The results suggest an upper atmospheric temperature ($\sim15000$\,K), higher than that predicted by current state-of-the-art hydrodynamic models.

astro-ph.EP↗

arXiv2023

A hydrodynamic study of the escape of metal species and excited hydrogen from the atmosphere of the hot Jupiter WASP-121b

In the near-UV and optical transmission spectrum of the hot Jupiter WASP-121b, recent observations have detected strong absorption features of Mg, Fe, Ca, and H$α$, extending outside of the planet's Roche lobe. Studying these atomic signatures can directly trace the escaping atmosphere and constrain the energy balance of the upper atmosphere. To understand these features, we introduce a detailed forward model by expanding the capability of a one-dimensional model of the upper atmosphere and hydrodynamic escape to include important processes of atomic metal species. The hydrodynamic model is coupled to a Ly$α$ Monte Carlo radiative transfer calculation to simulate the excited hydrogen population and associated heating/ionization effects. Using this model, we interpret the detected atomic features in the transmission spectrum of WASP-121b and explore the impact of metals and excited hydrogen on its upper atmosphere. We demonstrate the use of multiple absorption lines to impose stronger constraints on the properties of the upper atmosphere than the analysis of a single transmission feature can provide. In addition, the model shows that line broadening due to atmospheric outflow driven by the Roche lobe overflow is necessary to explain the observed line widths and highlights the importance of the high mass-loss rate caused by the Roche lobe overflow that requires careful consideration of the structure of the lower and middle atmosphere. We also show that metal species and excited state hydrogen can play an important role in the thermal and ionization balance of ultra-hot Jupiter thermospheres.

astro-ph.EP↗

arXiv2023

The Hubble/STIS Near-ultraviolet Transmission Spectrum of HD 189733b

The benchmark hot Jupiter HD 189733b has been a key target to lay out the foundations of comparative planetology for giant exoplanets. As such, HD 189733b has been extensively studied across the electromagnetic spectrum. Here, we report the observation and analysis of three transit light curves of HD 189733b obtained with {\Hubble}/STIS in the near ultraviolet, the last remaining unexplored spectral window to be probed with present-day instrumentation for this planet. The NUV is a unique window for atmospheric mass-loss studies owing to the strong resonance lines and large photospheric flux. Overall, from a low-resolution analysis ($R=50$) we found that the planet's near-ultraviolet spectrum is well characterized by a relatively flat baseline, consistent with the optical-infrared transmission, plus two regions at $\sim$2350 and $\sim$2600 Å that exhibit a broad and significant excess absorption above the continuum. From an analysis at a higher resolution ($R=4700$), we found that the transit depths at the core of the magnesium resonance lines are consistent with the surrounding continuum. We discarded the presence of \ion{Mg}{ii} absorption in the upper atmosphere at a $\sim$2--4$σ$ confidence level, whereas we could place no significant constraint for \ion{Mg}{i} absorption. These broad absorption features coincide with the expected location of \ion{Fe}{ii} bands; however, solar-abundance hydrodynamic models of the upper atmosphere are not able to reproduce the amplitude of these features with iron absorption. Such scenario would require a combination of little to no iron condensation in the lower-atmosphere, super-solar metallicities, and a mechanism to enhance the absorption features (such as zonal wind broadening). The true nature of this feature remains to be confirmed.

astro-ph.EP↗

arXiv2022

MAGRATHEA: an open-source spherical symmetric planet interior structure code

MAGRATHEA is an open-source planet structure code that considers the case of fully differentiated spherically symmetric interiors. Given the mass of each layer and the surface temperature, the code iterates the boundary conditions of the hydrostatic equations using the method of shooting to a fitting point in order to find the planet radius. The first version of MAGRATHEA supports a maximum of four layers of iron, silicates, water, and ideal gas. With a few exceptions, the temperature profile can be chosen between isothermal, isentropic, and user-defined functions. The user has many options for the phase diagram and equation of state in each layer and we document how to add additional equations of state. We present MAGRATHEA's capabilities and discuss its applications. We encourage the community to participate in the development of MAGRATHEA at https://github.com/Huang-CL/Magrathea.

astro-ph.EP↗

arXiv2022

Mass loss by atmospheric escape from extremely close-in planets

We explore atmospheric escape from close-in exoplanets with the highest mass loss rates. First, we locate the transition from stellar X-ray and UV-driven escape to rapid Roche lobe overflow, which occurs once the 10-100 nbar pressure level in the atmosphere reaches the Roche lobe. Planets enter this regime when the ratio of the substellar radius to the polar radius along the visible surface pressure level, that aligns with a surface of constant Roche potential, is X/Z~$\gtrsim$~1.2 for Jovian planets (Mp~$\gtrsim$~100 M$_{\Earth}$) and X/Z~$\gtrsim$~1.02 for sub-Jovian planets ($M_p \approx$~10--100 M$_{\Earth}$). Around a sun-like star, this regime applies to orbital periods of less than two days for planets with radii of about 3--14 R$_{\Earth}$. Our results agree with the properties of known transiting planets and can explain parts of the sub-Jovian desert in the population of known exoplanets. Second, we present detailed numerical simulations of atmospheric escape from a planet like Uranus or Neptune orbiting close to a sun-like star that support the results above and point to interesting qualitative differences between hot Jupiters and sub-Jovian planets. We find that hot Neptunes with solar metallicity hydrogen and helium envelopes have relatively more extended upper atmospheres than typical hot Jupiters, with a lower ionization fraction and higher abundances of escaping molecules. This is consistent with existing ultraviolet transit observations of warm Neptunes and it might provide a way to use future observations and models to distinguish solar metallicity atmospheres from higher metallicity atmospheres.

astro-ph.EP↗

arXiv2021

H-Alpha Variability of V1298 Tau c

The 23 Myr system V1298 Tau hosts four transiting planets and is a valuable laboratory for exploring the early stages of planet evolution soon after formation of the star. We observe the innermost planet, V1298 Tau c, during transit using LBT PEPSI to obtain high spectral resolution characterization of escaping material near the H-alpha line. We find no strong evidence for atmospheric material escaping at the orbital velocity of the planet. Instead, we find a deep stellar feature that is variable on the few percent level, similar to a previous observation of the planet and can be explained by stellar activity. We attempted to monitor the broadband optical transit with LBT MODS but do not achieve the precision needed to characterize the atmosphere or improve the ephemeris.

astro-ph.EP↗

arXiv2021

Implications of an improved water equation of state for water-rich planets

Water (H$_{2}$O), in all forms, is an important constituent in planetary bodies, controlling habitability and influencing geological activity. Under conditions found in the interior of many planets, as the pressure increases, the H-bonds in water gradually weaken and are replaced by ionic bonds. Recent experimental measurements of the water equation of state (EOS) showed both a new phase of H-bonded water ice, ice-VII$_t$, and a relatively low transition pressure just above 30 GPa to ionic bonded ice-X, which has a bulk modulus 2.5 times larger. The higher bulk modulus of ice-X produces larger planets for a given mass, thereby either reducing the atmospheric contribution to the volume of many exoplanets or limiting their water content. We investigate the impact of the new EOS measurements on the planetary mass-radius relation and interior structure for water-rich planets. We find that the change in the planet mass-radius relation caused by the systematic differences between previous and new experimental EOS measurements are comparable to the observational uncertainties in some planet sizes -- an issue that will become more important as observations continue to improve.

astro-ph.EP↗

arXiv2021

Atmosphere escape inferred from modelling the H$α$ transmission spectrum of WASP-121b

The escaping atmospheres of hydrogen driven by stellar X-ray and extreme Ultraviolet (XUV) have been detected around some exoplanets by the excess absorption of Ly$α$ in far ultraviolet band. In the optical band the excess absorption of H$α$ is also found by the ground-based instruments. However, it is not certain so far if the escape of the atmosphere driven by XUV can result in such absorption. Here we present the XUV driven hydrodynamic simulation coupled with the calculation of detailed level population and the process of radiative transfer for WASP-121b. Our fiducial model predicts a mass loss rate of $\sim$1.28$\times$10$^{12}$g/s for WASP-121b. Due to the high temperature and Ly$α$ intensity predicted by the fiducial model, many hydrogen atoms are populated into the first excited state. As a consequence, the transmission spectrum of H$α$ simulated by our model is broadly consistent with the observation. Comparing with the absorption of H$α$ at different observation times, the stellar XUV emission varies in the range of 0.5-1.5 times fiducial value, which may reflect the variation of the stellar activity. Finally, we find that the supersonic regions of the planetary wind contribute a prominent portion to the absorption of H$α$ by comparing the equivalent width of H$α$, which hints that a transonic outflow of the upper atmosphere driven by XUV irradiation of the host star can be detected by the ground-based telescope and the H$α$ can be a good indicator of escaping atmosphere.

astro-ph.EP↗