arXiv subjects

Daniel Apai

Publications and source records attributed to Daniel Apai.

At least 19 recordsLinked to original sources

arXiv2026

A Model to Map Brown Dwarf Companions to White Dwarfs in Partial Secondary Eclipse

Eclipse mapping is a well-established technique for constraining the spatial emission of hot Jupiter exoplanets. Brown dwarfs in ultra-short orbits around white dwarfs are an analog to hot Jupiters that can only ever be eclipsed within a limited range of latitudes. We adapt the eigenmapping method to disentangle the signals from the ever- and never-occulted regions. The result of this signal separation is a super-position of map structures, yielding sharp boundaries at the occultation region. We introduce a model that penalizes the harmonic complexity of the model map with Tikhonov regularization, whose parameters are tuned to reproduce the fit quality of the eigenmapping model. We use JWST NIRSpec/PRISM full-orbit observations of the eclipsing WD 1202-024 system as a template to construct and run injection-recovery tests on simulated light curves, isolating both latitudinal structures as well as emission from a physically-realistic general circulation model (GCM). In the latter, the narrow equatorial jet driven by the BD's rapid rotation manifests as an eclipse depth asymmetry, which our model reproduces as a latitude-dependent phase offset. Such a model, however, is only statistically preferred at approximately $3 \times$ the signal-to-noise ratio of the JWST data. When fitting to the actual JWST data of WD 1202, the full-phase eigenbasis model is statistically preferred. However, the resulting model map of WD 1202 B does not resemble the GCM predictions, with a concentrated day-side hotspot at the sub-stellar point with an angular size $\approx 15^\circ$. Interpreting this result more carefully requires follow-up work to disentangle systematics from true emission signals. This model framework provides a means to detect emission features from these rare types of eclipses, and ultimately to test predictions of models of atmospheric circulation across hot Jupiters and their BD analogs.

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arXiv2026

Magnetic Activity as a Driver of Low-gravity-like Spectral Morphology in Late-M Dwarfs

We present a systematic investigation of the connection between magnetic activity and the low-surface-gravity-like near-infrared spectral morphology of late-M dwarfs. Our sample includes TRAPPIST-1 observed with JWST NIRISS/SOSS and 22 late-M dwarfs observed with IRTF/SpeX, together with flare observations from K2, TESS, JWST NIRISS/SOSS, and literature-reported X-ray luminosities. Using one-component PHOENIX/NewEra spectral modeling, we find that all targets are better reproduced by lower-surface-gravity model spectra than by models with the expected high gravities of field late-M dwarfs. The retrieved surface gravities moderately correlate with independently measured gravity-sensitive spectral indices, with the strongest trends seen for FeH$_z$ at 0.998~$μ$m and FeH$_J$ at 1.2~$μ$m, both showing statistically significant Pearson and Spearman correlations with $p<0.005$. They also show strong anti-correlations with flare luminosity and X-ray luminosity: for both relations, Pearson and Spearman coefficients are $<-0.9$, with $p \leq 1.0\times10^{-4}$, indicating that more active stars tend to have spectra favoring lower-gravity morphologies. Time-series spectra of TRAPPIST-1 during two large flares show no clear short-timescale variations in selected photospheric indices, suggesting that persistent small-scale magnetic activity may play a more important role than large flares in modifying the photospheric temperature--pressure structure. A simplified radiative-transfer experiment further shows that activity-associated heating can produce lower-gravity-like spectral features even when the input surface gravity is fixed. Our results suggest that underestimated surface gravities in late-M dwarfs may reflect atmospheres modified by frequent, small-scale magnetic activity, such as microflares, producing emergent spectra that mimic lower-gravity morphology.

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arXiv2026

Asymmetric nightside CO2 features, inefficient heat transport, and precise evolutionary constraints: Spectroscopic phase curves reveal the past and present of a white dwarf-brown dwarf binary

We present the first JWST phase curve of a white dwarf-brown dwarf binary, a NIRSpec PRISM observation of ZTFJ0038+2030. Short-period white dwarf-brown dwarf binaries provide unique laboratories to probe substellar atmospheres. Tidal locking drives hot Jupiter-like atmospheric dynamics in the brown dwarf. The system's formation history offers a window into planetary systems around post-main-sequence stars. We obtain a full-orbit phase curve of ZTF0038, including a total eclipse of the white dwarf, which enables us to separate the two components' emission throughout the entire orbit, and we model the brown dwarf's phase-resolved emission spectra using substellar atmosphere forward models and atmospheric retrievals. The PRISM spectrum covers ~80% of the brown dwarf's bolometric emission, enabling a nearly model-independent energy balance calculation, which yields a day-to-nightside heat transport efficiency of <10%. Inefficient heat redistribution is further supported by the phase curve shape and the nightside spectrum closely resembling non-irradiated mid-to-late T dwarfs. The spectroscopic phase curves reveal a stark nightside asymmetry associated with a strong CO2 absorption feature at 4.2 um, while the retrieved abundances indicate a longitudinally homogeneous distribution of CO2 as well as all other key species detected in the atmosphere. The precise internal luminosity measurement of the brown dwarf informs both the age of the WD-BD system (7.5-8.8 Gyr) and indicates a low common-envelope ejection efficiency. These data illustrate the exquisite opportunity to probe the three-dimensional processes of substellar atmospheres, connect substellar and exoplanet atmospheres, and probe the evolution of post-main-sequence planetary systems using WD-BDs.

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arXiv2026

Deep HST/STIS Coronagraphic Imaging of the $β$ Pictoris Debris Disk: On the Scattered Light Component of the Cat's Tail

The $β$ Pictoris debris disk is a unique system where mid-infrared coronagraphic imaging with JWST/MIRI revealed a new spatially resolved substructure known as the Cat's Tail. We present deep HST/STIS coronagraphic imaging of $β$ Pic in scattered light, combining six epochs of observations between 2012 and 2025, in search of the scattered light component of the Cat's Tail. We detect the disk out to a projected separation of 500 au for the first time with HST/STIS, achieving SNR > 100 across much of the midplane between 50 and 200 au. We report the detection of the visible/near-infrared scattered light component of the Cat's Tail substructure. We find through injection-recovery analysis that the scattered light component of the Cat's Tail has a total flux of $0.1-0.4\%$ of the MIRI F1550C flux. Using the measured STIS-to-MIRI flux ratio, we model the Cat's Tail grain properties and find that the grains are highly porous and almost entirely composed of organic refractory material, which is in agreement with findings with JWST/MIRI. We use the organics content of Solar System dwarf planets and dust in the local ISM as a proxy to estimate the size of the colliding progenitors that can produce enough organic refractory material seen in the Cat's Tail. We find that each colliding progenitor must have a mass of at least $1-3\times 10^{21}$ kg, comparable to Charon and Makemake in our Kuiper Belt. Additionally, we find a prominent warped morphology and surface brightness asymmetry in the outer dust halo of $β$ Pic. We compare the observed halo morphology and asymmetry to predicted vertical structures, which may arise from planet--disk interactions.

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arXiv2026

Super-Earth Interiors Shrink by About 10% as They Crystallise

Super-Earth exoplanets are among the most abundant planets known, yet their bulk densities leave the interior state degenerate. The static structure models used to interpret them, and the interior retrievals built on them, typically describe the cold, solidified end state of an evolution that begins hot and molten. During this magma ocean stage the interior, the outgassed atmosphere, and the surface co-evolve and set the long-term climate and geophysics of super-Earths. We develop and validate a fully coupled model for the structural and thermal evolution of super-Earth exoplanets within the PROTEUS framework, including new and upgraded models of the interior structure, mantle energetics, and volatile outgassing. In volatile-poor super-Earths of 1 to 10 Earth masses, the silicate interior contracts by about 10 % of its molten radius through cooling and crystallisation, nearly independent of planet mass and driven by the thinning silicate shell alone. The solidified radius is set by planetary mass and core fraction, insensitive to the host star, irradiation, and initial thermal state. In contrast, volatile-rich super-Earths at and above about 5 Earth masses may not solidify: their thick outgassed atmospheres throttle the surface heat loss until the interior settles into a deep magma ocean, keeping the planet inflated and limiting the contraction to about half its volatile-poor value. Mantle contraction alone thus shapes the low-mass exoplanet transit population, motivating joint interpretation of atmospheric and geophysical signatures in upcoming exoplanet surveys.

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arXiv2026

Multi-Epoch Stability in the Rotational Modulation of the Planetary-Mass Companion Ross 458C

Spectroscopic variability is detected in brown dwarfs across all spectral types, suggesting atmospheric patchiness in brown dwarf atmospheres. We present JWST/NIRSpec time series observations of the T8.0 planetary-mass companion Ross 458C. We compared our derived spectral variability and light curve to those obtained using HST/WFC3 observations more than 7.5 yr before and published by Manjavacas et al. (2019). We found that the light curve of Ross 458C is remarkably similar in the two epochs in terms of shape and variability amplitude potentially created by stable weather patterns. We measured a rotational period of 11.57+\-0.09 hr, demonstrating that the previously reported HST/WFC3 period of 6.75+\-1.58 hr is most likely a second-order harmonic produced by an unresolved double-peaked rotational modulation, likely due to the higher uncertainties of the HST/WFC3 light curve and the short time baseline of those observations. We measured the variability amplitude in the white light curve created using only the wavelength range covered by HST/WFC3 (1.10-1.63 micron), obtaining a value of 1.47+\-0.18%, which is consistent with that measured in the HST/WFC3 light curve.

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arXiv2026

A Grid of Contribution Functions to Help the Interpretation of Time-resolved Observations of Brown Dwarfs

We present a grid of thermal emission contribution functions and their corresponding atmospheric spectra model for cloudy and cloud-free brown dwarfs, spanning effective temperatures $T_{\rm eff} \in [500, 2000]$ K, surface gravities $\log g = [3.5, 5.5]$ [cgs], sedimentation efficiencies $f_{\rm sed} = 1, 2, 3, 4$ and 8, and eddy diffusion coefficients $\log K_{\rm zz} = [6, 11]$. We use temperature-pressure profiles from the Sonora Diamondback models in conjunction with the picaso radiative transfer code and the cloud modeling code virga, to explore how different atmospheric parameters influence the vertical distribution of emitted radiation for atmospheres in chemical equilibrium. We confirm that cloud opacity significantly impacts atmospheric emission depth in prominent molecular features such as CH$_4$, H$_2$O, CO, NH$_3$, CO$_2$, and atomic features Na and K. The atmospheric emission depth varies most notably in the $J$-band, and at mid-resolution spectra in the Na and K doublets. Our analysis highlights pressure-wavelength differences between cloudy and cloud-free atmospheres for characterizing L, L/T transition, and T-type brown dwarfs and demonstrates how contribution functions can guide targeted spectroscopic investigations. To facilitate observational planning, we provide an accessible database and web-based application that enable the community to compare observational data with our model grid of spectra and contribution functions with a wavelength range of 0.5 - 30 $μ$m.

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arXiv2026

The Interstellar Laser Beacons Hypothesis and the Cosmic Lighthouses Project

In this paper, we argue that in a realistic, resource-limited scenario senders whose intent is to maximize successful communication at the lowest cost will utilize very long-lived, pulsed beacons. Further, we argue that mass-producible laser beacons with simpler technology ($μ$s or ms pulses instead of ultrashort fs pulses) are more optimal if placed on interstellar orbits. Our extensive, existing surveys are mostly blind to the $μ$s/ms-second universe and to such beacons. We show, however, that the convergence of three technologies (massively parallel processing, ultra high-speed CMOS detectors, and broadband, mass-producible diffractive-refractive lenses) now offer an exciting opportunity for a low-cost survey of the $μ$second sky. Such survey would be astrophysically compelling and, with even low-cost telescopes, could place volume-complete constraints on interstellar beacons within twenty parsecss.

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arXiv2026

Mapping Stellar Heterogeneities with the Nautilus Space Observatory

Stellar photospheric heterogeneities, such as starspots and faculae, are a fundamental limitation for exoplanet transmission spectroscopy. Inhomogeneous surfaces can imprint wavelength-dependent signals during transits that may mimic or mask atmospheric absorption features, especially for planets orbiting cool low-mass stars. Recent work has shown that the information content of transmission spectroscopy observations can be sufficient to correct for stellar contamination, but only if stellar photosphere and active-region models have adequate fidelity. This requires empirical benchmarking with observations that validate next-generation stellar models and identify which spectral diagnostics best encode heterogeneity properties as a function of spectral type, activity level, and time. We propose a two-generation Nautilus program that leverages the scalable architecture of the observatory concept. Generation 1 would use broad-wavelength time-series observations of transiting exoplanet systems to connect starspot-crossing events and out-of-transit variability to localized and disk-integrated heterogeneity properties. Generation 2 would use the optimized spectral diagnostics identified in Generation 1 to conduct slitless spectroscopic monitoring of large samples of GKM stars on different timescales. Generation 2 instrumentation would include activity tracers of both the photosphere and chromosphere. This program would provide the benchmark data and population-level framework needed to turn stellar contamination into a calibrated input for exoplanet atmospheric retrievals.

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arXiv2026

Nautilus Space Observatory: The Evolution of Planets and their Atmospheres

We are just beginning to explore the billion-year evolution from nascent planets in disks to mature planetary systems. Recent discoveries hint at demographic and atmospheric differences between young planets and their Gyr-old counterparts, but current facilities are limited - particularly in their ability to conduct statistical atmospheric studies over a broad period range. This white paper outlines compelling science achievable with the Nautilus Space Observatory, a proposed constellation of large-diameter space telescopes. We identify four primary scientific objectives: (1) determining the timescales over which planets evolve into sub-Neptunes and super-Earths; (2) tracking the temporal evolution of atmospheric mass-loss rates; (3) characterizing the evolution of the atmospheric mean molecular weight and C/O ratio; and (4) identifying the emergence of Helium-dominated worlds. Answering these questions requires the high spatial resolution, broad-wavelength coverage, large effective area, and parallelized multiple units that Nautilus provides. By isolating the physical processes that govern the evolution of planets and their atmospheres, these science objectives directly support NASA's Cosmic Origins and Exoplanet Exploration Programs.

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arXiv2026

A single power law for the TRAPPIST-1 flare distribution across four orders of magnitude in energy

TRAPPIST-1 is an ultra-cool dwarf that flares frequently. These flares shape the surrounding planets' high-energy irradiation environments, with consequences for atmospheric chemistry and escape, and they can contaminate transmission spectroscopy of those planets. A quantitative flare-frequency distribution (FFD) spanning the full energy range is therefore essential for both interpreting JWST spectra and modeling the planets' irradiation histories. Here we present a unified FFD over four orders of magnitude in energy by jointly analyzing $\approx$87\,hr of JWST/NIRISS and JWST/NIRSpec time-series spectroscopy together with $\approx$74\,days of \textit{Kepler}/K2 photometry. To enable a consistent comparison across these heterogeneous datasets, we convert all events to energies in the TESS bandpass. For the Kepler-to-TESS conversion we adopt a cooler flare continuum appropriate for ultra-cool dwarfs ($T_{\rm flare}=3500$\,K). After correcting for flare-detection sensitivities, the combined JWST+K2 cumulative FFD is consistent with a single power law, $N(\ge E_\mathrm{TESS})\propto E_\mathrm{TESS}^{-β}$, with $β=0.753$ over $E_{\rm TESS}\simeq10^{29}$-$10^{33}$\,erg. The slope of the distribution indicates that the time-averaged flare energy budget is dominated by rare, high-energy events rather than by the more numerous low-energy flares. Moreover, we found that strong flares with energies $E_\mathrm{TESS} > 10^{32}$~erg occur once every 25 days, about an order of magnitude more frequently than inferred from previous TRAPPIST-1/analog FFD estimates. This elevated rate of energetic flares has important implications for atmospheric escape, photochemistry, and habitability assessments of the TRAPPIST-1 planets.

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arXiv2026

Unlocking HST's Stellar Treasure Trove: Stellar Activity Minima for HAT-P-11 Offer Prime Windows for Transmission Spectroscopy

HAT-P-11 is a well-studied, active K dwarf hosting an eccentric, misaligned transiting sub-Neptune. As part of the HST Stellar Treasure Trove program (HST-AR-17551), we analyze absolutely calibrated out-of-transit \HST{} spectra from \texttt{STIS} and \texttt{WFC3} across the \textsc{G430L}, \textsc{G750L}, \textsc{G102}, and \textsc{G141} bandpasses to constrain the surface heterogeneity of HAT-P-11 and its impact on transmission spectroscopy. Grid-based spectral retrievals using NewEra \texttt{PHOENIX} models robustly favor two-component photospheres in the \texttt{WFC3} G102 and G141 data, with a ${\sim}4950$\,K photospheric component and a cooler ($\sim$3400\,K) component covering 26{--}33\% of the stellar disk. By contrast, retrievals on the \texttt{STIS} optical spectra do not yield a satisfactory fit, reflecting current limitations of stellar atmosphere models in the optical regime compared to the \HST{} observational precision. We contextualize these results using long-term photometric monitoring and chromospheric activity indices. The inferred high spot covering fractions are broadly consistent with the elevated photometric variability observed during the \textit{Kepler} era ($f_{\rm spot}$$\sim$10--20\%) but are in tension with the much lower rotational amplitudes observed from TESS in the mid 2020s ($f_{\rm spot}$$\sim$1--10\%). This secular decline in variability is mirrored by a $\sim$20\% decrease in the Ca\,\textsc{ii} H\&K index. These results imply that HAT-P-11 undergoes comparatively quiescent phases that offer more favorable windows for atmospheric characterization, which serendipitously coincided with some of the recent JWST observations. More generally, our study demonstrates that multi-epoch, space-based stellar spectra provides a physically grounded pathway for mitigating stellar contamination in high-precision transmission spectra in the JWST era.

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arXiv2026

NASA's Pandora SmallSat Mission: Simulated Modeling and Retrieval of Near-Infrared Exoplanet Transmission Spectra

Pandora is a SmallSat mission dedicated to understanding exoplanets and their host stars by disentangling the impact of stellar heterogeneity on exoplanet transmission spectra. Selected as a NASA Astrophysics Pioneers mission in 2021, Pandora will provide simultaneous long-term visible photometric monitoring (0.4--0.7 $μ$m) and low-resolution near-infrared (NIR) spectroscopy (0.9--1.6 $μ$m) of transiting systems for the purposes of monitoring host star variability and characterizing exoplanetary atmospheres. Pandora's year-long prime mission from 2026 to 2027 coincides with the middle of a decade defined by targeted efforts for atmospheric characterization of exoplanets, offering a key opportunity to leverage this new resource to maximize science with JWST and other observatories. Here we investigate Pandora's anticipated performance for the general exoplanet population accessible to transit spectroscopy, from hot Jupiters to temperate sub-Neptunes. By modeling the atmospheres of five test cases broadly consistent with the bulk properties of HD~209458~b, HD~189733~b, WASP-80~b, HAT-P-18~b, and K2-18~b, we find that Pandora may provide abundance constraints as precise as $\sim$1.0\,dex for main atmospheric absorbers such as H$_2$O and CH$_4$. Then, we explore the synergies between Pandora and JWST. Our results suggest that targets with JWST data in the near-infrared can benefit from the addition of Pandora observations and result in more reliable abundance estimates than with JWST data alone. Moreover, Pandora can serve the community by providing precursory observations of targets of interest for JWST atmospheric characterization. We conclude by outlining strategies for the use of Pandora as a standalone observatory and in synergy with JWST.

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arXiv2025

Characterizing the Time Variability of 2M1207 A+b with JWST NIRSpec/PRISM

We present JWST NIRSpec/PRISM IFU time-resolved observations of 2M1207 A and b (TWA 27), a $\sim 10$ Myr binary system consisting of a $\sim 2500$ K sub-stellar primary hosting a $\sim 1300$ K companion. Our data provide 20 time-resolved spectra over an observation spanning 12.56 hours. We provide an empirical characterization for the spectra of both objects across time. For 2M1207 A, non-linear trend models are statistically favored within the ranges 0.6-2.3 $μ$m and 3.8-5.3 $μ$m. However, most of the periods constrained from sinusoidal models exceed the observing window, setting a lower limit of 12.56 hours. We find the data at H$α$ and beyond 4.35 $μ$m show a moderate time correlation, as well as a pair of light curves at 0.73-0.80 $μ$m and 3.36-3.38 $μ$m. For 2M1207 b, light curves integrated across 0.86-1.77 $μ$m and 3.29-4.34 $μ$m support linear trend models. Following the interpretation of Zhang et. al. (2025), we model the 2M1207 b data with two 1D atmospheric components, both with silicate and iron condensates. The model of time variability as changes to the cloud filling factor shows broad consistency with the variability amplitudes derived from our data. Our amplitudes, however, disagree with the models at $\approx$0.86-1 $μ$m. While an additional model component such as rainout chemistry may be considered here, our analysis is limited by a low signal-to-noise ratio. Our results demonstrate the capability of JWST to simultaneously monitor the spectral variability of a planetary-mass companion and host at low contrast.

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arXiv2025

Bioverse: Assessing the Ability of Direct Imaging Surveys to Empirically Constrain the Habitable Zone via Trends in Albedo

Will future direct imaging missions such as NASA's upcoming Habitable Worlds Observatory (HWO) be able to understand Earth-sized planets as a population? In this study, we simulate the ability of space-based coronagraphy missions to uncover trends in planetary albedo as a function of instellation, and potentially constrain the boundaries of the habitable zone. We adapt the Bioverse statistical comparative planetology framework to simulate the scientific output of possible designs for HWO. With this tool, we generate a synthetic planetary population with injected population-level trends in albedo and simulate the observability of planets. We then determine the statistical power to which these trends can be recovered as a function of the strength of the injected trend and the sample size of Earth-sized planets in the habitable zone (exoEarths). The strongest trends in albedo require a sample size of roughly 25-30 exoEarths to recover with high confidence. However, for weaker albedo trends, the required number of planets increases rapidly. If a mission is designed to meet the Decadal Survey's requirement of 25 exoEarths, it would be able to recover very strong trends in albedo associated with the habitable zone, but would struggle to confidently detect weaker trends. We explore multiple strategies to increase one's ability to recover weak trends, such as reducing the uncertainties in observables, incorporating additional observables such as planet colors, and obtaining direct constraints on planetary albedo from full spectral retrievals.

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arXiv2025

Wide Separation Planets In Time (WISPIT): Discovery of a Gap H$α$ Protoplanet WISPIT 2b with MagAO-X

Excellent (<25 mas) H$_α$ images of the star TYC 5709-354-1 led to the discovery of a rare H$_α$ protoplanet. This star was discovered by the WISPIT survey to have a large multi-ring transitional disk, and is hereafter WISPIT 2. Our H$_α$ images of 2025, April 13 and April 16 discovered an accreting (H$_α$ in emission) protoplanet: WISPIT 2b (r=309.43$\pm$1.56 mas; (~54 au deprojected), PA=242.21$\pm$0.41 degrees) likely clearing a dust-free gap between the two brightest dust rings in the transitional disk. Our SNR=12.5 detection gave an H$_α$ ASDI contrast of (6.5$\pm$0.5)x10$^{-4}$ and a H$_α$ line flux of (1.29$\pm$0.28)x10$^{-15}$ erg/s/cm$^2$. We also present L' photometry from LBT/LMIRcam of the planet (L'=15.30$\pm$0.05 mag) which, when coupled with an age of 5.1$^{+2.4}_{-1.3}$ Myr, yields a planet mass estimate of 5.3$\pm$1.0 Mjup from the DUSTY evolutionary models. WISPIT 2b is accreting at 2.25$^{-0.17}_{+3.75}$x10$^{-12}$ Msun/yr. WISPIT 2b is very similar to the other H$_α$ protoplanets in terms of mass, age, flux, and accretion rate. The inclination of the system (${\it i}$=44 degrees) is also, surprisingly, very similar to the other known H$α$ protoplanet systems which all cluster from 37$\leq{\it i}\leq$52 degrees. We argue this clustering has only a ~1.0% (2.6 sigma) probability of occurring randomly, and so we speculate that magnetospherical accretion might have a preferred inclination range (~37-52 degrees) for the direct (cloud free, low extinction) line of sight to the H-alpha line formation/shock region. We also find at 110mas (~15au deprojected) a close companion candidate (CC1) which may be consistent with an inner dusty 9$\pm$4 Mjup planet.

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arXiv2025

A Terminology and Quantitative Framework for Assessing the Habitability of Solar System and Extraterrestrial Worlds

The search for extraterrestrial life in the Solar System and beyond is a key science driver in astrobiology, planetary science, and astrophysics. A critical step is the identification and characterization of potential habitats, both to guide the search and to interpret its results. However, a well-accepted, self-consistent, flexible, and quantitative terminology and method of assessment of habitability are lacking. Our paper fills this gap based on a three year-long study by the NExSS Quantitative Habitability Science Working Group. We reviewed past studies of habitability, but find that the lack of a universally valid definition of life prohibits a universally applicable definition of habitability. A more nuanced approach is needed. We introduce a quantitative habitability assessment framework (QHF) that enables self-consistent, probabilistic assessment of the compatibility of two models: First, a habitat model, which describes the probability distributions of key conditions in the habitat. Second, a viability model, which describes the probability that a metabolism is viable given a set of environmental conditions. We provide an open-source implementation of this framework and four examples as a proof of concept: (a) Comparison of two exoplanets for observational target prioritization; (b) Interpretation of atmospheric O2 detection in two exoplanets; (c) Subsurface habitability of Mars; and (d) Ocean habitability in Europa. These examples demonstrate that our framework can self-consistently inform astrobiology research over a broad range of questions. The proposed framework is modular so that future work can expand the range and complexity of models available, both for habitats and for metabolisms.

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arXiv2025

Three Years of High-Contrast Imaging of the PDS 70 b and c Exoplanets at Hα with MagAO-X: Evidence of Strong Protoplanet Hα Variability and Circumplanetary Dust

We present 3 years of high-contrast imaging of the PDS 70 b and c accreting protoplanets with the new extreme AO system MagAO-X as part of the MaxProtoPlanetS survey of H$α$ protoplanets. In 2023 and 2024 our sharp (25-27 mas FWHM); well AO corrected (20-26% Strehl), deep (2-3.6hr) images detect compact (r~30 mas; r~3 au) circumplanetary disks (CPDs) surrounding both protoplanets. Starlight scattering off the dusty outer edges of these CPDs is the likely source of the bright compact continuum light detected within ~30 mas of both planets in our simultaneously obtained continuum 668 nm filter images. After subtraction of contaminating continuum and PSF residuals with pyKLIP ADI and SDI we obtained high-contrast ASDI H$α$ images of both planets in 2022, 2023 and 2024. We find the H$α$ line flux of planet b fell by (8.1$\pm$1.6)x10$^{-16}$ ergs/s/cm$^2$ a factor of 4.6 drop in flux from 2022 to 2023. In March 2024, planet b continued to be faint with just a slight 1.6x rise to an H$α$ line flux of (3.64$\pm$0.87)x10$^{-16}$ ergs/s/cm$^2$. For c we measure a significant increase of (2.74$\pm$0.51)x10$^{-16}$ ergs/s/cm$^2$ from 2023 to 2024 which is a factor of 2.3x increase. So both protoplanets have recently experienced significant H$α$ variability with ~1 yr sampling. In 2024, planet c is brighter than b: as c is brightening and b generally fading. We also tentatively detect one new point source "CC3" inside the inner disk (~49 mas; at PA~295 deg; 2024) with orbital motion roughly consistent with a ~5.6 au orbit.

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