arXiv subjects

Munazza K. Alam

Publications and source records attributed to Munazza K. Alam.

At least 19 recordsLinked to original sources

arXiv2026

A Comprehensive Analysis of the Panchromatic Transmission Spectrum of the Hot-Saturn WASP-96 b: Nondetection of Haze, Possible Sodium Limb Asymmetry, Stellar Characterization, and Formation History

We conduct a reanalysis of the JWST NIRISS/SOSS observation of the hot-Saturn WASP-96 b. Initial analysis of this data revealed an enhanced Rayleigh scattering slope at the blue end of the transmission spectrum, suggesting the presence of hazes at high altitudes. In this work, we report non-detection of this slope, confirming an atmosphere clear of high-altitude aerosols consistent with the pre-JWST results. Also contrary to the initial result, our results indicate the presence of gray cloud deck, although at relatively low altitudes/high pressures. We further combined the NIRISS/SOSS spectrum with VLT, HST, and Spitzer to produce a transmission spectrum from 0.35 $μ$m to 5 $μ$m. We constrain the mass fraction of multiple chemical species, including: H$_2$O$=-2.62^{+0.43}_{-0.42}$, K$=-5.76^{+1.05}_{-1.13}$, and Na$=-3.40^{+0.90}_{-0.92}$. C/O ratio and metallicity are tentatively constrained at substellar values (C/O$_{planet}=0.57^{+0.07}_{-0.12}$ and [Fe/H]$_{planet}=0.01^{+0.46}_{-0.52}$ compared to C/O$_{star}=0.92\pm0.25$ and [Fe/H]$_{star}=0.24\pm0.05$). Inputing these composition constraints to interior models, we constrain a core mass of $43^{+8}_{-15}$ M$_\oplus$. This, in addition to our inferred super-stellar refractory-to-oxygen ratio ($Δ\log_{10}(R/O)=1.48^{+0.57}_{-0.62}$) and substellar C/O ratio, suggests that the core of WASP-96 b likely formed outside of water iceline, underwent disk-driven migration, and accreted its atmosphere inside the carbon soot line. We find evidence of atmospheric leading-trailing terminator asymmetries in the broadened sodium absorption feature with a transit time offset of 50 seconds, while the water features appear symmetric. CH$_4$, CO, and CO$_2$ remain unconstrained due to spectral coverage limits. Upcoming JWST NIRSpec/G395H observations (ID 4082, PI: M. Radica) will be crucial for constraining these carbon-bearing species.

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arXiv2026

No Helium Detected in LHS 1140 b from Four JWST NIRISS/SOSS Transits

In the effort to determine which low-mass exoplanets have atmospheres, LHS 1140 b remains one of the most favorable targets. Its large size (5.6 $\rm M_{\oplus}$ and 1.7 $\rm R_{\oplus}$) and relatively long orbital period (24.7 days) imply an atmosphere may be likely, and notably, recent interior models favor either a hydrogen-dominated "mini-Neptune" or a "water world" over a true terrestrial planet. Another possibility is that it has a helium-rich atmosphere. This hypothesis is supported by recent ground-based observations that detected the metastable helium triplet during transit. These observations indicated there may be current helium escape from the planet's upper atmosphere, yet the signal was not detected during a subsequent observation, suggesting time-variable escape. Here we present four observations of LHS 1140 b with JWST NIRISS/SOSS, which covers the metastable helium triplet, obtained between 2023 and 2026. These observations span the epoch of the ground-based measurements, and although none were contemporaneous with the ground-based transits, all four are sensitive to helium absorption at the previously reported level. However, we detect no helium absorption in any visit. We reject the best-fit ground-based model at $>3σ$ in each visit, and find no clear trend in mass-loss with time. Our results suggest the reported ground-based detection may be spurious, although variability cannot be excluded if detectable helium absorption occurs in $\lesssim50\%$ of transits. The nature of LHS 1140 b thus remains a mystery until future transmission and emission analyses are complete.

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arXiv2026

Early Exploration of the Scientific Discovery Space for the Habitable Worlds Observatory

The Habitable Worlds Observatory (HWO) is a future NASA flagship mission concept identified by the Astro2020 Decadal Survey as the highest priority for large space missions. HWO should conduct "transformative astrophysics" and search for biosignatures in the atmospheres of approximately 25 potentially Earth-like planets. To further the early-stage development of HWO, NASA formed the Science, Technology, Architecture Review Team (START). In turn, START invited the scientific community to join working groups to explore the potential discovery space. In this paper, we present 70 science cases that resulted from this process. The cases address four scientific pillars: growth of galaxies (15 cases), evolution of the elements (13 cases), solar systems in context (32 cases), and living worlds (10 cases). Combined, they would address 27 of the 30 science questions and discovery areas identified by Astro2020. The 140 observing programs needed for the 70 investigations encompass a rich variety of spectroscopic (for 87% of science cases) and photometric (for 30%) observations extending from the UV to the NIR. Additionally, high-contrast and polarimetric capabilities would be needed for 34% and 27% of science cases, respectively. Access to UV wavelengths is critical: 83% of science cases need data at wavelengths <400 nm, and 26% extend to <100 nm. In the NIR, 26% of science cases need observations at wavelengths >=2000 nm. Pursuing the full portfolio of science would also necessitate precise astrometry for planet mass measurement, rapid response capabilities, a large instantaneous field of regard, non-sidereal tracking, saturation mitigation strategies, and high dynamic range.

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arXiv2026

Breaking the brightness barrier: JWST/NIRCam DHS spectroscopy for high-precision time-series observations

Many of the most scientifically compelling exoplanets orbit bright nearby stars that exceed the brightness limits of existing JWST spectroscopic observing modes. To address this limitation, a new NIRCam Short Wavelength Grism Time-Series mode has been developed by combining the Dispersed Hartmann Sensor (DHS) with a new on-board multistripe detector readout capability. The DHS disperses the incoming light through multiple pupil sub-apertures, reducing the incident flux and providing slitless spectroscopy between approximately 1.0 and 2.3 um. The multistripe readout mode further increases the accessible brightness range (K ~ 2.5 - 5.7 mag, depending on the spectral type of the object), with the previous limit being K ~ 5.7 mag at 1.5 um, by reading only the detector regions containing the DHS spectra, reducing the detector frame time with the standard RAPID readout mode from 10.74 s to 1.36 s over even less when using smaller substripe sizes. Together with the simultaneous long-wavelength grism observations, the new mode provides spectroscopic continuous coverage from approximately 1.0 to 5.0 um for targets as bright as K ~ 2.5 mag. We present the first results of on-orbit commissioning of this new observing mode with the final stage consisting of observations of a full transit of the exoplanet WASP-18b, which allowed us to demonstrate the feasibility of using NIRCam DHS for high-precision time-series observations. The commissioning presented in this paper marks the first deployment of the multistripe detector readout on JWST. Beyond NIRCam DHS, this new capability will be extended to other spectroscopic modes, including NIRISS SOSS and NIRSpec PRISM. Bright nearby stars host many of the highest-priority targets for exoplanet atmospheric characterization, making multistripe an important new capability for maximizing the scientific return of JWST.

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arXiv2026

Characterizing Transiting Exoplanet Atmospheres in the 2030s with the Hubble Space Telescope

The Hubble Space Telescope inaugurated the era of exoplanet atmospheric characterization. While the James Webb Space Telescope has largely taken up the mantle of infrared atmospheric characterization, Hubble's unique short-wavelength capabilities remain unmatched. Recent theoretical advances in exoplanet atmospheric science combined with new observing strategies, like those offered by WFC3-UVIS/G280, have opened science cases that only Hubble can address for the foreseeable future. In this white paper, we discuss these new windows into the atmospheres of other worlds, focusing on characterization of their hydrostatic lower atmosphere, and identify the critical capabilities necessary for future observations. We highlight three overall science cases that will depend on the continued short-wavelength capabilities of Hubble: measuring aerosol scattering slopes, characterizing metal absorption in ultra-hot Jupiters, and understanding stellar activity with Transit Light Source effect decontamination and flare monitoring. Throughout, we highlight useful synergies between HST and JWST. This article is a response to the call for white papers by the Space Telescope Science Institute on "Building a Roadmap for Hubble science into the 2030s."

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arXiv2026

The role of the Hubble Space Telescope in advancing our understanding of atmospheric escape in exoplanets

An important evolutionary pathway for planetary atmospheres is escape to space, which has been studied on Earth and Mars for several decades and more recently in exoplanets. A particularly important regime is the hydrodynamic escape, wherein atmospheric mass escapes the planet at high rates in a collisional fluid outflow. This process is used to partly explain the early evolution of rocky planets in and out of the Solar System, as well as key aspects of exoplanet demographics. Hydrodynamic escape is not occurring in the Solar System planets, so our only option for such observations is through exoplanets. The ultraviolet (UV) capabilities of the Hubble Space Telescope (HST) are fundamental to detect hydrodynamic escape and measure the resulting mass-loss rates for a range of planetary systems and to identify targets for surveys with the Habitable Worlds Observatory. We discuss here what kinds of observations and instrument modes are necessary to continue studying atmospheric escape in exoplanets for the next decade, as well as how to advance our understanding of planetary evolution and habitability.

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arXiv2026

JWST COMPASS Program: The 3--5$μ$m transmission spectrum of LTT 1445 A b

The search for an atmosphere on the closest rocky M dwarf planet, LTT 1445 A b, has been the subject of intense investigation from both the ground and space. Here, we present the first JWST transmission spectrum of LTT 1445 A b using a single visit spanning 3-5~$μ$m using NIRSpec/G395H. We conduct two independent reductions of the data using both the Eureka! and ExoTiC-JEDI pipelines. Overall, we measure the NRS1 transit depths to a median precision of $\sim23$~ppm in 41 spectroscopic channels with uniform widths of 30 pixels ($\sim$ 0.02 $μ$m), and the NRS2 transit depths to $\sim36$~ppm precision in 65 spectroscopic channels, also with uniform widths of 30 pixels. We rule out any statistically significant spectral features at this precision and place limits on atmospheric metallicity using a grid of chemical equilibrium models with grey opaque clouds. Using NIRSpec/G395H alone, we can place limits on the atmospheric metallicity of $\gtrsim350~\times$ Solar when the opaque pressure level is greater than 0.01~bars. We also conduct a combined analysis of JWST/NIRSpec and HST/WFC3 transmission data and find our atmospheric limits can be extended $\gtrsim500~\times$ Solar when considering both datasets. Future analyses both in transit and emission will uncover whether there are detectable atmospheric features.

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arXiv2026

High Tide or Riptide on the Cosmic Shoreline? A Water-Rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ~486b from JWST Observations

Planets orbiting M-dwarf stars are prime targets in the search for rocky exoplanet atmospheres. The small size of M dwarfs renders their planets exceptional targets for transmission spectroscopy, facilitating atmospheric characterization. However, it remains unknown whether their host stars' highly variable extreme-UV radiation environments allow atmospheres to persist. With JWST, we have begun to determine whether or not the most favorable rocky worlds orbiting M dwarfs have detectable atmospheres. Here, we present a 2.8-5.2 micron JWST NIRSpec/G395H transmission spectrum of the warm (700 K, 40.3x Earth's insolation) super-Earth GJ 486b (1.3 R$_{\oplus}$ and 3.0 M$_{\oplus}$). The measured spectrum from our two transits of GJ 486b deviates from a flat line at 2.2 - 3.3 $σ$, based on three independent reductions. Through a combination of forward and retrieval models, we determine that GJ 486b either has a water-rich atmosphere (with the most stringent constraint on the retrieved water abundance of H2O > 10% to 2$σ$) or the transmission spectrum is contaminated by water present in cool unocculted starspots. We also find that the measured stellar spectrum is best fit by a stellar model with cool starspots and hot faculae. While both retrieval scenarios provide equal quality fits ($χ^2_ν$ = 1.0) to our NIRSpec/G395H observations, shorter wavelength observations can break this degeneracy and reveal if GJ 486b sustains a water-rich atmosphere.

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arXiv2026

A Ground-Based Transit Observation of the Long-Period Extremely Low-Density Planet HIP 41378 f

We present a ground-based transit detection of HIP 41378 f, a long-period ($P = 542$ days), extremely low-density ($0.09 \pm 0.02$ g cm$^{-3}$) giant exoplanet in a dynamically complex system. Using photometry from Tierras, TRAPPIST-North, and multiple LCOGT sites, we constrain the transit center time to $T_{C,6} = 2460438.891 \pm 0.052$ BJD TDB. This marks only the second ground-based detection of HIP 41378 f, currently the longest-period and longest-duration transiting exoplanet observed from the ground. We use this new detection, along with a recently published transit time from Rossiter-McLaughlin observations, to update the TTV solution for HIP 41378 f. We predict the next two transits will occur at $T_{C,7} = 2460980.793^{+0.098}_{-0.129}$ BJD TDB (2025 November 1) and $T_{C,8} = 2461522.653^{+0.213}_{-0.238}$ BJD TDB (2027 April 27). Incorporating new TESS Sector 88 data, we also rule out the 101-day orbital period alias for HIP 41378 d, and find that the remaining viable solutions are centered on the 278, 371, and 1113-day aliases. The latter two imply dynamical configurations that challenge the canonical view of planet e as the dominant perturber of planet f. Our results suggest that HIP 41378 d may instead play the leading role in shaping the TTV of HIP 41378 f.

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arXiv2026

JWST COMPASS: NIRSpec/G395H Transmission Observations of the Sub-Neptune HD 15337 c

We present the 3-5 $μ$m transmission spectrum of HD 15337 c (TOI-402.02), a sub-Neptune (2.526 R$_{\oplus}$, 6.792 M$_{\oplus}$, T$_{\rm eq}$$\sim$656 K) around a K1V star observed as part of the JWST COMPASS program. We reduce these observations with two pipelines and find consistent transmission spectra. The resulting median precisions in 30 pixel spectroscopic bins for visit 1 are $\sim$40 ppm and $\sim$70 ppm and for visit 2 are $\sim$30 ppm and $\sim$54 ppm for NRS1 and NRS2, respectively. We attribute the differing precisions to the lack of adequate pre-transit baseline in visit 1 from an early transit arrival caused by previously undetected transit timing variations (TTVs), hinting at a potential exterior companion. Our median JWST timing precision is 10 seconds, revealing TTVs $>$20 minutes when combined with previous TESS and CHEOPS data, highlighting JWST's TTV measurement capabilities. The transmission spectrum of HD 15337 c is featureless and can best be described by a step function with an offset between the NRS1 and NRS2 detectors, likely caused by instrumental systematics. From thermochemical equilibrium retrievals we find that, to $>$3$σ$, the data can rule out atmospheres with metallicities $<$600 or $<$310 $\times$ solar, depending on the reduction, for opaque pressures greater than a few millibars. HD 15337 c joins other sub-Neptunes with similar masses, radii, and temperatures in possessing a featureless transmission spectrum indicative of high metallicity and/or high-altitude aerosols and adds support to recent studies showing that aerosol opacity reaches a maximum for planets with equilibrium temperatures of 500-700 K.

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arXiv2026

JWST COMPASS: A NIRSpec G395H Transmission Spectrum of Radius Valley-Dweller TOI-260 b

We present a JWST/NIRSpec G395H transmission spectrum of TOI-260 b, a $T_\mathrm{eq}\sim 490$ K, $R_\mathrm{p} = 1.76\,R_\oplus$ planet. The transmission spectrum is derived by combining two transit observations, collected as part of the JWST COMPASS program. We achieved the same median transit depth precision of 37 ppm in both visits, and a median precision of 26 ppm when combining the spectroscopic light curves from the two visits. Implementing a 30-pixel-wide ($R\sim 200$) spectroscopic binning scheme, we find that the transmission spectrum is mostly featureless, with a possible feature around 3.17 $μ$m. We assess the significance of any features in the transmission spectrum with a suite of non-parametric models, which confirm the presence of a potential feature in the NRS1 bandpass and an offset between the NRS1 and NRS2 detectors. To investigate the atmospheric composition of TOI-260 b, we run a series of PLATON retrievals. We do not detect any clear molecular signatures, but the combined data from the two visits are sufficient to constrain the atmospheric metallicity to greater than $200\times$ solar, assuming no opaque deck $\lesssim2.5$ mbar. We also investigate causes of the potential feature near 3.17 $μ$m; while we find some compatible gaseous species and cannot fully discard an astrophysical origin, we suspect a systematics origin due to the variance in strength and position of the feature. Overall, this look at TOI-260 b adds to the small sample of radius-valley planets, which already seem to show a diversity in their atmospheric compositions. Determining the true nature of these enigmatic planets will require a larger telescope time investment.

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arXiv2026

Charge Migration and Residual Non-Linearity in NIRSpec BOTS Observations

We investigate the effect of charge migration and residual non-linearity on the JWST/NIRSpec G395H NRS1 and NRS2 detectors using Bright Object Time Series (BOTS) observations of the ultra-hot Jupiter WASP-121b. These full-orbit phase curve observations were taken over 37.8 hours (1.57 days), and provide an excellent testbed of the non-linearity behavior of NRS1 and NRS2 over long timescales. For both detectors, our analysis demonstrates charge losses at the center of the spectral trace and charge excesses at the trace edges. We find that the NRS1 detector displays ~3x larger deviations from linearity compared to NRS2. Given the large transit (~1.5%) and eclipse (~0.5%) signals for WASP-121b, we also investigate variations in the distribution of charge throughout the time-series observation. Our results show that charge distribution varies at different planetary orbital phases for NRS1, which manifests as a change in the morphology and shape of the spectral trace over the course of the time-series. The effect of charge distribution on the trace shape is not evident for NRS2.

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arXiv2025

Analyzing Exoplanet Transits Observed with the WFC3/UVIS G280 Grism

Here we describe a Jupyter notebook demonstrating methods for the reduction and analysis of exoplanet transit observations taken with the WFC3/UVIS G280 grism. Released on Space Telescope's hst_notebooks GitHub repository, this notebook presents an example workflow for processing time-series observations taken with the G280 grism - from the calibrated flat-fielded spectra to transit light curves ready for fitting. The specific routines presented in the notebook are explained here, and are meant to highlight data reduction steps that users will typically apply to extract transit light curves. The steps include background subtraction, spatial and temporal cosmic ray correction, spectral trace fitting, spectral extraction, and light curve generation. The end products of the routines in the Jupyter notebook are the raw broadband and spectroscopic light curves, which can be ingested into publicly available light curve fitting tools to extract planetary transmission spectra.

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arXiv2025

Additional JWST/NIRSpec Transits of the Rocky M Dwarf Exoplanet GJ 1132 b Reveal a Featureless Spectrum

As an archetypal M-dwarf rocky exoplanet, GJ 1132 b has a varied history of atmospheric measurements. At 1.13 $\rm R_{\oplus}$, 1.66 $\rm M_{\oplus}$, and 580 K, it orbits a bright, slowly rotating M dwarf in a 1.6-day period, making it a prime target for characterization. In this study, we combine two JWST NIRSpec/G395H transits previously reported by May and MacDonald et al. 2023 with two new NIRSpec/G395M transits to constrain the presence of an atmosphere. This marks the first time the G395H and G395M modes have been combined for a single target, and we report no difference in the quality of data between the two modes. For rocky M-dwarf studies, G395H may still be preferred if stacking transits to utilize the high-resolution flux-calibrated stellar spectra and assess evolving stellar heterogeneity. GJ 1132 b's co-added transmission spectrum is best-fit with a flat line. A thin steam atmosphere is also consistent with the data, but this interpretation is driven almost entirely by the first transit, which suggests an increase in cool spot coverage-fraction derived from the flux-calibrated stellar spectra. This demonstrates the importance of always considering stellar heterogeneity evolution in multi-visit transits, and also the importance of a "leave-one-transit-out" approach in modeling efforts of co-added transits. We combine these results with MIRI/LRS emission data (Xue et al. 2024) to show that together, transmission and emission are consistent with only the thinnest of atmospheres. Given GJ 1132 b's age and distance from the star, a thin atmosphere is not likely stable. Therefore, the simplest explanation is that GJ 1132 b is indeed a bare rock.

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arXiv2025

JWST COMPASS: A NIRSpec G395H Transmission Spectrum of the Super-Earth GJ 357 b

We present JWST NIRSpec/G395H transmission spectroscopy observations of GJ 357 b, a warm ($T_{\mathrm{eq}} \approx 525$ K) super-Earth ($1.2\ \mathrm{R_{\oplus}} $, $1.84\ \mathrm{M_{\oplus}} $) orbiting a nearby M3-type star, with a median precision of 18 ppm and 27 ppm in NRS1 and NRS2, respectively. These precisions are obtained by binning the spectrum into 53 spectroscopic channels with a resolution of 60 pixels (around 0.02 $μ$m) each. Our analysis of the transmission spectrum reveals no detectable atmospheric spectral features. By comparing the observed spectrum with 1D forward models, we rule out atmospheres with mean molecular weights (MMW) lower than 8 g/mol to $3 σ$, as well as atmospheres with metallicities less than 300x solar. The lack of a low MMW primary atmosphere is consistent with a primordial H$_2$ rich atmosphere having escaped, given the planet's $\gtrsim5$ Gyr age, relatively low surface gravity (log g = 3.09), and its likely history of substantial incident extreme ultraviolet radiation. We conclude that GJ 357 b most likely possesses either a high-MMW secondary atmosphere, perhaps rich in oxidized gases like CO$_2$, or is a bare rock with no atmosphere. Upcoming scheduled JWST thermal emission observations could help distinguish between these scenarios by detecting signatures indicative of atmospheric heat redistribution or molecular absorption.

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arXiv2025

Exoplanet Atmospheric Escape Observations with the Habitable Worlds Observatory

The Decadal Survey on Astronomy and Astrophysics 2020 highlights the importance of advancing research focused on discovering and characterizing habitable worlds. In line with this priority, our goal is to investigate how planetary systems evolve through atmospheric escape and to develop methods for identifying potentially Earth-like planets. By leveraging the ultraviolet (UV) capabilities of the Habitable Worlds Observatory (HWO), we can use transit spectroscopy to observe atmospheric escape in exoplanets and explore the processes that shape their evolution, assess the ability of small planets to retain their atmospheres, and search for signs of Earth-like atmospheres. To achieve this, we support the development of a UV spectrograph with moderate- to high-resolution capabilities for point-source observations, coverage of key spectral features in the 100-300 nm range, and detectors that can register high count rates reliably. This article is an adaptation of a science case document developed for the Characterizing Exoplanets Steering Committee within HWO's Solar Systems in Context Working Group.

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arXiv2025

The HUSTLE Program: The UV to Near-IR Transmission Spectrum of the Hot Jupiter KELT-7b

The ultraviolet and optical wavelength ranges have proven to be a key addition to infrared observations of exoplanet atmospheres, as they offer unique insights into the properties of clouds and hazes and are sensitive to signatures of disequilibrium chemistry. Here we present the 0.2-0.8 $μ$m transmission spectrum of the Teq = 2000 K Jupiter KELT-7b, acquired with HST WFC3/UVIS G280 as part of the HUSTLE Treasury program. We combined this new spectrum with the previously published HST WFC3/IR G141 (1.1-1.7 $μ$m) spectrum and Spitzer photometric points at 3.6$μ$m and 4.5$μ$m, to reveal a generally featureless transmission spectrum between 0.2 and 1.7 $μ$m, with a slight downward slope towards bluer wavelengths, and a asymmetric water feature in the 1.1-1.7 $μ$m band. Retrieval models conclude that the 0.2 - 1.7$μ$m spectrum is primarily explained by a high H- abundance ($\sim 10^{-5}$), significantly above the equilibrium chemistry prediction ($\sim 10^{-12}$), suggesting disequilibrium in KELT-7b's upper atmosphere. Our retrievals also suggest the presence of bright inhomogeneities in the stellar surface, and tentative evidence of CO2 at the Spitzer wavelengths. We demonstrate that with the UV-optical coverage provided by WFC3 UVIS/G280, we are able to confirm the presence and constrain the abundance of H-, and obtain evidence for bright stellar inhomogeneities that would have been overlooked using infrared data alone. Observations redward of 1$μ$m with JWST should be able to further constrain the abundance of H-, as well as confirm the presence of CO2 inferred by the two Spitzer datapoints.

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arXiv2025

HST SHEL: Revealing Haze and Confirming Elevated Metallicity in the Warm Neptune HAT-P-26b

We present a new and extended transmission spectrum of the warm Neptune HAT-P-26b spanning wavelengths between 0.29 - 5.0 microns. This spectrum is derived from new HST STIS G430L observations from the PanCET program, a reanalysis of the previously published HST STIS G750L data, along with the previously published HST WFC3 IR G102 and G141 data, and the two Spitzer IRAC photometric points at 3.6 and 4.5 microns. We present this analysis as part of the Sculpting Hubble's Exoplanet Legacy (SHEL) program, where the goals are to analyze all HST archival observations of transiting exoplanets using a uniform and homogeneous reduction technique. With the new wavelength coverage, we identify a scattering slope that is weaker than Rayleigh scattering and is best-matched by models incorporating a haze-only scenario. Our retrieval analysis reveals an atmospheric metallicity of 15(+22/-8) x solar which suggests that HAT-P-26b may have formed further out in the protoplanetary disk, in a region rich in hydrogen and helium but with fewer heavy elements, and later migrated inward. This super-solar metallicity places HAT-P-26b below the mass-metallicity trend of the solar system. Looking ahead, recent observations from JWST NIRISS/SOSS and NIRSpec/G495H will provide critical, high-precision data that extend the spectral coverage into the infrared to further constrain the atmospheric composition and structure of HAT-P-26b. These observations have the potential to confirm or refine the metallicity and haze scenario presented here, offering unprecedented insights into the atmospheric properties of warm Neptunes and the processes governing their formation and migration histories.

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