arXiv subjects

Emma Nabbie

Publications and source records attributed to Emma Nabbie.

9 recordsLinked to original sources

arXiv2026

Transit Timing Variations in TESS: A Catalog from the First Five Years

We present the first catalog of transit timing variations (TTVs) in TESS systems with multiple TESS Objects of Interest (TOIs) using data from Sector 1 to Sector 69, spanning the first five years of mission operations. With an initial sample of 175 multi-TOI systems, we find significant TTVs in 20 systems, 13 of which had not been previously detected. Our results are generally consistent with the findings of previous Kepler TTV catalogs, with compact systems more likely to have detectable TTVs. However, the TTV systems in TESS exhibit a pile-up at the 2:1 orbital period resonance, in contrast to the pile-up near the 3:2 resonance from previous Kepler catalogs. This provides a tentative indicator that there may be different disk migration recipes that Kepler systems favor versus TESS systems. This catalog is a vital first step in determining which orbital resonances migrating planets tend to occupy at the end of formation, and aims to provide a list of high-impact targets for future in-depth follow up.

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arXiv2026

JWST unveils a high mean molecular weight atmosphere for mini-Neptune TOI-1130b: Evidence for formation beyond the water ice line

We present the combined JWST/NIRSpec G395H and NIRISS SOSS transmission spectrum of a warm mini-Neptune, TOI-1130b (3.66 R$_{\oplus}$, 19.8 M$_{\oplus}$, $T_{eq}\sim825$ K). It is part of a rare and unique multi-planet system TOI-1130, which hosts an inner mini-Neptune and an outer hot Jupiter locked in a 2:1 mean motion resonance. From the transmission spectrum of TOI-1130b we detect multiple molecules -- H$_2$O (7.5$\sigma$), CO$_2$ (3.3$\sigma$), and SO$_2$ (3.6$\sigma$), as well as a tentative detection of CH$_4$ ($\sim$2$\sigma$). We find a strong optical slope in the NIRISS/SOSS spectrum, which is consistent with TESS and CHEOPS transit depth measurements. From equilibrium chemistry retrievals we measure the atmospheric metallicity ($\log{Z/Z_{\odot}}=1.8^{+0.4}_{-0.3}$) and C/O ratio ($<$0.75 at 3$\sigma$ level confidence) and constrain the atmospheric mean molecular weight, $\mu$ = 5.5$^{+1.3}_{-0.8}$ amu. These constraints are consistent with self-consistent forward model grids. We detect no significant He I 1.083$\mu$m absorption signal and put a mass-loss rate upper limit of $10^{11}$g\s$^{-1}$. The volatile-rich high mean molecular weight atmosphere of TOI-1130b along with the `pebble-filtering' effect of the outer hot Jupiter supports the ex-situ formation scenario beyond the water ice line and subsequent migration, coherent with its present orbital architecture. A volatile-rich formation scenario could also potentially explain the location of TOI-1130b at the edge of the `radius cliff'. This result hints that the mini-Neptune population may not a homogeneous formation history; rather, volatile-rich ex-situ formation also contributes to its population.

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arXiv2026

The Orbital Eccentricity--Radius Distribution for Warm, Single Planets in TESS

We characterize the radius-dependent eccentricity distribution of 219 warm (P = 8--50 days) systems with only one transiting planetary candidate identified during Sectors 1-69 of the TESS mission. Using the ``photoeccentric effect'' in a hierarchical Bayesian framework, we first model the population using discrete planetary size bins (sub-Neptunes, sub-Saturns, and Jovians). We then develop a continuous mixture model with weights governed by a logistic sigmoid function of radius. We find that the warm-single population is best described by two components: a dominant low-eccentricity mode ( = 0.039-0.038+0.018) and a secondary dynamically excited mode ( = 0.466-0.068+0.067). The fraction of planets belonging to this high-eccentricity component increases strongly with planet radius, characterized by a transition at a break radius of R_br = 9.2-1.1+1.9 R_e. This trend places warm sub-Saturns predominantly on the same low-eccentricity track as sub-Neptunes. In contrast, warm Jovians (8--16 R_e) are frequently eccentric, with 65-12+13% of the population in the high eccentricity mode. Under the assumption of a two-component model, we see tentative evidence for a bimodal Jovian distribution at ~2.7 sigma. Finally, we identify a non-negligible tail of highly eccentric sub-Neptunes (1--4 R_e), which comprise 16.2-6.4+5.2% of the population, consistent with excitation by non-transiting external companions.

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arXiv2025

A high mutual inclination system around KOI-134 revealed by transit timing variations

Few planetary systems have measured mutual inclinations, and even less are found to be non-coplanar. Observing the gravitational interactions between exoplanets is an effective tool to detect non-transiting companions to transiting planets. Evidence of these interactions can manifest in the light curve through transit timing variations (TTVs) and transit duration variations (TDVs). Through analysis of Kepler photometry and joint TTV-TDV modeling, we confirm the detection of KOI-134 b, a transiting planet with mass and size similar to Jupiter on a period of ~67 days, and find that it exhibits high TTVs (~20-hr amplitude) and significant TDVs. We explain these signals with the presence of an innermost non-transiting planet in 2:1 resonance with KOI-134 b. KOI-134 c has a mass $M = 0.220^{+0.010}_{-0.011} M_\text{Jup}$ and a moderately-high mutual inclination with KOI-134 b of $i_\text{mut} = 15.4_{-2.5}^{+2.8}{^\circ}$. Moreover, the inclination variations of KOI-134 b are so large that the planet is predicted to stop transiting in about 100 years. This system architecture cannot be easily explained by any one formation mechanism, with other dynamical effects needed to excite the planets' mutual inclination while still preserving their resonance.

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arXiv2025

The Eccentricity Distribution of Warm Sub-Saturns in TESS

We present the eccentricity distribution of warm sub-Saturns (4-8 Re, 8-200 day periods) as derived from an analysis of transit light curves from NASA's Transiting Exoplanet Survey Satellite (TESS) mission. We use the "photoeccentric" effect to constrain the eccentricities of 76 planets, comprising 60 and 16 from single- and multi-transiting systems, respectively. We employ Hierarchical Bayesian Modelling to infer the eccentricity distribution of the population, testing both a Beta and Mixture Beta distribution. We identify a few highly eccentric (e ~ 0.7-0.8) warm sub-Saturns with eccentricities that appear too high to be explained by disk migration or planet-planet scattering alone, suggesting high-eccentricity migration may play a role in their formation. The majority of the population have a mean eccentricity of e = 0.103+0.047-0.045, consistent with both planet-disk and planet-planet interactions. Notably, we find that the highly eccentric sub-Saturns occur in single-transiting systems. This study presents the first evidence at the population level that the eccentricities of sub-Saturns may be sculpted by dynamical processes.

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arXiv2024

Surviving in the Hot Neptune Desert: The Discovery of the Ultra-Hot Neptune TOI-3261b

The recent discoveries of Neptune-sized ultra-short period planets (USPs) challenge existing planet formation theories. It is unclear whether these residents of the Hot Neptune Desert have similar origins to smaller, rocky USPs, or if this discrete population is evidence of a different formation pathway altogether. We report the discovery of TOI-3261b, an ultra-hot Neptune with an orbital period $P$ = 0.88 days. The host star is a $V = 13.2$ magnitude, slightly super-solar metallicity ([Fe/H] $\simeq$ 0.15), inactive K1.5 main sequence star at $d = 300$ pc. Using data from the Transiting Exoplanet Survey Satellite and the Las Cumbres Observatory Global Telescope, we find that TOI-3261b has a radius of $3.82_{-0.35}^{+0.42}$ $R_{\oplus}$. Moreover, radial velocities from ESPRESSO and HARPS reveal a mass of $30.3_{-2.4}^{+2.2}$ $M_{\oplus}$, more than twice the median mass of Neptune-sized planets on longer orbits. We investigate multiple mechanisms of mass loss that can reproduce the current-day properties of TOI-3261b, simulating the evolution of the planet via tidal stripping and photoevaporation. Thermal evolution models suggest that TOI-3261b should retain an envelope potentially enriched with volatiles constituting $\sim$5% of its total mass. This is the second highest envelope mass fraction among ultra-hot Neptunes discovered to date, making TOI-3261b an ideal candidate for atmospheric follow-up observations.

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arXiv2024

Gliese 12 b, A Temperate Earth-sized Planet at 12 Parsecs Discovered with TESS and CHEOPS

We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a bright ($V=12.6$ mag, $K=7.8$ mag) metal-poor M4V star only $12.162\pm0.005$ pc away from the Solar System with one of the lowest stellar activity levels known for an M-dwarf. A planet candidate was detected by TESS based on only 3 transits in sectors 42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory, as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of $12.76144\pm0.00006$ days and a radius of $1.0\pm{0.1}$ R$_\oplus$, resulting in an equilibrium temperature of $\sim$315K. Gliese 12 b has excellent future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the Galaxy.

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arXiv2023

TOI-5126: A hot super-Neptune and warm Neptune pair discovered by $\textit{TESS}$ and $\textit{CHEOPS}$

We present the confirmation of a hot super-Neptune with an exterior Neptune companion orbiting a bright (V = 10.1 mag) F-dwarf identified by the $\textit{Transiting Exoplanet Survey Satellite}$ ($\textit{TESS}$). The two planets, observed in sectors 45, 46 and 48 of the $\textit{TESS}$ extended mission, are $4.74^{+0.16}_{-0.14}$ $R_{\oplus}$ and $3.86^{+0.17}_{-0.16}$ $R_{\oplus}$ with $5.4588385^{+0.0000070}_{-0.0000072}$ d and $17.8999^{+0.0018}_{-0.0013}$ d orbital periods, respectively. We also obtained precise space based photometric follow-up of the system with ESAs $\textit{CHaracterising ExOplanets Satellite}$ ($\textit{CHEOPS}$) to constrain the radius and ephemeris of TOI-5126 b. TOI 5126 b is located in the "hot Neptune Desert" and is an ideal candidate for follow-up transmission spectroscopy due to its high predicted equilibrium temperature ($T_{eq} = 1442^{+46}_{-40}$ K) implying a cloud-free atmosphere. TOI-5126 c is a warm Neptune ($T_{eq}= 971^{+31}_{-27}$ K) also suitable for follow-up. Tentative transit timing variations (TTVs) have also been identified in analysis, suggesting the presence of at least one additional planet, however this signal may be caused by spot-crossing events, necessitating further precise photometric follow-up to confirm these signals.

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arXiv2023

Two mini-Neptunes Transiting the Adolescent K-star HIP 113103 Confirmed with TESS and CHEOPS

We report the discovery of two mini-Neptunes in near 2:1 resonance orbits ($P=7.610303$ d for HIP 113103 b and $P=14.245651$ d for HIP 113103 c) around the adolescent K-star HIP 113103 (TIC 121490076). The planet system was first identified from the TESS mission, and was confirmed via additional photometric and spectroscopic observations, including a $\sim$17.5 hour observation for the transits of both planets using ESA CHEOPS. We place $\leq4.5$ min and $\leq2.5$ min limits on the absence of transit timing variations over the three year photometric baseline, allowing further constraints on the orbital eccentricities of the system beyond that available from the photometric transit duration alone. With a planetary radius of $R_{p}=1.829^{+0.096}_{-0.067}\,R_{\oplus}$, HIP 113103 b resides within the radius gap, and this might provide invaluable information on the formation disparities between super-Earths and mini-Neptunes. Given the larger radius $R_{p}=2.40^{+0.10}_{-0.08}\,R_{\oplus}$ for HIP 113103 c, and close proximity of both planets to HIP 113103, it is likely that HIP 113103 b might have lost (or is still losing) its primordial atmosphere. We therefore present simulated atmospheric transmission spectra of both planets using JWST, HST, and Twinkle. It demonstrates a potential metallicity difference (due to differences in their evolution) would be a challenge to detect if the atmospheres are in chemical equilibrium. As one of the brightest multi sub-Neptune planet systems suitable for atmosphere follow up, HIP 113103 b and HIP 113103 c could provide insight on planetary evolution for the sub-Neptune K-star population.

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