arXiv subjects

Elisabeth R. Newton

Publications and source records attributed to Elisabeth R. Newton.

At least 19 recordsLinked to original sources

arXiv2026

HWO Target Stars and Systems: Activity and Rotation Catalog (ARC) of Potential Target Stars for the Habitable Worlds Observatory

A major goal of the Habitable Worlds Observatory (HWO) is to precisely characterize exoplanets and their atmospheres. However, magnetic activity from an exoplanet's host star can complicate measurements of both the stellar and planetary properties, and stellar activity can be an important factor in our interpretation of the evolutionary history of an exoplanet. In this work, we assess the extent to which magnetic activity has been characterized for potential HWO target stars by collating archival measurements of relevant observables as published in a broad range of photometric and spectroscopic datasets. We describe our data collection strategy, provide an overview of currently known activity and rotation properties in the Activity and Rotation Catalog (ARC) for potential HWO target stars, and briefly review known relationships between stellar inclination, rotation, activity, and age. Overall, we find that stellar activity (S-index and R'HK) and rotation (v sin i and Prot) properties have been measured for at least 70% systems that are currently of high interest as potential HWO atmospheric characterization targets. However, stellar activity is temporal in nature, such that activity properties should be regularly monitored in order to remain up-to-date for informing future observations. In particular, we find that stellar activity cycles are measured for fewer than 20% of high interest potential HWO target stars. Measuring a star's activity cycle is critical for anticipating times when higher levels of magnetic activity may occur during planned HWO observations, which may interfere with measuring precise exoplanet atmospheric characteristics.

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arXiv2026

Wrinkles in Time. II. Stellar Age Trends in Kinematic Signatures from Transient Spiral Structure

Spiral arms in the disks of galaxies like the Milky Way can generate kinematic signatures, which appear as ridges or wrinkles in action space. Such signatures have proven difficult to disentangle using kinematic measures alone. In this study, we investigate how including stellar age as an additional dimension for analysis may provide a novel insight into the physical characteristics, timescales, and nature of the progenitors of such perturbations, where these novel insights could contribute to our understanding of the history of spiral arms in the Milky Way. We used a suite of tracer particle simulations that modeled a variety of prescriptions for spiral arms to characterize observable trends. The Lindblad resonances of nonwinding spirals produce signature overdensities, or wrinkles, in a kinematic space that is typically associated with older stellar populations (high radial action). We find that these wrinkles are preferentially populated with stars that were initially in nearly circular orbits, kinematics that is generally correlated with younger stellar ages. It follows that the stellar age distribution of wrinkle populations could serve to place constraints on the past passage of a transient spiral pattern in the solar neighborhood. For example, our simulations suggest that a physically motivated spiral pattern could significantly populate a wrinkle with zero-age stars in orbits typically occupied by stars much older than the Sun.

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arXiv2026

A Galactic Perspective on the (Unremarkable) Relative Refractory Depletion Observed in the Sun

Over the last two decades, the Sun has been observed to be depleted in refractory elements as a function of elemental condensation temperature (\tcond) relative to $\sim80\%$ of its counterparts. We assess the impact of Galactic chemical evolution (GCE) on refractory element--\tcond\ trends for 109,500 unique solar analogs from the GALAH, APOGEE, Gaia RVS, and \cite{bedell18} surveys. We find that a star's \feh\ and \alphafe\ are predictive of its \tcond\ slope (\rsq\ = $15 \pm 5\%$, $23 \pm 10\%$ respectively) while \teff\ and \logg\ contribute more weakly (\rsq\ = $9 \pm 5\%$, $13 \pm 16\%$). The Sun's abundance pattern resembles that of more metal-rich (0.1 dex) and $α$-depleted stars ($-0.02$ dex), suggesting a connection to broader GCE trends. To more accurately model stars' nucleosynthetic signatures, we apply the K-process model from \cite{Griffith24}, which casts each star's abundance pattern as a linear combination of core-collapse and Type Ia supernovae contributions. We find the Sun appears chemically ordinary in this framework, consistent with the intrinsic population scatter expected from stellar nucleosynthesis. We show that refractory element--\tcond\ trends arise because elements with higher \tcond\ have higher contributions from core-collapse supernovae. Refractory element depletion trends primarily reflect nucleosynthetic enrichment patterns shaped by GCE and local ISM inhomogeneities, with these processes accounting for $> 90\%$ of the observed variation within $2σ$. This work highlights how abundance diversity due to local and global chemical enrichment complicates the interpretation of population-scale planet-related chemical signatures in current datasets.

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arXiv2026

Thermal Eclipse Observation of the Young Hot Neptune AU Mic b with Spitzer

We present the observation of a secondary eclipse of the young hot Neptune, AU Mic b, in the infrared using the Spitzer Space Telescope. Using a primary transit from Spitzer to constrain the system parameters, we tentatively detect an eclipse centered at $BJD=2458740.848893^{+0.00010}_{-0.000099}$ with an observed depth of $171\pm{29}$ ppm given an uninformed prior. This corresponds to a dayside brightness temperature of $T=1031\pm{58}$ K, which exceeds the calculated equilibrium temperature of $606\pm{19}$ K. We explore some possible explanations for these results, including inefficient heat redistribution, gravitational contraction, stellar pulsations, instrument systematics and choice of eclipse depth prior, but find none of these to be likely explanations for the observed eclipse parameters. We also explore the impact of correlated noise in the systematic trends, and we find that splitting the systematics into low-pass (smoothing) and high-pass trends is required to reach an optimal minimization of the low-frequency systematics in the resulting detrended light curve. Future observations with JWST are needed to confirm our eclipse detection with Spitzer.

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arXiv2026

A young progenitor for the most common planetary systems in the Galaxy

The Galaxy's most common known planetary systems have several Earth-to-Neptune-size planets in compact orbits. At small orbital separations, larger planets are less common than their smaller counterparts by an order of magnitude. The young star V1298 Tau hosts one such compact planetary system, albeit with four planets that are uncommonly large (5 to 10 Earth radii). The planets form a chain of near-resonances that result in transit-timing variations of several hours. Here we present a multi-year campaign to characterize this system with transit-timing variations, a method insensitive to the intense magnetic activity of the star. Through targeted observations, we first resolved the previously unknown orbital period of the outermost planet. The full 9-year baseline from these and archival data then enabled robust determination of the masses and orbital parameters for all four planets. We find the planets have low, sub-Neptune masses and nearly circular orbits, implying a dynamically tranquil history. Their low masses and large radii indicate that the inner planets underwent a period of rapid cooling immediately after dispersal of the protoplanetary disk. Still, they are much less dense than mature planets of comparable size. We predict the planets will contract to 1.5-4.0 Earth radii and join the population of super-Earths and sub-Neptunes that nature produces in abundance.

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arXiv2025

FUMES IV: Optical and Far-ultraviolet Spectra of a Flare on the M Dwarf GJ 4334

On 2017-09-20 we observed GJ 4334, an M5V dwarf rotating with a period of 23.5 days, simultaneously with both the Space Telescope Imaging Spectrograph aboard Hubble (1160 -- 1710 Angstroms) and the Dual Imaging Spectrograph mounted on the 3.5m telescope at Apache Point Observatory (3750 -- 5050; 5800 -- 6950 Angstroms) as part of a larger survey of intermediately active M dwarfs. GJ 4334 flared during the observation, starting with a rise in the flux of optical chromospheric emission lines, followed by the rapid rise and decay of multiple far-ultraviolet emission lines formed in the transition region, followed by the slow decay of the optical lines. We find significant broadening and asymmetries in the optical emission lines that are potentially from bulk plasma motion, a post-flare elevated flux in both the optical and far-ultraviolet, and trends in the rise and decay timescales of the Balmer series such that higher-order lines rise earlier and decay faster than lower-order lines. The equivalent durations of the flare in individual lines range from 800 -- 3e4 seconds, mapping to flare energies of 1e28 -- 3e29 erg for each line. To contextualize GJ 4334's flare behavior we measure and compare its optical flare frequency distribution with TESS to EV Lacertae, a similar mass but faster rotating M dwarf, and find that GJ 4334 has an excess of large flares relative to the power-law established by the majority of its smaller flares. This dataset is a rare opportunity to characterize flares near a critical transition in stellar magnetic activity.

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arXiv2025

Requirements for Joint Orbital Characterization of Cold Giants and Habitable Worlds with Habitable Worlds Observatory

We determine optimal requirements for the joint detection of habitable-zone planets and cold giant planets with the Habitable Worlds Observatory (HWO). Analysis of 164 nearby stars shows that a coronagraph outer working angle (OWA) of 1440 milliarcseconds (mas) is necessary to achieve 80-90% visibility of cold giants. Approximately 40 precursor radial velocity measurements with 1 m/s precision are required to adequately constrain orbital parameters before HWO observations. We demonstrate that 6-8 astrometric measurements distributed across the mission timeline, compared to radial velocity constraints alone and to astrometry constraints alone, significantly improve orbital parameter precision, enabling direct determination of orbital inclination with uncertainties of 0.8-3 degrees. For habitable-zone planet characterization, 4-5 epochs provide moderate confidence, while high-confidence (95%) confirmation requires 8+ observations. These specifications are essential for the comprehensive characterization of planetary system architectures and understanding the potential habitability of terrestrial exoplanets.

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arXiv2025

A Statistical Method for Constraining the Capability of the Habitable Worlds Observatory to Understand Ozone Onset Time in Earth Analogs

The oxygenation of Earth's atmosphere 2.3 billion years ago, which on exoplanets is expected to be most detectable via the UV ozone feature at $\sim$0.25 $μ$m, is often regarded as a sign of the emergence of photosynthetic life. On exoplanets, we may similarly expect life to oxygenate the atmosphere, but with a characteristic distribution of emergence times. In this paper, we test our ability to recover various "true" emergence time distributions as a function of 1) stellar age uncertainty and 2) number of Earth analogs in the sample. The absolute uncertainties that we recover, for diverse underlying distributions, are mostly independent of the true underlying distribution parameters, and are more dependent on sample size than stellar age uncertainty. For a sample size of 30 Earth analogs, and an HWO architecture sensitive to ozone at 1% of the current atmospheric level on Earth, we find that no ozone detections across the entire sample would place a 10$σ$ limit on the mean time of ozone emergence, regardless of stellar age uncertainty.

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arXiv2025

Disentangling Metallicity Effects in Hot Jupiter Occurrence Across Galactic Birth Radius and Phase-Space Density

We explore how the correlation between host star metallicity and giant planets shapes hot Jupiter occurrence as a function of Galactic birth radius (\rbirth) and phase-space density in the Milky Way disk. Using the GALAH and APOGEE surveys and a galaxy from the NIHAO simulation suite, we inject hot Jupiters around stars based on metallicity power laws, reflecting the trend that giant planets preferentially form around metal-rich stars. For \rbirth\ $\geq 5$ kpc, hot Jupiter occurrence decreases with \rbirth\ by $\sim -0.1%$ per kpc; this is driven by the Galaxy's chemical evolution, where the inner regions of the disk are more metal-rich. Differences in GALAH occurrence rates versus APOGEE's and the simulation's at \rbirth\ $< 5$ kpc arise from survey selection effects. APOGEE and the NIHAO simulation have more high-$α$ sequence stars than GALAH, resulting in average differences in metallicity (0.2--0.4 dex), $α$-process element enrichment (0.2 dex), and vertical velocities (7--14 km/s) at each \rbirth\ bin. Additionally, we replicate the result of \cite{Winter20}, which showed that over 92% of hot Jupiters are associated with stars in phase-space overdensities, or "clustered environments." However, our findings suggest that this clustering effect is primarily driven by chemical and kinematic differences between low and high-$α$ sequence star properties. Our results support stellar characteristics, particularly metallicity, being the primary drivers of hot Jupiter formation, which serves as the "null hypothesis" for interpreting planet demographics. This underscores the need to disentangle planetary and stellar properties from Galactic-scale effects in future planet demographics studies.

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arXiv2025

Searching for helium escape and a low density atmosphere around the 120 Myr old sub-Neptune HIP94235b using CRIRES+

Atmospheric mass loss is thought to induce the bimodality in the small planet population as we observe it today. Observationally, active mass loss can be traced by excess absorption in spectral lines of lighter species, such as the hydrogen Ly-alpha line and the metastable helium triplet. We search for helium escape from the young (120Myr old) sub-Neptune HIP94235b. We obtained two transit observations of HIP94235b using the CRyogenic InfraRed Echelle Spectrograph (CRIRES+) on the Very Large Telescope (VLT). We find no evidence for escaping helium across both visits, allowing us to place a mass loss rate upper limit of 10^11 g/s, based on 1D Parker wind models. Additionally, we search for molecular spectral features in the planet's transmission spectrum, and cross-correlate our observations with high-resolution template spectra for H2O, the dominating molecule in the Y-band. We detect no significant absorption. We demonstrate that some atmosphere models at 10x solar metallicity would have been retrievable if present. Through the null detection of neutral hydrogen and helium escape, we conclude the atmosphere of HIP94235b likely lacks a large hydrogen-helium envelope. This is consistent with the expectation of small planet photoevaporation models, which suggest most planets lose their primordial hydrogen-helium envelopes within 100Myr of evolution.

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arXiv2025

Far-ultraviolet flares and variability of the young M dwarf AU Mic: a non-detection of planet c in transit at Lyman-alpha

Atmospheric escape's potential to shape the exoplanet population motivates detailed observations of systems actively undergoing escape. AU Mic is a young and active M dwarf hosting two close-in transiting sub- to Neptune-sized planets. Atmospheric escape was previously detected on the inner planet b, with radially-blown neutral hydrogen producing ~30% blue-shifted absorption in Lyman-alpha. We obtained one HST/STIS transit of the outer planet c, to search for the planet's escaping atmosphere in transmission at Lyman-alpha and compare with AU Mic b. We detected 6 short-duration flares in Si IV and C IV, of which only one corresponded to a Lyman-alpha flare. We identified longer-duration stellar variability at the tens of percent level for lines less sensitive to stellar activity, including O I, C II and Lyman-alpha, which inhibits detection of an exosphere. We do not report absorption associated with an exosphere containing neutral hydrogen or any metals detectable in the far-ultraviolet, and discuss the implications of the non-detection. This work highlights the importance of 1) careful consideration of stellar variability in atmospheric escape observations, and 2) the dual-influence of photoionization and stellar wind when interpreting and modeling atmospheric escape.

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arXiv2025

Short-Term Balmer Line Emission Variability in M Dwarfs

M Dwarfs make up the majority of stars, offering an avenue for discovering exoplanets due to their smaller sizes. However, their magnetic activity poses challenges for exoplanet detection, characterization, and planetary habitability. Understanding its magnetic activity, including surface starspots and internal dynamos, is crucial for exoplanet research. In this study, we present short-term variability in four Balmer emission lines \ha, \hb, \hg, and \hd\ for a sample of 77 M dwarfs of varying spectral types, and binarity. Stars were observed using the MDM Observatory's Ohio State Multi-Object Spectrograph on the 2.4m Telescope and the Modular Spectrograph on the 1.3 m Telescope. These data are combined with TESS photometry to explore the connection between spectroscopic and photometric variability. We observe sporadic short-term variability in Balmer lines for some stars, on timescale $\gtrsim$ 15-min, but much shorter than the stellar rotation period. We calculate periods for stars lacking those measurements, re-evaluated the relationship between amplitude (\rvar)-activity relation for the \ha \ line from \citet{garcia_soto_contemporaneous_2023}, and extended our analysis to the \hb, \hg \ and \hd \ lines, which indicates that the relation becomes increasingly dispersed for higher-order Balmer lines. This is consistent with increased intrinsic variability from lower to higher order lines. Additionally, we compute the Balmer decrement, using \hb \ as the fiducial, for stars where we could measure \hg \ and/or \hd. The Balmer decrement can show distinct patterns during white-light flares, with significant differences even for the same star. We also find evidence for dark spots on \object{TIC 283866910}.

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arXiv2024

A giant planet transiting a 3-Myr protostar with a misaligned disk

Astronomers have found more than a dozen planets transiting 10-40 million year old stars, but even younger transiting planets have remained elusive. A possible reason for the lack of such discoveries is that newly formed planets are not yet in a configuration that would be recognized as a transiting planet or cannot exhibit transits because our view is blocked by a protoplanetary disk. However, we now know that many outer disks are warped; provided the inner disk is depleted, transiting planets may thus be visible. Here we report the observations of the transiting planet IRAS 04125+2902 b orbiting a 3 Myr, 0.7 M$_\odot$, pre-main sequence star in the Taurus Molecular Cloud. IRAS 04125+2902 hosts a nearly face-on (i $\sim$ 30$^\circ$) transitional disk and a wide binary companion. The planet has a period of 8.83 days, a radius of 10.9 R$_\oplus$ (0.97R$_J$), and a 95%-confidence upper limit on its mass of 90M$_\oplus$ (0.3M$_J$) from radial velocity measurements, making it a possible precursor of the super-Earths and sub-Neptunes that are commonly found around main-sequence stars. The rotational broadening of the star and the orbit of the wide (4", 635 AU) companion are both consistent with edge-on orientations. Thus, all components of the system appear to be aligned except the outer disk; the origin of this misalignment is unclear. Given the rare set of circumstances required to detect a transiting planet at ages when the disk is still present, IRAS 04125+2902 b likely provides a unique window into sub-Neptunes immediately following formation.

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arXiv2024

The Featherweight Giant: Unraveling the Atmosphere of a 17 Myr Planet with JWST

The characterization of young planets (< 300 Myr) is pivotal for understanding planet formation and evolution. We present the 3-5$μ$m transmission spectrum of the 17 Myr, Jupiter-size ($R$ $\sim$10$R_{\oplus}$) planet, HIP 67522 b, observed with JWST/NIRSpec/G395H. To check for spot contamination, we obtain a simultaneous $g$-band transit with SOAR. The spectrum exhibits absorption features 30-50% deeper than the overall depth, far larger than expected from an equivalent mature planet, and suggests that HIP 67522 b's mass is $<$20 $M_{\oplus}$ irrespective of cloud cover and stellar contamination. A Bayesian retrieval analysis returns a mass constraint of $13.8\pm1.0M_{\oplus}$. This challenges the previous classification of HIP 67522 b as a hot Jupiter and instead, positions it as a precursor to the more common sub-Neptunes. With a density of $<$0.10g/cm$^{3}$, HIP 67522 b is one of the lowest density planets known. We find strong absorption from H$_{2}$O and CO$_{2}$ ($\ge7σ$), a modest detection of CO (3.5$σ$), and weak detections of H$_2$S and SO$_2$ ($\simeq2σ$). Comparisons with radiative-convective equilibrium models suggest supersolar atmospheric metallicities and solar-to-subsolar C/O ratios, with photochemistry further constraining the inferred atmospheric metallicity to 3$\times$10 Solar due to the amplitude of the SO$_2$ feature. These results point to the formation of HIP 67522 b beyond the water snowline, where its envelope was polluted by icy pebbles and planetesimals. The planet is likely experiencing substantial mass loss (0.01-0.03 M$_{\oplus}$ Myr$^{-1}$), sufficient for envelope destruction within a Gyr. This highlights the dramatic evolution occurring within the first 100 Myr of its existence.

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arXiv2024

TESS Investigation -- Demographics of Young Exoplanets (TI-DYE) II: a second giant planet in the 17-Myr system HIP 67522

The youngest ($<$50 Myr) planets are vital to understand planet formation and early evolution. The 17 Myr system HIP 67522 is already known to host a giant ($\simeq$10$R_\oplus$) planet on a tight orbit. In the discovery paper, Rizzuto et al. 2020 reported a tentative single transit detection of an additional planet in the system using TESS. Here, we report the discovery of HIP 67522 c which matches with that single transit event. We confirm the signal with ground-based multi-wavelength photometry from Sinistro and MuSCAT4. At a period of 14.33 days, planet c is close to a 2:1 mean motion resonance with b (6.96 days or 2.06:1). The light curve shows distortions during many of the transits, which are consistent with spot crossing events and/or flares. Fewer stellar activity events are seen in the transits of planet b, suggesting that planet c is crossing a more active latitude. Such distortions, combined with systematics in the TESS light curve extraction, likely explain why planet c was previously missed.

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arXiv2024

Searching for Neutral Hydrogen Escape from the 120 Myr Old Sub-Neptune HIP94235b using HST

HIP94235 b, a 120 Myr old sub-Neptune, provides us the unique opportunity to study mass loss at a pivotal stage of the system's evolution: the end of a 100 million year (Myr) old phase of intense XUV irradiation. We present two observations of HIP94235 b using the Hubble Space Telescope's Space Telescope Imaging Spectrograph (HST/STIS) in the Ly-alpha wavelength region. We do not observe discernible differences across either the blue and red wings of the Ly-alpha line profile in and out of transit, and report no significant detection of outflowing neutral hydrogen around the planet. We constrain the rate of neutral hydrogen escaping HIP94235 b to an upper limit of 10^13 g/s, which remains consistent with energy-limited model predictions of 10^11 g/s. The Ly-alpha non-detection is likely due to the extremely short photoionization timescale of the neutral hydrogen escaping the planet's atmosphere. This timescale, approximately 15 minutes, is significantly shorter than that of any other planets with STIS observations. Through energy-limited mass loss models, we anticipate that HIP94235 b will transition into a super-Earth within a timescale of 1 Gyr.

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arXiv2024

TESS Hunt for Young and Maturing Exoplanets (THYME) X: a two-planet system in the 210 Myr MELANGE-5 Association

Young (<500 Myr) planets are critical to studying how planets form and evolve. Among these young planetary systems, multi-planet configurations are particularly useful as they provide a means to control for variables within a system. Here, we report the discovery and characterization of a young planetary system, TOI-1224. We show that the planet-host resides within a young population we denote as MELANGE-5 . By employing a range of age-dating methods -- isochrone fitting, lithium abundance analysis, gyrochronology, and Gaia excess variability -- we estimate the age of MELANGE-5 to be 210$\pm$27 Myr. MELANGE-5 is situated in close proximity to previously identified younger (80 -110 Myr) associations, Crius 221 and Theia 424/Volans-Carina, motivating further work to map out the group boundaries. In addition to a planet candidate detected by the TESS pipeline and alerted as a TESS Object of Interest, TOI-1224 b, we identify a second planet, TOI-1224 c, using custom search tools optimized for young stars (Notch and LOCoR). We find the planets are 2.10$\pm$0.09$R_\oplus$ and 2.88$\pm$0.10$R_\oplus$ and orbit their host star every 4.18 and 17.95 days, respectively. With their bright ($K$=9.1 mag), small ($R_{*}$=0.44R$_{\odot}$), and cool ($T_{eff}$ =3326K) host star, these planets represent excellent candidates for atmospheric characterization with JWST.

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arXiv2024

An early giant planet instability recorded in asteroidal meteorites

Giant planet migration appears widespread among planetary systems in our Galaxy. However, the timescales of this process, which reflect the underlying dynamical mechanisms, are not well constrained, even within the solar system. Since planetary migration scatters smaller bodies onto intersecting orbits, it would have resulted in an epoch of enhanced bombardment in the solar system's asteroid belt. To accurately and precisely quantify the timescales of migration, we interrogate thermochronologic data from asteroidal meteorites, which record the thermal imprint of energetic collisions. We present a database of 40K-40Ar system ages from chondrite meteorites and evaluate it with an asteroid-scale thermal code coupled to a Markov chain Monte Carlo inversion. Simulations require bombardment in order to reproduce the observed age distribution and identify a bombardment event beginning 11.3 +9.5/-6.6 million years after the Sun formed (50% credible interval). Our results associate a giant planet instability in our solar system with the dissipation of the gaseous protoplanetary disk.

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