arXiv subjects

Emily K. Pass

Publications and source records attributed to Emily K. Pass.

10 recordsLinked to original sources

arXiv2026

Open Clusters as Laboratories for Cool Star Evolution: Highlights from the Cool Stars 23 Splinter Session

Open clusters remain among the most powerful laboratories for calibrating how fundamental stellar properties such as rotation, magnetic activity, surface chemistry, and internal structure evolve over the pre-main-sequence to main-sequence and post-main-sequence stellar lifetime. Because cluster members share a common age, galactic environment, and initial composition, they provide empirical anchors upon which age-dating techniques such as gyrochronology, activity-age relations, and chemical clocks are built. This paper summarizes the Cool Stars 23 splinter session - Open Clusters as Laboratories for Cool Star Evolution, held on 15 June 2026 in Tokyo, Japan. The session comprised one invited review, ten contributed talks, and ten poster pop-up presentations, organized around three themes: the evolution of rotation, magnetic activity, and chemical abundances (Li-depletion, [C/N], [Y/Mg], and neutron-capture elements). We close with a summary of the open questions identified in the panel discussion and the observational and theoretical work that new surveys (e.g. Gaia DR4, 4MOST, WEAVE) and missions (e.g. PLATO, Roman) will enable over the coming years. Together, these efforts will help assess the current state of the field and shape its future directions.

astro-ph.SR↗

arXiv2026

A Uniform Determination of the Bulk Metallicities and Alpha Enrichments of Confirmed Exoplanet Systems with TRES

We present a uniform spectroscopic characterization of 625 F, G, and K stars hosting 859 confirmed exoplanets using high-resolution archival optical spectra from the Tillinghast Reflector Echelle Spectrograph (TRES). We use the neural network spectral code uberMS, which combines spectra with broadband photometry to estimate precise and accurate stellar parameters. We determine stellar effective temperatures, surface gravities, radii, luminosities, projected rotational velocities, [Fe/H] abundances, and [$\alpha$/Fe] enrichments for most confirmed planet hosts observed by TRES. This uniform catalog can be used for a broad range of astrophysical studies, particularly to explore links between stellar [$\alpha$/Fe] and a suite of observed exoplanet properties. Combining our metallicity measurements with galactic kinematics, we identify 58 planet hosts that are likely members of the thick disk. We investigate the chemical environments of giant-planet formation by comparing the [$\alpha$/Fe] distributions of giant-planet host stars across different metallicity regimes. We find that subsolar metallicity giant-planet hosts are significantly enhanced in [$\alpha$/Fe] relative to Fe-rich giant-planet hosts and to the average Fe-poor field star, at high statistical significance. This suggests that enhanced $\alpha$-element abundances may partially compensate for low-Fe content and thus enable the formation of giant planets in metal-poor environments. We additionally compare the [$\alpha$/Fe] distributions of single- and multi-planet hosts and find modest evidence that $\alpha$-enhanced stars may preferentially host multi-planet systems. Finally, we recover previously observed trends between stellar metallicity and planetary eccentricity.

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arXiv2026

The JWST Search for Earth-Luna Analogs: Upper Limits on Exomoons and Refined Ephemerides for TOI 700 d and e

While no conclusive detections of exomoons have been reported to date, planet formation theories predict that Luna-analog satellites should be a common outcome of the collisional dynamics in early extrasolar systems. Such satellites have the potential to unlock new avenues to learn about exoplanet systems, speaking to topics of habitability, tidal heating, planet formation, late-stage growth, planetary compositions, and more. Here we describe the results of our JWST program to search for Luna-analog exomoons around the rocky, habitable-zone M-dwarf planets TOI 700 d and e. We refine the ephemerides of both worlds, providing an order-of-magnitude improvement in period precision and a factor of 2-3 improvement in planetary radii. We identify a strong correlated noise signal with a timescale of $16\pm4$ minutes and an amplitude of $46\pm4$ ppm; similar signals have been observed in previous JWST analyses of other stars and have been ascribed to stellar granulation. This noise source inflates our error by a factor of 4 relative to photon-noise expectations in 10-minute bins and limits our sensitivity to moons: we determine that our observations are sensitive mainly to moons larger than Ganymede on periods longer than 2 days (i.e., moons larger than our solar system's natural satellites). If this noise could be corrected, we would be sensitive to Luna-analog moons. Future work to address this noise source will thus be critical for detecting exomoons in stellar transits, as well as for all other science cases that hope to take advantage of JWST white-light curves in the photon-noise limit.

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arXiv2026

Radial and Rotational Velocities of a Volume-Complete Sample of M Dwarfs with Masses 0.1-0.3 Msun within 15 parsecs

We present the results from a five-year campaign to gather multi-epoch, high-resolution spectra of a volume-complete sample of 413 M dwarfs with masses 10-30% that of the Sun that lie within 15 parsecs. We report weighted mean systemic radial velocities (RV) and rotational broadening measurements ($v \sin i$) for our targets. Our typical relative RV uncertainties are less than $50$ m/s for the isolated, slowly rotating targets in our sample, and increase but remain less than 1 km/s for more rapidly rotating stars. The majority of the single stars in our sample ($71\pm3$%) have rotational broadening below our detection limit of 3.4 km/s. When combined with astrometric data, our radial velocities allow us to calculate galactic space motions, which we use to assign thin or thick disk membership. We determine that 81% and 8% of our sample are highly probable thin and highly probable thick disk members, respectively. We report seven new multi-lined multiple systems and identify six additional targets with velocity variations indicative of long-period binaries, of which three are new detections. Finally, we find no significant difference in the stellar multiplicity rates of the thin disk ($22\pm2$%) and thick disk ($21\pm8$%) populations in our sample, implying that mid-M dwarfs are not significantly losing their companions at these relative ages. Our survey more than triples the number of these fully-convective stars with complete astrometric data and uniformly derived, multi-epoch, high-resolution RVs and rotational broadening measurements.

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arXiv2025

The HD 60779 Planetary System: A Transiting Sub-Neptune on a 30-day Orbit and a More Massive Outer World

We present the discovery of the planetary system orbiting the bright (V = 7.2), nearby (35 pc), Sun-like star HD 60779, which has a mass of 1.050 +/- 0.044 solar masses and a radius of 1.129 +/- 0.013 solar radii. We report two TESS transits and a subsequent CHEOPS transit of HD 60779 b, a sub-Neptune with a radius of 3.250 (+0.100 / -0.098) Earth radii on a 29.986175 (+0.000030 / -0.000033) day orbit. Additionally, 286 HARPS-N radial velocity measurements reveal the mass of planet b (14.7 +1.1 / -1.0 Earth masses) and the presence of an outer planet, HD 60779 c, with an orbital period of 104.25 (+0.30 / -0.29) days and a minimum mass (m sin i) of 27.7 +/- 1.6 Earth masses. Both planets' orbits are consistent with being circular, suggesting that they have a dynamically quiet history. The data are not sufficient to determine whether planet c transits. HD 60779's uniquely high systemic radial velocity (129.75 +/- 0.12 km/s) allows its Lyman-alpha emission to avoid absorption by the interstellar medium, making it a prime candidate for probing atmospheric escape from HD 60779 b. HD 60779 is also the third-brightest host of a sub-Neptune with orbital period greater than 25 days and with both mass and radius measured, distinguishing it in terms of accessibility to spectroscopic characterization.

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arXiv2025

Metallicities from High-Resolution TRES Spectra with uberMS: Performance Benchmarks and Literature Comparison

As the field of exoplanetary astronomy has matured, demand has grown for precise stellar abundances to probe subtle correlations between stellar compositions and planetary demographics. However, drawing population-level conclusions from the disparate measurements in the literature is challenging, with various groups measuring metallicities using bespoke codes with differing line lists, radiative transfer models, and other assumptions. Homogeneous analyses are thus critical. Here we use the neural-net framework uberMS to measure iron abundances and alpha enrichments from high-resolution optical spectra observed by the Tillinghast Reflector Echelle Spectrograph (TRES), a key resource used for the follow-up of candidate exoplanet hosts. To contextualize these measurements and benchmark our method's performance, we compare to external constraints on metallicity using the Hyades cluster, wide binaries, and asteroids, to external constraints on $T_{\rm eff}$ and $\log g$ using stars with interferometric radii, and to the results of other abundance measurement methods using overlap samples with the APOGEE and SPOCS catalogs, as well as by applying the SPC method directly to TRES spectra. We find that TRES-uberMS provides reliable parameter estimates with errors of roughly 100 K in $T_{\rm eff}$, 0.09 dex in $\log g$, and 0.04 dex in [Fe/H] for many nearby dwarf stars, although [Fe/H] performance is poorer for mid-to-late K dwarfs, with the bias worsening with decreasing $T_{\rm eff}$. Performance is also worse for evolved stars. For [$\alpha$/Fe], our error may be as good as 0.03 dex for dwarfs based on external benchmarks, despite sizable and variable systematic differences when comparing with specific alpha-element abundances from other catalogs.

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arXiv2025

FORECASTOR -- II. Simulating Galaxy Surveys with the Cosmological Advanced Survey Telescope for Optical and UV Research

The Cosmological Advanced Survey Telescope for Optical and UV Research (CASTOR) is a planned flagship space telescope, covering the blue-optical and UV part of the spectrum. Here we introduce the CASTOR image simulator, a Python GalSim package-based script capable of generating mock CASTOR images from an input catalogue. We generate example images from the CASTOR Wide, Deep, and Ultra-Deep surveys using simulated light-cones from the Santa Cruz Semi-Analytic Model. We make predictions for the performance of these surveys by comparing galaxies that are extracted from each image using Source Extractor to the input catalogue. We find that the Wide, Deep, and Ultra-Deep surveys will be 75% complete for point sources down to ~27, 29 and 30 mag, respectively, in the UV, u, and g filters, with the UV-split and u-split filters reaching a shallower depth. With a large area of ~2200 deg$^2$, the Wide survey will detect hundreds of millions of galaxies out to z~4, mostly with $M_\ast \gtrsim 10^9 M_\odot$. The Ultra-Deep survey will probe to z~5, detecting galaxies with $M_\ast \gtrsim 10^7 M_\odot$. These galaxy samples will enable precision measurements of the distribution of star formation in the cosmic web, connecting the growth of stellar mass to the assembly of dark matter halos over two thirds of the history of the Universe, and other core goals of CASTOR's legacy surveys. These image simulations and the tools developed to generate them will be a vital planning tool to estimate CASTOR's performance and iterate the telescope and survey designs prior to launch.

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arXiv2024

The Mass Dependence of Hα Emission and Stellar Spindown for Fully Convective M Dwarfs

Fully convective M dwarfs typically remain rapidly rotating and magnetically active for billions of years, followed by an abrupt and mass-dependent transition to slow rotation and quiescence. A robust understanding of this process is complicated by difficulties in estimating M-dwarf ages and potential dependencies on other variables such as birth environment or metallicity. To isolate the effect of mass, we consider M dwarfs in wide binaries. We identify 67 widely separated, fully convective (0.08-0.35M$_\odot$) M-dwarf binary systems using Gaia and measure the H$α$ feature for each component. We classify the pairs into three categories: systems where both components are active, systems where both are inactive, and candidate transition systems, where one component is active and the other inactive. We gather higher-resolution spectra of the candidate transition systems to verify that their behavior does not result from an unresolved third component, yielding one new triple with surprising activity levels. Neglecting this triple, we find 22 active, 36 inactive, and 8 transition pairs. Our results are consistent with the epoch of spindown for these binaries being primarily determined by mass, with mild second-order effects; we place a 1$σ$ upper limit of 0.5Gyr or 25% on the dispersion in the mass-dependent spindown relation. Our findings suggest that the large dispersion in spindown epoch previously observed for field stars of a given mass may stem from differences in birth environment, in addition to modest intrinsic stochasticity. We also see evidence that the wide binary population is dispersed over time due to dynamical processing.

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arXiv2022

Constraints on the Spindown of Fully-Convective M Dwarfs Using Wide Field Binaries

M dwarfs remain active over longer timescales than their Sunlike counterparts, with potentially devastating implications for the atmospheres of their planets. However, the age at which fully-convective M dwarfs transition from active and rapidly rotating to quiescent and slowly rotating is poorly understood, as these stars remain rapidly rotating in the oldest clusters that are near enough for a large sample of low-mass M dwarfs to be studied. To constrain the spindown of these low-mass stars, we measure photometric rotation periods for field M dwarfs in wide binary systems, primarily using TESS and MEarth. Our analysis includes M-M pairs, which are coeval but of unknown age, as well as M dwarfs with white dwarf or Sunlike primaries, for which we can estimate ages using techniques like white dwarf cooling curves, gyrochronology, and lithium abundance. We find that the epoch of spindown is strongly dependent on mass. Fully-convective M dwarfs initially spin down slowly, with the population of 0.2--0.3M$_\odot$ rapid rotators evolving from $P_{\rm rot} < 2$ days at 600 Myr to $2 < P_{\rm rot} < 10$ days at 1--3 Gyr before rapidly spinning down to long rotation periods at older ages. However, we also identify some variability in the spindown of fully-convective M dwarfs, with a small number of stars having substantially spun down by 600 Myr. These observations are consistent with models of magnetic morphology-driven spindown, where angular momentum loss is initially inefficient until changes in the magnetic field allow spindown to progress rapidly.

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arXiv2019

Estimating dayside effective temperatures of hot Jupiters and associated uncertainties through Gaussian process regression

In this work, we outline a new method for estimating dayside effective temperatures of exoplanets and associated uncertainties using Gaussian process (GP) regression. By applying our method to simulated observations, we show that the GP method estimates uncertainty more robustly than other model-independent approaches. We find that unbiased estimates of effective temperatures can be made using as few as three broad-band measurements (white-light HST WFC3 and the two warm Spitzer IRAC channels), although we caution that estimates made using only IRAC can be significantly biased. We then apply our GP method to the twelve hot Jupiters in the literature whose secondary eclipse depths have been measured by WFC3 and IRAC channels 1 and 2: CoRoT-2 b; HAT-P-7 b; HD 189733 b; HD 209458 b; Kepler-13A b; TrES-3 b; WASP-4 b; WASP-12 b; WASP-18 b; WASP-33 b; WASP-43 b; and WASP-103 b. We present model-independent dayside effective temperatures for these planets, with uncertainty estimates that range from $\pm$66 K to $\pm$136 K.

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