arXiv subjects

Joshua E. Schlieder

Publications and source records attributed to Joshua E. Schlieder.

At least 19 recordsLinked to original sources

arXiv2026

Assessing the Impact of High-Resolution Imaging on Statistical Validation of TESS Planet Candidates

High-resolution imaging is widely used to constrain false-positive scenarios in exoplanet validation, but it is a finite follow-up resource that reaches only a subset of candidates, and its population-level impact on validation outcomes has not been quantified through controlled removal experiments. Using an automated pipeline built on TRICERATOPS, we compute the false-positive probability (FPP) of 443 TESS planet candidates. For the 264 planet candidates with high-resolution imaging observations, we compute FPP with and without the corresponding contrast curves, allowing us to quantify the impact of the additional data. We find that 72% of 68 contrast-curve bearing validated planets would fail validation without their adopted contrast curves. The fraction requiring imaging decreases with increasing planet size, from 100% below $1.7~R_\oplus$ to $33\%$ above $4~R_\oplus$: within our sample and TRICERATOPS-based analysis, the availability of high-resolution imaging directly limits the yield of small-planet validation and the supply of validated targets for atmospheric characterization. Our analysis statistically validates 64 new TESS planets with sizes spanning 0.94 to 7.83 $R_\oplus$ across hosts of spectral type M through F. Four of these are highly amenable to JWST observations based on the transmission and emission spectroscopy metrics, and each achieves validation only with its imaging constraint.

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arXiv2026

Nancy Grace Roman Space Telescope Wide Field Instrument: Bright Point Source Saturation Response and Persistence Properties from Thermal-Vacuum Testing

The Nancy Grace Roman Space Telescope's Wide Field Instrument (WFI) will observe hundreds of thousands of bright stars across its Core Community Surveys, particularly in the dense stellar fields of the Galactic Bulge Time Domain Survey (GBTDS). Sources brighter than ~17th magnitude will saturate WFI detector pixels in typical survey exposures, with the brightest stars deeply saturating large pixel regions and potentially producing persistence signals that may impact subsequent observations. Prior detector characterization did not explore the regime of deep point source saturation. To address this gap, we conducted a bright star saturation test during WFI's second Thermal Vacuum test campaign (TVAC2) at BAE Space & Mission Systems in Boulder, CO. Using the Stimulus of Ray Cones (SORC) telescope simulator, we projected nine in-focus point sources through the F146 filter onto two Sensor Chip Assemblies (SCAs), with fluxes tuned to approximate stellar magnitudes ranging from ~4 to ~18 in ~170 s exposures. We present analyses of the saturation response and persistence properties of these detectors. We find that the saturated region of a ~4 mag source grows to ~150 pixels in diameter after ~170 s of illumination, compared to ~15 pixels for a ~12 mag source. Pixels adjacent to the expanding saturation front exhibit pronounced non-linear behavior consistent with charge leakage from saturated neighbors. For persistence, we find that the median signal in the first post-illumination dark exposure is broadly consistent across source magnitudes spanning ~4 to ~17, and that persistence decays to detector background levels ($\lesssim$0.05 e$^{-}$ s$^{-1}$) within approximately 20 minutes, consistent with flat field persistence measurements from the same TVAC2 campaign. These pre-flight characterization results inform community understanding of WFI detector response to prepare for Roman science.

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arXiv2026

Foundations for Discovery: A Coordinated Fleet Approach to NASA Astrophysics

This white paper presents an analysis of Astro2020 science priorities and NASA's future astrophysics mission architecture, advocating for a coordinated fleet of \$1--2B missions, smaller than typical Flagship observatories, but strategically designed to complement them, i.e. a ``Next Generation Great Observatories" program. The study addresses opportunities in current mission planning, design, and implementation and proposes a strategic approach to maximize scientific return on investment while strengthening partnerships across NASA divisions, other government organizations, universities, and industry.

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arXiv2026

NASA's Pandora SmallSat Mission: Simulating the Impact of Stellar Photospheric Heterogeneity and Its Correction

Stellar photospheric heterogeneity is a dominant astrophysical systematic impacting exoplanet transmission spectroscopy. NASA's Pandora SmallSat Mission is designed to address this challenge through contemporaneous visible photometry and NIR spectroscopy of exoplanet host stars. Here we present an end-to-end simulation study quantifying Pandora's ability to infer stellar photospheric properties and correct stellar contamination using out-of-transit observations. We construct eight representative stellar activity scenarios and generate 160 simulated Pandora datasets, incorporating time-dependent stellar spectra, instrument response, and noise. Given accurate models, Bayesian retrievals of Pandora spectrophotometry recover photospheric temperatures with typical uncertainties of ${\approx}30$ K, with no significant bias. Models with two spectral components (i.e., quiescent photosphere and spots) are strongly favored in 95% of cases; one-component models are preferred when true spot filling factors fall below a detection threshold of ${\approx}0.3$%. We propagate the true and inferred stellar parameters to compute true, inferred, and residual contamination signals under physically motivated spot geometries. For simple spot distributions, contamination signals of $10^2{-}10^3$ ppm are reduced to ${\lesssim}10$ ppm, well below Pandora's expected transmission spectroscopy precision (30$-$100 ppm). For more complex spot distributions, geometric degeneracies limit deterministic corrections, leaving residual contamination at the $10^3$ ppm level that must be mitigated using additional constraints, such as spot-crossing events and joint stellar-planetary retrievals of transmission spectra. These results define regimes in which stellar contamination can be corrected from stellar observations alone and show how Pandora stellar observations can identify cases where additional information is required.

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arXiv2025

TOI-1438: A rare system with two short-period sub-Neptunes and a tentative long-period Jupiter-like planet orbiting a K0V star

We present the detection and characterisation of the TOI-1438 multi-planet system discovered by TESS. We collected a series of follow-up observations including high-spectral resolution observations with HARPS-N over a period of five years. Our modelling shows that the K0V star hosts two transiting sub-Neptunes with Rb = 3.04 +/- 0.19 RE, Rc = 2.75 +/- 0.14 RE, Mb = 9.4 +/- 1.8 ME, and Mc = 10.6 +/- 2.1 ME. The orbital periods of planets b and c are 5.1 and 9.4 days, respectively, corresponding to instellations of 145 +/- 10 and 65 +/- 4 FE. The bulk densities are 1.8 +/- 0.5 and 2.9 +/- 0.7 g cm-3, respectively, suggesting a volatile-rich interior composition. We computed a set of planet interior structure models. Planet b presents a high-metallicity envelope that can accommodate up to 2.5 % in H/He in mass, while planet c cannot have more than 0.2 % as H/He in mass. For any composition of the core considered (Fe-rock or ice-rock), both planets would require a volatile-rich envelope. In addition to the two planets, the radial velocity (RV) data clearly reveal a third signal, likely coming from a non-transiting planet, with an orbital period of 7.6 +1.6 -2.4 years and a radial velocity semi-amplitude of 35+3-5 m s-1. Our best fit model finds a minimum mass of 2.1 +/- 0.3 MJ and an eccentricity of 0.25+0.08-0.11. However, several RV activity indicators also show strong signals at similar periods, suggesting this signal might (partly) originate from stellar activity. More data over a longer period of time are needed to conclusively determine the nature of this signal. If it is confirmed as a triple-planet system, TOI-1438 would be one of the few detected systems to date characterised by an architecture with two small, short-period planets and one massive, long-period planet, where the inner and outer systems are separated by an orbital period ratio of the order of a few hundred.

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arXiv2025

The Pandora SmallSat: A Low-Cost, High Impact Mission to Study Exoplanets and Their Host Stars

The Pandora SmallSat is a NASA flight project aimed at studying the atmospheres of exoplanets -- planets orbiting stars outside our Solar System. Pandora will provide the first dataset of simultaneous, multiband (visible and NIR), long-baseline observations of exoplanets and their host stars. Pandora is an ambitious project that will fly a 0.44 m telescope in a small form factor. To achieve the scientific goals, the mission requires a departure from the traditional cost-schedule paradigm of half-meter-class observatories. Pandora achieves this by leveraging existing capabilities that necessitate minimal engineering development, disruptive and agile management, trusted partnerships with vendors, and strong support from the lead institutions. The Pandora team has developed a suite of high-fidelity parameterized simulation and modeling tools to estimate the performance of both imaging channels. This has enabled a unique bottom-up approach to deriving trades and system requirements. Pandora is a partnership between NASA and Lawrence Livermore National Laboratory. The project completed its Critical Design Review in October 2023 and is slated for launch into Sun-synchronous, low-Earth orbit in Fall 2025.

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arXiv2025

Probing the Outskirts of M Dwarf Planetary Systems with a Cycle 1 JWST NIRCam Coronagraphy Survey

The population of giant planets on wide orbits around low-mass M dwarf stars is poorly understood, but the unprecedented sensitivity of JWST NIRCam coronagraphic imaging now provides direct access to planets significantly less massive than Jupiter beyond 10 AU around the closest, youngest M dwarfs. We present the design, observations, and results of JWST GTO Program 1184, a Cycle 1 NIRCam coronagraphic imaging survey of 9 very nearby and young low-mass stars at 3-5 micron wavelengths. In the F356W and F444W filters, we achieve survey median 5-sigma contrasts deeper than 10-5 at a separation of 1", corresponding to 0.20 MJup in F444W and 1.30 MJup in F356W at planet-star separations of 10 AU. Our results include 3-5 micron debris disk detections and the identification of many extended and point-like sources in the final post-processed images. In particular, we have identified two marginal point source candidates having fluxes and color limits consistent with model predictions for young sub-Jupiter mass exoplanets. Under the assumption that neither candidate is confirmed, we place the first direct-imaging occurrence constraints on M dwarf wide-orbit (semimajor axes 10-100 AU), sub-Jupiter mass exoplanets (0.3-1 MJup). We find frequency limits of < 0.10 and < 0.16 objects per star with 1 and 3-sigma confidence, respectively. This survey brings to the forefront the unprecedented capabilities of JWST NIRCam coronagraphic imaging when targeting young, low-mass stars and acts as a precursor to broader surveys to place deep statistical constraints on wide-orbit, sub-Jupiter mass planets around M dwarfs.

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arXiv2025

TOI-6324b: An Earth-Mass Ultra-Short-Period Planet Transiting a Nearby M Dwarf

We report the confirmation of TOI-6324 b, an Earth-sized (1.059 $\pm$ 0.041 R$_\oplus$) ultra-short-period (USP) planet orbiting a nearby ($\sim$20 pc) M dwarf. Using the newly commissioned Keck Planet Finder (KPF) spectrograph, we have measured the mass of TOI-6324 b 1.17 $\pm$ 0.22 M$_\oplus$. Because of its extremely short orbit of just $\sim$6.7 hours, TOI-6324 b is intensely irradiated by its M dwarf host, and is expected to be stripped of any thick, H/He envelope. We were able to constrain its interior composition and found an iron core mass fraction (CMF = 27$\pm$37%) consistent with that of Earth ($\sim$33%) and other confirmed USPs. TOI-6324 b is the closest to Earth-sized USP confirmed to date. TOI-6324 b is a promising target for JWST phase curve and secondary eclipse observations (Emission Spectroscopy Metric = 25) which may reveal its surface mineralogy, day-night temperature contrast, and possible tidal deformation. From 7 sectors of TESS data, we report a tentative detection of the optical phase curve variation with an amplitude of 42$\pm$28 ppm.

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arXiv2025

Planet Masses, Radii, and Orbits from NASA's K2 Mission

We report the masses, sizes, and orbital properties of 86 planets orbiting 55 stars observed by NASA's K2 Mission with follow-up Doppler measurements by the HIRES spectrometer at the W. M. Keck Observatory and the Automated Planet Finder at Lick Observatory. Eighty-one of the planets were discovered from their transits in the K2 photometry, while five were found based on subsequent Doppler measurements of transiting planet host stars. The sizes of the transiting planets range from Earth-size to larger than Jupiter (1-3 REarth is typical), while the orbital periods range from less than a day to a few months. For 32 of the planets, the Doppler signal was detected with significance greater than 5-sigma (51 were detected with >3-sigma significance). An important characteristic of this catalog is the use of uniform analysis procedures to determine stellar and planetary properties. This includes the transit search and fitting procedures applied to the K2 photometry, the Doppler fitting techniques applied to the radial velocities, and the spectral modeling to determine bulk stellar parameters. Such a uniform treatment will make the catalog useful for statistical studies of the masses, densities, and system architectures of exoplanetary systems. This work also serves as a data release for all previously unpublished RVs and associated stellar activity indicators obtained by our team for these systems, along with derived stellar and planet parameters.

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arXiv2025

The transmission spectrum of the potentially rocky planet L 98-59 c

We present observations of the 1.35+/-0.07 Earth-radius planet L 98-59 c, collected using Wide Field Camera 3 on the Hubble Space Telescope. L 98-59 is a nearby (10.6 pc), bright (H=7.4 mag), M3V star that harbors three small, transiting planets. As one of the closest known transiting multi-planet systems, L 98-59 offers one of the best opportunities to probe and compare the atmospheres of rocky planets that formed in the same stellar environment. We measured the transmission spectrum of L 98-59 c and the extracted spectrum showed marginal evidence (2.1σ) for wavelength-dependent transit depth variations that could indicate the presence of an atmosphere. We forward-modeled possible atmospheric compositions of the planet based on the transmission spectrum. Although L 98-59 was previously thought to be a fairly quiet star, we have seen evidence for stellar activity, and therefore we assessed a scenario where the source of the signal originates with inhomogeneities on stellar surface. We also see a correlation between transits of L 98-59 c and L 98-59 b collected 12.5 hours apart, which is suggestive (but at <2σ confidence) of a contaminating component from the star impacting the exoplanet spectrum. While intriguing, our results are inconclusive and additional data is needed to verify any atmospheric signal. Fortunately, additional data has been collected from both HST and JWST. Should this result be confirmed with additional data, L 98-59 c would be the first planet smaller than two Earth-radii with a detected atmosphere.

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arXiv2024

Demographics of M Dwarf Binary Exoplanet Hosts Discovered by TESS

M dwarfs have become increasingly important in the detection of exoplanets and the study of Earth-sized planets and their habitability. However, 20-30% of M dwarfs have companions that can impact the formation and evolution of planetary systems. We use high-resolution imaging and Gaia astrometry to detect stellar companions around M dwarf exoplanet hosts discovered by TESS and determine the projected separation and estimated stellar masses for each system. We find 47 companions around 216 M dwarfs and a multiplicity rate of $19.4\pm2.7$% that is consistent with field M dwarfs. The binary projected separation distribution is shifted to larger separations, confirming the lack of close binaries hosting transiting exoplanets seen in previous studies. We correct the radii of planets with nearby companions and examine the properties of planets in M dwarf multi-star systems. We also note three multi-planet systems that occur in close binaries ($\lesssim 50$ au) where planet formation is expected to be suppressed.

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arXiv2024

OrCAS: Origins, Compositions, and Atmospheres of Sub-neptunes. I. Survey Definition

Sub-Neptunes - volatile-rich exoplanets smaller than Neptune - are intrinsically the most common type of planet known. However, the formation and nature of these objects, as well as the distinctions between sub-classes (if any), remain unclear. Two powerful tools to tease out the secrets of these worlds are measurements of (i) atmospheric composition and structure revealed by transit and/or eclipse spectroscopy, and (ii) mass, radius, and density revealed by transit photometry and Doppler spectroscopy. Here we present OrCAS, a survey to better elucidate the origins, compositions, and atmospheres of sub-Neptunes. This radial velocity survey uses a repeatable, quantifiable metric to select targets suitable for subsequent transmission spectroscopy and address key science themes about the atmospheric & internal compositions and architectures of these systems. Our survey targets 26 systems with transiting sub-Neptune planet candidates, with the overarching goal of increasing the sample of such planets suitable for subsequent atmospheric characterization. This paper lays out our survey's science goals, defines our target prioritization metric, and performs light-curve fits and statistical validation using existing TESS photometry and ground-based follow-up observations. Our survey serves to continue expanding the sample of small exoplanets with well-measured properties orbiting nearby bright stars, ensuring fruitful studies of these systems for many years to come.

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arXiv2024

Flaring Activity for Low-Mass Stars in the $β$ Pictoris Moving Group

Stellar flares from K and M dwarfs release panchromatic radiation characterized by a significantly higher brightness temperature ($\sim$9-20 kK) than the star. The increased frequency of magnetic activity on young low-mass stars results in the energy released during flaring events becoming a notable contributor to the radiation environment. This study focuses on the $β$ Pictoris moving group (24 $\pm$ 3 Myr) for the analysis of young, low-mass star flaring rates within the framework of larger flare studies. The calibration of long-term optical flare statistics is crucial to updating flare activity-age relations and the interpretation of exoplanet atmosphere observations. Using the $β$ Pictoris moving group, we develop a modular flare extraction pipeline sensitive to low-mass stellar flares in observations from the Transiting Exoplanet Survey Satellite. This pipeline is built to characterize flare properties of these stars such as total energy and cumulative flare rate. Consistent with previous studies, this sample (N=49) shows higher cumulative flare rates than early type and old field stars by at least an order of magnitude. Fitted flare frequency distributions for both early and late type M dwarfs show an average slope of $1.58 \pm 0.23$ with earlier stars flaring with lower or similar rates to late types. A typical member in this sample has daily ($\mathrm{\sim 1 \, d^{-1}}$ ) flares with TESS band energies of $10^{32} - 10^{33}$ ergs. The optical flare rates and energies for this group provide essential context into the co-evolution of host stars and associated planets.

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arXiv2024

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems II: A 1 to 20 Micron Spectrum of the Planetary-Mass Companion VHS 1256-1257 b

We present the highest fidelity spectrum to date of a planetary-mass object. VHS 1256 b is a $<$20 M$_\mathrm{Jup}$ widely separated ($\sim$8\arcsec, a = 150 au), young, planetary-mass companion that shares photometric colors and spectroscopic features with the directly imaged exoplanets HR 8799 c, d, and e. As an L-to-T transition object, VHS 1256 b exists along the region of the color-magnitude diagram where substellar atmospheres transition from cloudy to clear. We observed VHS 1256~b with \textit{JWST}'s NIRSpec IFU and MIRI MRS modes for coverage from 1 $μ$m to 20 $μ$m at resolutions of $\sim$1,000 - 3,700. Water, methane, carbon monoxide, carbon dioxide, sodium, and potassium are observed in several portions of the \textit{JWST} spectrum based on comparisons from template brown dwarf spectra, molecular opacities, and atmospheric models. The spectral shape of VHS 1256 b is influenced by disequilibrium chemistry and clouds. We directly detect silicate clouds, the first such detection reported for a planetary-mass companion.

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arXiv2024

The TESS-Keck Survey XX: 15 New TESS Planets and a Uniform RV Analysis of all Survey Targets

The Transiting Exoplanet Survey Satellite (TESS) has discovered hundreds of new worlds, with TESS planet candidates now outnumbering the total number of confirmed planets from $\textit{Kepler}$. Owing to differences in survey design, TESS continues to provide planets that are better suited for subsequent follow-up studies, including mass measurement through radial velocity (RV) observations, compared to Kepler targets. In this work, we present the TESS-Keck Survey's (TKS) Mass Catalog: a uniform analysis of all TKS RV survey data which has resulted in mass constraints for 126 planets and candidate signals. This includes 58 mass measurements that have reached $\geq5σ$ precision. We confirm or validate 32 new planets from the TESS mission either by significant mass measurement (15) or statistical validation (17), and we find no evidence of likely false positives among our entire sample. This work also serves as a data release for all previously unpublished TKS survey data, including 9,204 RV measurements and associated activity indicators over our three year survey. We took the opportunity to assess the performance of our survey, and found that we achieved many of our goals including measuring the mass of 38 small ($<4R_{\oplus}$) planets, nearly achieving the TESS mission's basic science requirement. In addition, we evaluated the performance of the Automated Planet Finder (APF) as survey support and observed meaningful constraints on system parameters due to its more uniform phase coverage. Finally, we compared our measured masses to those predicted by commonly used mass-radius relations and investigated evidence of systematic bias.

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arXiv2024

Validation of a Third Planet in the LHS 1678 System

The nearby LHS 1678 (TOI-696) system contains two confirmed planets and a wide-orbit, likely-brown-dwarf companion, which orbit an M2 dwarf with a unique evolutionary history. The host star occupies a narrow "gap" in the HR diagram lower main sequence, associated with the M dwarf fully convective boundary and long-term luminosity fluctuations. This system is one of only about a dozen M dwarf multi-planet systems to date that hosts an ultra-short period planet (USP). Here we validate and characterize a third planet in the LHS 1678 system using TESS Cycle 1 and 3 data and a new ensemble of ground-based light curves. LHS 1678 d is a 0.98 +/-0.07 Earth radii planet in a 4.97-day orbit, with an insolation flux of 9.1 +0.9/-0.8 Earth insolations. These properties place it near 4:3 mean motion resonance with LHS 1678 c and in company with LHS 1678 c in the Venus zone. LHS 1678 c and d are also twins in size and predicted mass, making them a powerful duo for comparative exoplanet studies. LHS 1678 d joins its siblings as another compelling candidate for atmospheric measurements with the JWST and mass measurements using high-precision radial velocity techniques. Additionally, USP LHS 1678 b breaks the "peas-in-a-pod" trend in this system, although additional planets could fill in the "pod" beyond its orbit. LHS 1678's unique combination of system properties and their relative rarity among the ubiquity of compact multi-planet systems around M dwarfs makes the system a valuable benchmark for testing theories of planet formation and evolution.

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arXiv2024

JWST/NIRCam Detection of the Fomalhaut C Debris Disk in Scattered Light

Observations of debris disks offer important insights into the formation and evolution of planetary systems. Though M dwarfs make up approximately 80% of nearby stars, very few M-dwarf debris disks have been studied in detail -- making it unclear how or if the information gleaned from studying debris disks around more massive stars extends to the more abundant M dwarf systems. We report the first scattered-light detection of the debris disk around the M4 star Fomalhaut C using JWST's Near Infrared Camera (NIRCam; 3.6$~μ$m and 4.4$~μ$m). This result adds to the prior sample of only four M-dwarf debris disks with detections in scattered light, and marks the latest spectral type and oldest star among them. The size and orientation of the disk in these data are generally consistent with the prior ALMA sub-mm detection. Though no companions are identified, these data provide strong constraints on their presence -- with sensitivity sufficient to recover sub-Saturn mass objects in the vicinity of the disk. This result illustrates the unique capability of JWST for uncovering elusive M-dwarf debris disks in scattered light, and lays the groundwork for deeper studies of such objects in the 2--5$~μ$m regime.

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arXiv2024

A Multiwavelength Survey of Nearby M dwarfs: Optical and Near-Ultraviolet Flares and Activity with Contemporaneous TESS, Kepler/K2, \textit{Swift}, and HST Observations

We present a comprehensive multiwavelength investigation into flares and activity in nearby M~dwarf stars. We leverage the most extensive contemporaneous dataset obtained through the Transiting Exoplanet Sky Survey (TESS), Kepler/K2, the Neil Gehrels Swift Observatory (\textit{Swift}), and the Hubble Space Telescope (HST), spanning the optical and near-ultraviolet (NUV) regimes. In total, we observed 213 NUV flares on 24 nearby M dwarfs, with $\sim$27\% of them having detected optical counterparts, and found that all optical flares had NUV counterparts. We explore NUV/optical energy fractionation in M dwarf flares. Our findings reveal a slight decrease in the ratio of optical to NUV energies with increasing NUV energies, a trend in agreement with prior investigations on G-K stars' flares at higher energies. Our analysis yields an average NUV fraction of flaring time for M0-M3 dwarfs of 2.1\%, while for M4-M6 dwarfs, it is 5\%. We present an empirical relationship between NUV and optical flare energies and compare to predictions from radiative-hydrodynamic and blackbody models. We conducted a comparison of the flare frequency distribution (FFDs) of NUV and optical flares, revealing the FFDs of both NUV and optical flares exhibit comparable slopes across all spectral subtypes. NUV flares on stars affect the atmospheric chemistry, the radiation environment, and the overall potential to sustain life on any exoplanets they host. We find that early and mid-M dwarfs (M0-M5) have the potential to generate NUV flares capable of initiating abiogenesis.

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