arXiv subjects

Natasha Latouf

Publications and source records attributed to Natasha Latouf.

At least 19 recordsLinked to original sources

arXiv2026

Possible Observational Survey Strategies to Maximize Exoplanet Yields: A Report from the Survey Strategies Task Group in the Exoplanet Science Yields Working Group

We present a variety of possible observational sequences from planet detection to characterization (i.e., survey strategies) for the initial exoEarth detection and characterization survey phase of the Habitable Worlds Observatory. An array of survey strategies were collated by the HWO Exoplanet Survey Strategies Task Group; by investigating and comparing expected resultant exoEarth yields for multiple survey strategies, we can better understand the most efficient strategy to characterize multiple planets in unconventional ways. We present eight varied survey strategies, presented as steps of Detection, Photometry, Orbit Measurement, and/or Characterization, including discussion of possible shortcomings and benefits of each strategy. We present exoEarth yield calculations from the Altruistic Yield Optimizer (AYO) and the Exoplanet Open-Source Imaging Mission Simulator (EXOSIMS) for select strategies, with initial considerations of thermal emission and detector noise. Herein, a yield is the expectation value given the astrophysical assumptions of the number of planets that meet the observational criteria during the survey. We find that AYO and EXOSIMS find the highest yields for H2O at 0.9 microns, although the calculated yields vary. When allowing for wavelength optimization within AYO, we find that H2O is most optimal to observe at 0.9 microns when given the full range of VIS and NIR values, with an expected exoEarth yield of 29.1. H2O and O2 dual characterization is possible at the expense of yield planet loss, with a calculated possible yield of 20.9 in the VIS. The characterization of CH4 and CO2 in the NIR result in the lowest exoEarth yields at 19.9 and 6.4 possible expected planets, respectively. Future work updating AYO and EXOSIMS is necessary to explore further survey strategies that follow different observation procedures, some of which is currently underway.

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arXiv2026

Ad Astra White Paper: A Pitch for the Next 25 Years of NASA's Physics of the Cosmos Program

Astrophysical observations of our universe have been key to our understanding of how the universe works. Shortly after the turn of the millennium, the National Research Council delivered \textit{Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century}. In the subsequent quarter-century, we have made substantial progress in answering each question. These advancements have, in part, arisen because of the success of major US facilities across several domains of physics, guided by long-term planning documents which still largely focus on these questions. This report seeks to provide a status update on each question, and to outline what space-based facilities are crucial for future progress, intended to guide NASA's preparatory work for the Astro2030 Decadal.

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arXiv2026

Wavelength Requirements for Life Detection via Reflected Light Spectroscopy of Rocky Exoplanets

Searching for signs of life is a primary goal of the Habitable Worlds Observatory (HWO). However, merely detecting oxygen, methane, or other widely discussed biosignatures is insufficient evidence for a biosphere. In parallel with biosignature detection, exoplanet life detection additionally requires characterization of the broader physicochemical context to evaluate planetary habitability and the plausibility that life could produce a particular biosignature in a given environment. Life detection further requires that we can confidently rule out photochemical or geological phenomena that can mimic life. Evaluating false-positive scenarios may require different observatory specifications than biosignature detection surveys. Here, we explore the coronagraph requirements for assessing habitability and for excluding known false-positive (and false-negative) scenarios for oxygen and methane. We find that broad wavelength coverage ranging from the near ultraviolet (0.26 $μ$m) and extending into the near infrared (1.7 $μ$m) is necessary to contextualize these potential biosignatures with HWO. The short-wavelength cutoff is driven by the need to identify Proterozoic-like biospheres via O$_3$, whereas the long-wavelength cutoff is driven by the need to contextualize O$_2$ and CH$_4$ biosignatures via constraints on carbon-bearing atmospheric species. The ability to obtain spectra with signal-to-noise ratios of 20-40 across this 0.26-1.7 $μ$m range (R=7 UV, R=140 VIS, and R=70 NIR) is also required. While not every Earth-analog biosignature and false positive can be unambiguously identified with these capabilities-and the plausibility and contextual clues of many biosignature false positives remain an area of active research-our minimal spectral recommendations would enable a broad search for Earth-like life assuming such observations are achievable for a meaningful number of HWO targets.

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arXiv2026

Modeling the Impact of Starspot Inhomogeneity on Spectroscopic Retrievals of Directly-Imaged Planets

Stellar activity is a major complication in the detection and characterization of exoplanets by both radial velocities and transits, and the upcoming Habitable Worlds Observatory (HWO) invites us to also consider its effect on direct imaging. Spectra of directly-imaged planets can vary with the activity of their host stars because the face of the star we see is not the same as the face reflected by the planet. This discrepancy could potentially result in inaccurate measurements of the planet's radius and unexpected, externally-caused variability in its contrast spectrum with the star. To assess the scientific capabilities and requirements of HWO, it is important that the magnitude of these effects be quantified. We present results of model retrievals of Earth-like exoplanets observed with an HWO-style survey, as they would appear when affected by starspots, using the ExoVista code for spectrum generation and the BARBIE code for spectroscopic retrieval. Both Solar-type stellar activity and highly active rapid rotators are considered and compared with an idealized quiescent host star. In the quiescent case, ${\rm SNR}\approx5$ is needed to detect atmospheric water vapor at 0.9 microns and ${\rm SNR}\approx13$ at 0.74 microns. We find that for Solar-type activity, the effect on retrievals will be negligible, but it could present problems for certain highly-active stars at limiting geometries. For an extreme case with a single large spot with 10\% coverage not visible to the observer, the SNR required for water detection increases to ${\rm SNR}\approx8$ at 0.9 microns and ${\rm SNR}\approx18$ at 0.74 microns. It also decreases the accuracy of the retrieved albedo, resulting in a value $\sim2/3$ of the true value. In light of these results, we estimate the impact that stellar variability and starspots may have on an HWO-style survey.

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arXiv2026

Understanding HWO's Field of Regard and Characterization Requirement Trade Space with a Dynamic Observation Scheduling Algorithm

The Habitable Worlds Observatory (HWO) aims to image and characterize at least 25 ExoEarth candidates (EECs). Achieving this goal requires a detailed understanding of the observatory's design trade space, including the operational efficiency of the EEC survey. This study quantifies the impact of two critical parameters: the instantaneous field of regard (FoR) and the number of characterization observations required per EEC ($N_\text{char}$). We introduce a novel dynamic scheduling algorithm implemented within the EXOSIMS framework that models information gain during the mission. The scheduler models the orbital information known about each planet and forecasts detection probabilities to make scheduling decisions. We explore a multi-dimensional trade space, varying aperture size (6.5 m and 8.0 m), dedicated EEC survey time (2.5, 5.0, 7.5 years), $N_\text{char}$ (1 to 4), and FoR ($15^\circ$ to $135^\circ$). Our results demonstrate that the FoR is a major driver of the mission yield, with the yield decreasing significantly when the FoR is less than $90^\circ$. We find that increasing $N_\text{char}$ imposes a significant cost to mission yield, as each additional characterization required reduces yield by approximately 22%. The cumulative impact of requiring four characterizations instead of one lowers the yield by approximately 52%. This harsh penalty can be partially mitigated by increasing the survey duration. The relative yield loss when increasing $N_\text{char}$ from 1 to 2 is 38% for a 2.5 year survey and 14% for a 7.5 year survey. Our results highlight the complex interactions between HWO's engineering constraints and science requirements, and emphasize that the EEC survey efficiency is a critical component of HWO's design space.

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arXiv2026

Bayesian Analysis for Remote Biosignature Identification on exoEarths (BARBIE) IV: Analyzing CO2 Detections in the Near-IR to Determine the Long-Wavelength Cut-off for the Habitable Worlds Observatory Coronagraph

We present our analysis of how the detectability of carbon dioxide (CO2) on an Earth-like planet varies with respect to signal-to-noise ratio (SNR), wavelength, and molecular abundance. Using the Bayesian Analysis for Remote Biosignature Identification on exoEarths (BARBIE) methodology, we can inform the optimal long-wavelength cut-off for the future Habitable Worlds Observatory (HWO) coronagraph. We test 25 evenly-spaced 20% bandpasses between 0.8-2.0μm, and simulate data spanning a range of SNRs and molecular abundance to analyze the relationship between wavelength and detectability for different planetary archetypes. We examine abundance levels from varying Earth epochs and a Venus-like archetype to investigate how detectability would change throughout the evolution of a rocky planet. Here, we present our results on the planetary conditions and technological requirements to strongly detect CO2. In addition, we analyze the degeneracy of CO2 with carbon monoxide (CO), methane (CH4), and water (H2O). We determine that any abundance of CO does not achieve strong detections and that CH4 and H2O play a pivotal role in the ability to detect CO2. We conclude that the optimal long-wavelength cut-off for the Habitable Worlds Observatory coronagraph should be 1.68μm.

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arXiv2026

Habitable Worlds Observatory (HWO): Living Worlds Community Working Group: The Search for Life on Potentially Habitable Exoplanets

The discovery of a biosphere on another planet would transform how we view ourselves, and our planet Earth, in relation to the rest of the cosmos. We now know Earth is one planet among eight circling our sun; our sun is part of a swirling galaxy of over one hundred billion other suns; and our galaxy is one of untold billions in the universe. While we do not yet know how many, if any, other biospheres exist on the countless worlds orbiting countless other suns, we stand at the precipice of a new era of discovery, enabled by powerful new facilities able to peer across the light years into the atmospheres of planets similar to our own. This article is an adaptation of a science case document (SCDD) developed for the NASA Astrophysics Flagship mission the Habitable Worlds Observatory (HWO) Science, Technology, and Architecture Review Team (START) Living Worlds Community Working Group.

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arXiv2025

Determining the Detectability of H2O with Photometric Observations using Bayesian Analysis for Remote Biosignature Identification on exoEarths (BARBIE)

We examine the detectability of water (H2O) in the reflected-light spectrum of an Earth-like exoplanet assuming a photometric observational approach rather than spectroscopic. By quantifying the detectability as a function of normalized exposure time, resolving power (R), and amount of spectral points, we can constrain whether spectroscopy or photometry is the more efficient observing procedure to detect H2O at varying abundances by measuring the broad 0.94 microns absorption feature using the Habitable Worlds Observatory (HWO). We simulate low-resolution spectroscopy (R = 10, 20, 30, presented as photometric bandwidth fraction 10%, 5%, 3% herein) as a proxy for narrow-band photometric observations, and constrain the wavelength range from 0.85 - 1.05 microns, to narrow focus on the 0.9 microns feature. We then constrain the number of spectral points to 2 or 3 points at each bandwidth fraction to investigate the impact of spectral point placement on detectability. Additionally, we take the signal-to-noise ratios (SNRs) for strong H2O detection and calculate the resultant exoplanet yields assuming photometric observation and compare to the yields from higher-resolution spectroscopic observations under different noise instances, characterization wavelength, noise floors, and aperture sizes. We find that H2O is strongly detectable at all bandwidth fractions depending on the spectral point placement, requiring a minimum of 3 spectral points, at a variety of normalized exposure time depending on the abundance of H2O. We also find that the detector noise is the main driver in determining whether photometry or spectroscopy results in higher yields. Photometry is the preferred observational method in high-noise cases, while spectroscopy is preferred in low-noise scenarios.

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arXiv2025

Paths to Robust Exoplanet Science Yield Margin for the Habitable Worlds Observatory

The Habitable Worlds Observatory (HWO) will seek to detect and characterize potentially Earth-like planets around other stars. To ensure that the mission achieves the Astro2020 Decadal's recommended goal of 25 exoEarth candidates (EECs), we must take into account the probabilistic nature of exoplanet detections and provide "science margin" to budget for astrophysical uncertainties with a reasonable level of confidence. In this study, we explore the probabilistic distributions of yields to be expected from a blind exoEarth survey conducted by such a mission. We identify and estimate the impact of all major known sources of astrophysical uncertainty on the exoEarth candidate yield. As expected, eta_Earth uncertainties dominate the uncertainty in EEC yield, but we show that sampling uncertainties inherent to a blind survey are another important source of uncertainty that should be budgeted for during mission design. We adopt the Large UV/Optical/IR Surveyor Design B (LUVOIR-B) as a baseline and modify the telescope diameter to estimate the science margin provided by a larger telescope. We then depart from the LUVOIR-B baseline design and identify six possible design changes that, when compiled, provide large gains in exoEarth candidate yield and more than an order of magnitude reduction in exposure times for the highest priority targets. We conclude that a combination of telescope diameter increase and design improvements could provide robust exoplanet science margins for HWO.

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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

Bayesian Analysis for Remote Biosignature Identification on exoEarths (BARBIE) \RNum{3}: Introducing the KEN

We deploy a newly-generated set of geometric albedo spectral grids to examine the detectability of methane (CH4) in the reflected-light spectrum of an Earth-like exoplanet at visible and near-infrared wavelengths with a future exoplanet imaging mission. By quantifying the detectability as a function of signal-to-noise ratio (SNR) and molecular abundance, we can constrain the best methods of detection with the high-contrast space-based coronagraphy slated for the next generation telescopes such as the Habitable Worlds Observatory (HWO). We used 25 bandpasses between 0.8 and 1.5 microns. The abundances range from a modern-Earth level to an Archean-Earth level, driven by abundances found in available literature. We constrain the optimal 20%, 30%, and 40% bandpasses based on the effective SNR of the data, and investigate the impact of spectral confusion between CH4 and H2O on the detectability of each one. We find that a modern-Earth level of CH4 is not detectable, while an Archean Earth level of CH4 would be detectable at all SNRs and bandpass widths. Crucially, we find that CH4 detectability is inversely correlated with H2o abundance, with required SNR increasing as H2O abundance increases, while H2O detectability depends on CH4 abundance and selected observational wavelength, implying that science requirements for the characterization of Earth-like planet atmospheres in the VIS/NIR should consider the abundances of both species in tandem.

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arXiv2024

The pale blue dot: using the Planetary Spectrum Generator to simulate signals from hyper realistic exo-Earths

The atmospheres and surfaces of planets show tremendous amount of spatial variation, which has a direct effect on the spectrum of the object, even if this may not be spatially resolved. Here, we apply hyper realistic radiative simulations of Earth as an exoplanet comprising thousands of simulations and study the unresolved spectrum. The GlobES module on the Planetary Spectrum Generator was used, and we parameterized the atmosphere as described in the modern earth retrospective analysis for research and applications, MERRA2, database. The simulations were made into high spatial resolution images and compared to space based observations from the DSCOVR EPIC, at L1, and Himawari8, geostationary, satellites, confirming spatial variations and the spectral intensities of the simulations. The DSCOVR EPIC camera only functions in narrow wavelength bands, but strong agreement is demonstrated. It is shown that aerosols and small particles play an important role in defining Earths reflectance spectra, contributing significantly to its characteristic blue color. Subsequently, a comprehensive noise model is employed to constrain the exposure time required to detect O2, O3 and H2O as a function of varying ground and cloud cover for several concept observatories, including the habitable worlds observatory. Cloud coverage enhances the detectability of planets in reflected light, with important consequences for the design of the future HWO. The HWO concept would require between 3 to 10 times longer to observe the studied features than LUVOIR A but performs better than the HabEx without a starshade. The codes, routines, and the noise models are made publicly available.

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arXiv2024

Effective & Ethical Mentorship in Physics and Astronomy through Grassroots Organizations

Effective and ethical mentorship practices are crucial to improving recruitment and retention especially for historically minoritized groups (HMGs). Spectrum is a diversity, inclusion, equity, and accessibility (DEIA) grassroots organization committed to empowering equitable excellence through sustainable change. By improving transparency and DEIA within the fields of physics and astronomy, we can empower the next generation of diverse scientists and increase field retention. Starting within our home department at George Mason University and moving outwards, we ensure our students leave as advocates for DEIA and AJEDI (access, justice, equity, diversity, and inclusion) through education and mentorship. Spectrum is providing professionally trained peer mentors to aid students in all facets of their academic and personal lives. Although the peer mentoring program existed since the creation of Spectrum in Spring 2020, we have recently developed and implemented a formal mentorship training for both student and faculty mentors thus increasing the quality, trustworthiness, and confidence of our mentors. Using the latest mentorship research available, this training is developed by Spectrum for George Mason University, with the ability to implement the training at any institution.

physics.ed-ph↗

arXiv2024

Optimized Bandpasses for the Habitable Worlds Observatory's ExoEarth Survey

A primary scientific goal of the future Habitable Worlds Observatory will be the direct detection and characterization of Earth-like planets. Estimates of the exoplanet yields for this concept will help guide mission design through detailed trade studies. It is therefore critical that yield estimation codes optimally adapt observations to the mission's performance parameters to ensure accurate trade studies. To aid in this, we implement wavelength optimization in yield calculations for the first time, allowing the yield code to determine the ideal detection and characterization bandpasses. We use this new capability to confirm the observational wavelength assumptions made for the LUVOIR-B study, namely that the optimum detection wavelength is 500 nm for the majority of targets and the optimum wavelength to detect water is near 1000 nm, given LUVOIR-B's assumed instrument performance parameters. We show that including the wavelength dependent albedo of an Earth twin as a prior provides no significant benefit to the yields of exoEarth candidates and caution against tuning observations to modern Earth twins. We also show that coronagraphs whose inner working angles are similar to step functions may benefit from wavelength optimization and demonstrate how wavelength-dependent instrument performance can impact the optimum wavelengths for detection and characterization. The optimization methods we implement automate wavelength selection and remove uncertainties regarding these choices, helping to adapt the observations to the instrument's performance parameters.

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arXiv2023

Bayesian Analysis for Remote Biosignature Identification on exoEarths (BARBIE) II: Using Grid-Based Nested Sampling in Coronagraphy Observation Simulations for O2 and O3

We present the results for the detectability of the O2 and O3 molecular species in the atmosphere of an Earth-like planet using reflected light at the visible wavelengths. By quantifying the detectability as a function of signal-to-noise ration (SNR), we can constrain the best methods to detect these biosignatures with nest-generation telescopes designed for high-contrast coronagraph. Using 25 bandpasses between 0.515 and 1 micron, and a pre-constructed grid of geometric albedo spectra, we examined the spectral sensitivity needed to detect these species for a range of molecular abundances. We first replicate a modern-Earth twin atmosphere to study the detectability of current O2 and O3 levels, and then expand to a wider range of literature-driven abundances for each molecule. We constrain the optimal 20%, 30%, and 40% bandpasses based on the effective SNR of the data, and define the requirements for the possibility of simultaneous molecular detection. We present our findings of O2 and O3 detectability as functions of SNR, wavelength, and abundance, and discuss how to use these results for optimizing future instrument designs. We find that O2 is detectable between 0.64 and 0.83 micron with moderate-SNR data for abundances near that of modern-Earth and greater, but undetectable for lower abundances consistent with a Proterozoic Earth. O3 is detectable only at very high SNR data in the case of modern-Earth abundances, however it is detectable at low-SNR data for higher O3 abundances that can occur from efficient abiotic O3 production mechanisms.

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arXiv2023

Bayesian Analysis for Remote Biosignature Identification on exoEarths (BARBIE) I: Using Grid-Based Nested Sampling in Coronagraphy Observation Simulations for H2O

Detecting H2O in exoplanet atmospheres is the first step on the path to determining planet habitability. Coronagraphic design currently limits the observing strategy used to detect H2O, requiring the choice of specific bandpasses to optimize abundance constraints. In order to examing the optimal observing strategy for initial characterization of habitable planets using coronagraph-based direct imaging, we quantify the detectability of H2O as a function of signal-to-noise ratio (SNR) and molecular abundance across 25 bandpasses in the visible wavelength range (0.5-1 micron). We use a pre-constructed grid consisting of 1.4 million geometric albedo spectra across a range of abundance and pressure, and interpolate the produce forward models for an efficient nested sampling routine, PSGnest. We first test the detectability of H2O in atmospheres that mimix a modern-Earth twin, and then expand to examine a wider range of H2O abundances; for each abundance value, we constrain the optimal 20% bandpasses based on the effective signal-to-noise ratio (SNR) of the data. We present our findings of H2O detectability as functions of SNR, wavelength, and abundance, and discuss how to use these results for optimizing future coronographic instrument design. We find that there are specific points in wavelength where H2o can be detected down to 0.74 micron with moderate-SNR data for abundances at the upper end of Earth's presumed historical values, while at 0.9 micron, detectability is possible with low-SNR data at modern Earth abundances of H2O.

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arXiv2022

Characterizing and Mitigating the Impact of Telluric Absorption in Precise Radial Velocities

Precise radial velocity (PRV) surveys are important for the search of Earth analogs around nearby bright stars. Such planets induce a small stellar reflex motion with RV amplitude of $\sim$10 cm/s. Detecting such a small RV signal poses important challenges to instrumentation, data analysis, and the precision of astrophysical models to mitigate stellar jitter. In this work, we investigate an important component in the PRV error budget - the spectral contamination from the Earth's atmosphere (tellurics). We characterize the effects of telluric absorption on the RV precision and quantify its contribution to the RV budget over time and across a wavelength range of 350 nm - 2.5$μ$m. We investigate the effectiveness in mitigating tellurics using simulated spectra of a solar twin star with telluric contamination over a year's worth of observations, and we extracted the RVs using two commonly adopted algorithms: dividing out a telluric model before performing cross-correlation or Forward Modeling the observed spectrum incorporating a telluric model. We assume various degrees of cleanness in removing the tellurics, including mimicking the lack of accurate knowledge of the telluric lines by using a mismatched line profile to model the "observed" tellurics. We conclude that the RV errors caused by telluric absorption can be suppressed to close to or even below the photon-limited precision in the optical region, especially in the blue, around 1-10 cm/s. At red through near-infrared wavelengths, however, the residuals of tellurics can induce an RV error on the m/s level even under the most favorable assumptions for telluric removal, leading to significant systematic noise in the RV time series and periodograms. If the red-optical or near-infrared becomes critical in the mitigation of stellar activity, systematic errors from tellurics can be eliminated with a space mission such as EarthFinder.

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arXiv2022

Characterizing and Mitigating Telluric Absorption in Precise Radial Velocities II: A Study of an M2 Type Star

Telluric absorption lines impact measuring precise radial velocities (RVs) from ground-based, high-resolution spectrographs. In this paper, we simulate the dependence of this impact on stellar spectral type and extend the work of the first paper in this series, which studied a G type star, to a synthetic M dwarf star. We quantify the bias in precise RV measurements in the visible and near-infrared (NIR) from the presence of tellurics in a simulated set of observations. We find that M dwarf RVs are more impacted by tellurics compared to G type stars. Specifically, for an M dwarf star, tellurics can induce RV errors of up to 16 cm/s in the red-optical and in excess of 220 cm/s in the NIR. For a G dwarf, comparable RV systematics are 3 cm/s in the red optical and 240 cm/s in the NIR. We attribute this relative increase for M dwarfs stars to the increased concordance in wavelength between telluric lines and stellar Doppler information content. We compare the results of our simulation to data collected on Barnard's star from the iSHELL spectrograph at the NASA Infrared Telescope Facility (IRTF). This study was conducted as a follow-up to the NASA probe mission concept study EarthFinder.

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