arXiv subjects

Anne Dattilo

Publications and source records attributed to Anne Dattilo.

13 recordsLinked to original sources

arXiv2025

Searching for Exoplanets Born Outside the Milky Way: VOYAGERS Survey Design

Observations over the past few decades have found that planets are common around nearby stars in our Galaxy, but little is known about planets that formed outside the Milky Way. We describe the design and early implementation of a survey to test whether planets also exist orbiting the remnant stars of ancient dwarf galaxies that merged with the Milky Way, and if so, how they differ from their Milky Way counterparts. VOYAGERS (Views Of Yore - Ancient Gaia-enceladus Exoplanet Revealing Survey) is a radial velocity (RV) search using precision spectrographs to discover exoplanets orbiting very low metallicity ($-2.8 < [\mathrm{Fe/H}] \leq -0.8$) stars born in the dwarf galaxy Enceladus, which merged with the Milky Way galaxy about 10 Gyr ago. A sample of 22 candidates have been screened from a catalog of Gaia-Enceladus-Sausage (GES) members using a combination of stellar properties and reconnaissance observations from the TRES spectrograph. Precision RV measurements have been initiated using the NEID, HARPS-N, and CARMENES spectrographs. We plan to focus most upcoming observations on 10 main sequence targets. Data collection is well underway, with 778 observations on 22 candidates (385 of which are 10 focus targets), but far from complete. This survey is designed to be sensitive to sub-Neptune mass planets with periods up to hundreds of days. We note that the RV analysis gives mass multiplied by $\sin (inclination)$ or the minimum mass for exoplanets. The expected survey yield is three planets, assuming that occurrence rates are similar to those in the Milky Way and taking into account the degeneracy with inclination in our yield models. Our survey is designed to detect at least one exoplanet if occurrence rates are similar to known Milky Way exoplanets or, if no exoplanets are discovered, to rule out a Milky Way-like planet population in GES with 95% confidence level.

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arXiv2025

Are We There Yet? Challenges in Quantifying the Frequency of Earth Analogs in the Habitable Zone

Searching for life elsewhere in the universe is one of the most highly prioritized pursuits in astronomy today. However, the ability to observe evidence of Earth-like life through biosignatures is limited by the number of planets in the solar neighborhood with conditions similar to Earth. The occurrence rate of Earth-like planets in the habitable zones of Sun-like stars, $\eta_{\oplus}$, is therefore crucial for addressing the apparent lack of consensus on its value in the literature. Here we present a review of the current understanding of $\eta_{\oplus}$. We first provide definitions for parameters that contribute to $\eta_{\oplus}$. Then, we discuss the previous and current estimated parameter values and the context of the limitations on the analyses that produced these estimates. We compile an extensive list of the factors that go into any calculation of $\eta_{\oplus}$, and how detection techniques and surveys differ in their sensitivity and ability to accurately constrain $\eta_{\oplus}$. Understanding and refining the value of $\eta_{\oplus}$ is crucial for upcoming missions and telescopes, such as the planned Habitable Worlds Observatory and the Large Interferometer for Exoplanets, which aim to search for biosignatures on exoplanets in the solar neighborhood.

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arXiv2025

The First Occurrence Rate Estimates for Exoplanets in Small-Separation Binary Star Systems: Planet Occurrence is Suppressed in Binary Stars

Exoplanet occurrence rates facilitate comparisons between observations of planets and theoretical models of planet formation. Despite their deductive power, exoplanet occurrence rates for half the stars in the sky are missing because occurrence rate studies systematically exclude binary star systems. We assembled a large sample of high-likelihood binaries from the Kepler mission to calculate occurrence rates for circumstellar (S-type) planets in small-separation binary star systems ($\lesssim 100$ au) for the first time. For a sample of high-likelihood small-separation binaries, we found binaries to host 58% fewer planets per system than single stars to 11.4$\sigma$ significance within 1-4 $R_{\oplus}$ and 1-50 d, and 50% fewer planets compared to single stars when integrating over the full parameter space of 1-10 $R_{\oplus}$ and 1-100 d to 3.8$\sigma$ significance.. We found no evidence for a radius valley or radius cliff, instead detecting a smooth decline in planet occurrence with increasing planetary radius. The difference between the single-star planet radius distribution and the binary-star planet radius distribution is 4.3$\sigma$ significant from a Kolomogorov-Smirnov test. These results suggest significantly different planet formation and survival outcomes in binaries compared to single stars, and support other studies that have measured a deficit of observed planets in binary star systems.

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arXiv2025

THYME XIII: Two young Neptunes orbiting a 75-Myr star in the Alpha Persei Cluster

Young planets with mass measurements are particularly valuable in studying atmospheric mass-loss processes, but these planets are rare and their masses difficult to measure due to stellar activity. We report the discovery of a planetary system around TOI-6109, a young, 75 Myr-old Sun-like star in the Alpha Persei cluster. It hosts at least two transiting Neptune-like planets. Using three TESS sectors, 30 CHEOPS orbits, and photometric follow-up observations from the ground, we confirm the signals of the two planets. TOI-6109 b has an orbital period of P=$5.6904^{+0.0004}_{-0.0004}$ days and a radius of R=$4.87^{+0.16}_{-0.12}$ R$_\oplus$. The outer planet, TOI-6109 c has an orbital period of P=$8.5388^{+0.0006}_{-0.0005}$ days and a radius of R=$4.83^{+0.07}_{-0.06}$ R$_\oplus$. These planets orbit just outside a 3:2 mean motion resonance. The near-resonant configuration presents the opportunity to measure the planet's mass via TTV measurements and to bypass difficult RV measurements. Measuring the masses of the planets in this system will allow us to test theoretical models of atmospheric mass loss.

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arXiv2025

JWST COMPASS: NIRSpec/G395H Transmission Observations of the Super-Earth TOI-776b

We present two transit observations of the $\sim$520K, 1.85R$_\oplus$, 4.0M$_\oplus$ super-Earth TOI-776b with JWST NIRSpec/G395H, resulting in a 2.8-5.2$\mu$m transmission spectrum. Producing reductions using the ExoTiC-JEDI and Eureka! pipelines, we obtain a median transit depth precision of 34ppm for both visits and both reductions in spectroscopic channels 30 pixels wide ($\sim$0.02$\mu$m). We find that our independent reductions produce consistent transmission spectra, however, each visit shows differing overall structure. For both reductions, a flat line is preferred for Visit 1 while a flat line with an offset between the NRS1 and NRS2 detectors is preferred for Visit 2; however, we are able to correct for this offset during our modeling analysis following methods outlined in previous literature. Using picaso forward models, we can rule out metallicities up to at least 100$\times$ solar with an opaque pressure of 10$^{-3}$ bar to $\geq$3$\sigma$ in all cases, however, the exact lower limit varies between the visits, with Visit 1 ruling out $\lesssim$100$\times$ solar while the lower limits for Visit 2 extend beyond $\sim$350$\times$ solar. Our results add to the growing list of super-Earth atmospheric constraints by JWST, which provide critical insight into the diversity and challenges of characterizing terrestrial planets.

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arXiv2024

JWST COMPASS: The first near- to mid-infrared transmission spectrum of the hot super-Earth L 168-9 b

We present the first broadband near- to mid-infrared (3-12 microns) transmission spectrum of the highly-irradiated (T_eq = 981 K) M dwarf rocky planet L 168-9 b (TOI-134 b) observed with the NIRSpec and MIRI instruments aboard JWST. We measure the near-infrared transit depths to a combined median precision of 20 ppm across the three visits in 54 spectroscopic channels with uniform widths of 60 pixels (~0.2 microns wide; R~100), and the mid-infrared transit depths to 61 ppm median precision in 48 wavelength bins (~0.15 microns wide; R~50). We compare the transmission spectrum of L 168-9 b to a grid of 1D thermochemical equilibrium forward models, and rule out atmospheric metallicities of less than 100x solar (mean molecular weights <4 g mol$^{-1}$) to 3-sigma confidence assuming high surface pressure (>1 bar), cloudless atmospheres. Based on photoevaporation models for L 168-9 b with initial atmospheric mass fractions ranging from 2-100%, we find that this planet could not have retained a primordial H/He atmosphere beyond the first 200 Myr of its lifetime. Follow-up MIRI eclipse observations at 15 microns could make it possible to confidently identify a CO2-dominated atmosphere on this planet if one exists.

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arXiv2024

A Unified Treatment of Kepler Occurrence to Trace Planet Evolution II: The Radius Cliff Formed by Atmospheric Escape

The Kepler mission enabled us to look at the intrinsic population of exoplanets within our galaxy. In period-radius space, the distribution of the intrinsic population of planets contains structure that can trace planet formation and evolution history. The most distinctive feature in period-radius space is the radius cliff, a steep drop-off in occurrence between $2.5-4$R$_\oplus$ across all period ranges, separating the sub-Neptune population from the rarer Neptunes orbiting within 1 au. Following our earlier work to measure the occurrence rate of the Kepler population, we characterize the shape of the radius cliff as a function of orbital period ($10-300$ days) as well as insolation flux (9500S$_\oplus$ -- 10S$_\oplus$). The shape of the cliff flattens at longer orbital periods, tracking the rising population of Neptune-sized planets. In insolation, however, the radius cliff is both less dramatic and the slope is more uniform. The difference in this feature between period- and insolation-space can be linked to the effect of EUV/X-ray versus bolometric flux in the planet's evolution. Models of atmospheric mass loss processes that predict the location and shape of the radius valley also predict the radius cliff. We compare our measured occurrence rate distribution to population synthesis models of photoevaporation and core-powered mass-loss in order to constrain formation and evolution pathways. We find that the models do not statistically agree with our occurrence distributions of the radius cliff in period- or insolation-space. Atmospheric mass loss that shapes the radius valley cannot fully explain the shape of the radius cliff.

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arXiv2023

Deformable mirror-based pupil chopping for exoplanet imaging and adaptive optics

Due to turbulence in the atmosphere images taken from ground-based telescopes become distorted. With adaptive optics (AO) images can be given greater clarity allowing for better observations with existing telescopes and are essential for ground-based coronagraphic exoplanet imaging instruments. A disadvantage to many AO systems is that they use sensors that can not correct for non-common path aberrations. We have developed a new focal plane wavefront sensing technique to address this problem called deformable mirror (DM)-based pupil chopping. The process involves a coronagraphic or non-coronagraphic science image and a deformable mirror, which modulates the phase by applying a local tip/tilt every other frame which enables correcting for leftover aberrations in the wavefront after a conventional AO correction. We validate this technique with both simulations (for coronagraphic and non-coronagraphic images) and testing (for non-coronagraphic images) on UCSC's Santa Cruz Extreme AO Laboratory (SEAL) testbed. We demonstrate that with as low as 250 nm of DM stroke to apply the local tip/tilt this wavefront sensor is linear for low-order Zernike modes and enables real-time control, in principle up to kHz speeds to correct for residual atmospheric turbulence.

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arXiv2023

A Unified Treatment of Kepler Occurrence to Trace Planet Evolution I: Methodology

We present Kepler exoplanet occurrence rates for planets between $0.5-16$ R$_\oplus$ and between $1-400$ days. To measure occurrence, we use a non-parametric method via a kernel density estimator and use bootstrap random sampling for uncertainty estimation. We use a full characterization of completeness and reliability measurements from the Kepler DR25 catalog, including detection efficiency, vetting completeness, astrophysical- and false alarm reliability. We also include more accurate and homogeneous stellar radii from Gaia DR2. In order to see the impact of these final Kepler properties, we revisit benchmark exoplanet occurrence rate measurements from the literature. We compare our measurements with previous studies to both validate our method and observe the dependence of these benchmarks on updated stellar and planet properties. For FGK stars, between $0.5-16$ R$_\oplus$ and between $1-400$ days, we find an occurrence of $1.52\pm0.08$ planets per star. We investigate the dependence of occurrence as a function of radius, orbital period, and stellar type and compare with previous studies with excellent agreement. We measure the minimum of the radius valley to be $1.78^{+0.14}_{-0.16}$ R$_\oplus$ for FGK stars and find it to move to smaller radii for cooler stars. We also present new measurements of the slope of the occurrence cliff at $3-4$ R$_\oplus$, and find that the cliff becomes less steep at long orbital period. Our methodology will enable us to constrain theoretical models of planet formation and evolution in the future.

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arXiv2023

The TESS-Keck Survey. XVI. Mass Measurements for 12 Planets in Eight Systems

With JWST's successful deployment and unexpectedly high fuel reserves, measuring the masses of sub-Neptunes transiting bright, nearby stars will soon become the bottleneck for characterizing the atmospheres of small exoplanets via transmission spectroscopy. Using a carefully curated target list and more than two years' worth of APF-Levy and Keck-HIRES Doppler monitoring, the TESS-Keck Survey is working toward alleviating this pressure. Here we present mass measurements for 11 transiting planets in eight systems that are particularly suited to atmospheric follow-up with JWST. We also report the discovery and confirmation of a temperate super-Jovian-mass planet on a moderately eccentric orbit. The sample of eight host stars, which includes one subgiant, spans early-K to late-F spectral types ($T_\mathrm{eff} =$ 5200--6200 K). We homogeneously derive planet parameters using a joint photometry and radial velocity modeling framework, discuss the planets' possible bulk compositions, and comment on their prospects for atmospheric characterization.

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arXiv2023

Identifying Exoplanets with Deep Learning. V. Improved Light Curve Classification for TESS Full Frame Image Observations

The TESS mission produces a large amount of time series data, only a small fraction of which contain detectable exoplanetary transit signals. Deep learning techniques such as neural networks have proved effective at differentiating promising astrophysical eclipsing candidates from other phenomena such as stellar variability and systematic instrumental effects in an efficient, unbiased and sustainable manner. This paper presents a high quality dataset containing light curves from the Primary Mission and 1st Extended Mission full frame images and periodic signals detected via Box Least Squares (Kov\'acs et al. 2002; Hartman 2012). The dataset was curated using a thorough manual review process then used to train a neural network called Astronet-Triage-v2. On our test set, for transiting/eclipsing events we achieve a 99.6% recall (true positives over all data with positive labels) at a precision of 75.7% (true positives over all predicted positives). Since 90% of our training data is from the Primary Mission, we also test our ability to generalize on held-out 1st Extended Mission data. Here, we find an area under the precision-recall curve of 0.965, a 4% improvement over Astronet-Triage (Yu et al. 2019). On the TESS Object of Interest (TOI) Catalog through April 2022, a shortlist of planets and planet candidates, Astronet-Triage-v2 is able to recover 3577 out of 4140 TOIs, while Astronet-Triage only recovers 3349 targets at an equal level of precision. In other words, upgrading to Astronet-Triage-v2 helps save at least 200 planet candidates from being lost. The new model is currently used for planet candidate triage in the Quick-Look Pipeline (Huang et al. 2020a,b; Kunimoto et al. 2021).

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arXiv2019

Identifying Exoplanets with Deep Learning III: Automated Triage and Vetting of TESS Candidates

NASA's Transiting Exoplanet Survey Satellite (TESS) presents us with an unprecedented volume of space-based photometric observations that must be analyzed in an efficient and unbiased manner. With at least $\sim1,000,000$ new light curves generated every month from full frame images alone, automated planet candidate identification has become an attractive alternative to human vetting. Here we present a deep learning model capable of performing triage and vetting on TESS candidates. Our model is modified from an existing neural network designed to automatically classify Kepler candidates, and is the first neural network to be trained and tested on real TESS data. In triage mode, our model can distinguish transit-like signals (planet candidates and eclipsing binaries) from stellar variability and instrumental noise with an average precision (the weighted mean of precisions over all classification thresholds) of 97.0% and an accuracy of 97.4%. In vetting mode, the model is trained to identify only planet candidates with the help of newly added scientific domain knowledge, and achieves an average precision of 69.3% and an accuracy of 97.8%. We apply our model on new data from Sector 6, and present 288 new signals that received the highest scores in triage and vetting and were also identified as planet candidates by human vetters. We also provide a homogeneously classified set of TESS candidates suitable for future training.

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arXiv2019

Identifying Exoplanets with Deep Learning II: Two New Super-Earths Uncovered by a Neural Network in K2 Data

For years, scientists have used data from NASA's Kepler Space Telescope to look for and discover thousands of transiting exoplanets. In its extended K2 mission, Kepler observed stars in various regions of sky all across the ecliptic plane, and therefore in different galactic environments. Astronomers want to learn how the population of exoplanets are different in these different environments. However, this requires an automatic and unbiased way to identify the exoplanets in these regions and rule out false positive signals that mimic transiting planet signals. We present a method for classifying these exoplanet signals using deep learning, a class of machine learning algorithms that have become popular in fields ranging from medical science to linguistics. We modified a neural network previously used to identify exoplanets in the Kepler field to be able to identify exoplanets in different K2 campaigns, which range in galactic environments. We train a convolutional neural network, called AstroNet-K2, to predict whether a given possible exoplanet signal is really caused by an exoplanet or a false positive. AstroNet-K2 is highly successful at classifying exoplanets and false positives, with accuracy of 98% on our test set. It is especially efficient at identifying and culling false positives, but for now, still needs human supervision to create a complete and reliable planet candidate sample. We use AstroNet-K2 to identify and validate two previously unknown exoplanets. Our method is a step towards automatically identifying new exoplanets in K2 data and learning how exoplanet populations depend on their galactic birthplace.

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