arXiv subjects

Matthew Penny

Publications and source records attributed to Matthew Penny.

At least 19 recordsLinked to original sources

arXiv2026

A Minute-Cadence Deep Bulge Survey: First Data Release of DREAMS

The DECam Rogue Earths and Mars Survey (DREAMS), a NOIRLab survey program, has been conducting a three-year survey covering a 5 deg$^2$ area in the Galactic bulge (roughly spanning $-1.2^\circ \lesssim \ell \lesssim +2.1^\circ$ and $-2.8^\circ \lesssim b \lesssim -0.6^\circ$) since 2025 June. Its primary science goal is to detect low-mass free-floating planets through microlensing, while its minute-level cadence ($20-40\,\mathrm{hr}^{-1}$ in $z$ band and $4-8\,\mathrm{hr}^{-1}$ in $r$ band) also enables the detection and characterization of rapid phenomena on timescales of minutes to hours such as stellar flares and pulsating stars. The survey reaches a single-exposure depth of $z_{\rm AB}\sim 22$ mag, about two magnitudes deeper than previous bulge time-domain surveys. We present the data reduction and calibration of the DREAMS observations obtained in 2025 and introduce the first DREAMS data release (DR1). DR1 includes 1,856 $z$-band observations and 325 $r$-band observations for 59,372,789 stars. The DREAMS DR1 catalog contains about twice as many stars as previous catalog covering the same 5 deg$^2$ area. We present DREAMS light curves for a known blue large-amplitude pulsator (BLAP) and a known low-amplitude transiting system to demonstrate the survey's capabilities. We also perform a pilot search for short-duration variables over about 0.4% of the DR1 sample, identifying one new short microlensing event, two stellar flares, and 24 new short variables. This suggests that DREAMS DR1 may contain hundreds of stellar flares and thousands of previously unknown short variables.

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arXiv2026

KMT-2025-BLG-1616Lb: First Microlensing Bound Planet From DREAMS

We present observations and analysis of the bound planetary microlensing event KMT-2025-BLG-1616. The planetary signal was captured by the Korea Microlensing Telescope Network (KMTNet) and the DECam Rogue Earths and Mars Survey (DREAMS). DREAMS's minute-cadence observations break the central/resonant degeneracy in the binary-lens models. The color of the faint source star ($I=22$) is measured from the DREAMS's $r - z$ color. The planetary system has a planet-host mass ratio of $q \sim 5 \times 10^{-4}$. A Bayesian analysis yields a host-star mass of $\sim 0.3\,M_\odot$, a planetary mass of $\sim 40\,M_{\oplus}$, a projected planet-host separation of $\sim 1.6~\mathrm{au}$, and a lens distance of $\sim 7.5~\mathrm{kpc}$. Based on the photometric precision achieved by DREAMS for this event, we simulate free-floating planet (FFP) detections and find that DREAMS is sensitive to Mars-mass FFPs in the Galactic bulge and Moon-mass FFPs in the Galactic disk.

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arXiv2025

Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey. V. Detection Rates of Multiplanetary Systems in High Magnification Microlensing Events

The Nancy Grace Roman Space Telescope will expand the reach of gravitational microlensing surveys by increasing the number of events monitored and the precision of their light curves. We investigate Roman's ability to detect triple-lens microlensing systems, cases where a foreground star with two bound exoplanets produces detectable anomalies in a microlensing event, using its planned high-cadence observations toward the Galactic bulge. We simulate a large set of high-magnification microlensing light curves based on Roman's expected survey characteristics. A detection criterion, based on a required $\chi^2$ improvement for a two-planet model, is applied to determine whether the second planet can be reliably distinguished from a single-planet (binary-lens) model. Our simulations show that the majority of two-planet microlensing events would be detectable with Roman. Events in which both planets are relatively massive (planet-star mass ratios of order $10^{-3}$), or in which the more massive planet occupies a favorable resonant configuration, produce strong central perturbations, resulting in detection efficiencies of roughly 90\%. By contrast, systems with only low-mass planets ($q \sim 10^{-4}$) or with less favorable alignments generate much weaker signals, which often fall below the detection threshold. In general, the planetary mass ratios and the resulting caustic geometry (e.g., central caustic size in resonant versus wide/close orbits) are the dominant factors governing detectability. Taking into account the expected frequency of planetary systems and the fraction of high-magnification events, we estimate that Roman will detect a high-magnification triple-lens event in approximately 4.5\% of multi-planet microlensing events, corresponding to about 64 events over the course of the full survey.

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arXiv2025

Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey. IV. Lens Mass and Distance Measurements

As part of the Galactic Bulge Time Domain Survey (GBTDS), the Nancy Grace Roman Galactic Exoplanet Survey (RGES) will use microlensing to discover cold outer planets and free-floating planets unbound to stars. NASA has established several science requirements for the GBTDS to ensure RGES success. A key advantage of RGES is Roman's high angular resolution, which will allow detection of flux from many host stars. One requirement specifies that Roman must measure the masses and distances of 40% of detected planet hosts with 20% precision or better. To test this, we simulated microlensing events toward the GBTDS fields and used Fisher matrix analysis to estimate light curve parameter uncertainties. Combining these with Roman imaging observables (lens flux, relative lens-source proper motion), we estimated the achievable precision of lens mass and distance measurements. Using pyLIMASS, a publicly available code for estimating lens properties, we applied this analysis to 3,000 simulated events. Assuming the Cassan et al. (2012) exoplanet mass function, we find that >40% of host stars meet the required 20% precision threshold, confirming that the GBTDS can satisfy the mission requirement. We validated our approach by comparing our inferred lens masses and distances to empirical measurements from detailed image-constrained light curve modeling of historical microlensing events with Hubble and Keck follow-up imaging. Our results agree within roughly 1 sigma, demonstrating that both approaches yield consistent and reliable mass and distance estimates, and confirming the robustness of our simulations for Roman-era microlensing science.

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arXiv2025

Technique-agnostic exoplanet demography for the Roman era -- I. Testing a demography retrieval framework using simulated Kepler-like transit datasets

The Nancy Grace Roman Space Telescope (Roman) will unveil for the first time the full architecture of planetary systems across Galactic distances through the discovery of up to 200,000 cool and hot exoplanets using microlensing and transit detection methods. Roman's huge exoplanet haul, and Galactic reach, will require new methods to leverage the full exoplanet demographic content of the combined microlensing and transit samples, given the different sensitivity bias of the techniques to planet and host properties and Galactic location. We present a framework for technique-agnostic exoplanet demography (TAED) that can allow large, multi-technique exoplanet samples distributed over Galactic distance scales to be combined for demographic studies. Our TAED forward modelling and retrieval framework uses parameterised model exoplanet demographic distributions to embed planetary systems within a stellar population synthesis model of the Galaxy, enabling internally consistent forecasts to be made for all detection methods that are based on spatio-kinematic system properties. In this paper, as a first test of the TAED framework, we apply it to simulated transit datasets based on the Kepler Data Release 25 to assess parameter recovery accuracy and method scalability for a single large homogeneous dataset. We find that optimisation using differential evolution provides a computationally scalable framework that gives a good balance between computational efficiency and accuracy of parameter recovery.

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arXiv2024

SynthPop: A New Framework for Synthetic Milky Way Population Generation

We present SynthPop, a new open source, modular population synthesis Galactic modeling software to simulate catalogs of Milky Way stars along any sightline outward from the Sun. Motivated by a lack flexibility in existing Galactic models, SynthPop is coded entirely in python, can be run standalone or as an imported module, and is configured by json files that allow different model components to be switched out as desired. We describe the modular code structure, how the population generation process runs, and how to use the code. We also present model validation testing and known inaccuracies, and present an example of the code use, comparing Gaia data and the Gaia Universe Model Snapshot to a SynthPop implementation. The code is available now via GitHub with ReadTheDocs documentation and can be installed via pip.

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arXiv2023

Magnifying NASA Roman GBTDS exoplanet science with coordinated observations by ESA Euclid

The ESA Euclid mission is scheduled to launch on July 1st 2023. This White Paper discusses how Euclid observations of the Galactic Bulge Time Domain Survey (GBTDS) area could dramatically enhance the exoplanet science output of the Nancy Grace Roman Space Telescope (Roman). An early Euclid pre-imaging survey of the Roman GBTDS fields, conducted soon after launch, can improve proper motion determinations for Roman exoplanet microlenses that can yield a factor of up to $\sim 5$ improvement in exoplanet mass measurements. An extended Euclid mission would also enable the possibility of sustained simultaneous observations of the GBTDS by Euclid and Roman that would achieve large gains in several areas of Roman exoplanet science, including science that is impossible to achieve with Roman alone. These include: a comprehensive demographic survey for free-floating planets that includes precision mass measurements to establish the true nature of individual candidates; detection, confirmation and mass measurements of exomoons; direct exoplanet mass measurements through parallax and finite source size effects for a large sample of bound exoplanets detected jointly by Euclid and Roman; enhanced false-positive discrimination for the large samples of transiting planets that Roman will detect. Our main recommendation to NASA and ESA is to initiate a Joint Study Group as early as possible that can examine how both missions could best conduct a coordinated campaign. We also encourage flexibility in the GBTDS scheduling.

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arXiv2022

Euclid-Roman joint microlensing survey: early mass measurement, free floating planets and exomoons

As the Kepler mission has done for hot exoplanets, the ESA Euclid and NASA Roman missions have the potential to create a breakthrough in our understanding of the demographics of cool exoplanets, including unbound, or "free-floating", planets (FFPs). In this study, we demonstrate the complementarity of the two missions and propose two joint-surveys to better constrain the mass and distance of microlensing events. We first demonstrate that an early brief Euclid survey (7 h) of the Roman microlensing fields will allow the measurement of a large fraction of events relative proper motions and lens magnitudes. Then, we study the potential of simultaneous observations by Roman and Euclid to enable the measurement of the microlensing parallax for the shortest microlensing events. Using detailed simulations of the joint detection yield we show that within one year Roman-Euclid observations will be at least an order of magnitude more sensitive than current ground-based measurements. Depending on the exact distribution of FFP, a joint Roman-Euclid campaign should detect around 130 FFP events within a year, including 110 with measured parallax that strongly constrain the FFP mass, and around 30 FFP events with direct mass and distance measurements. The ability of the joint survey to completely break the microlens mass-distance-velocity degeneracy for a significant subset of events provides a unique opportunity to verify unambiguously the FFP hypothesis or else place abundance limits for FFPs between Earth and Jupiter masses that are up to two orders of magnitude stronger than provided by ground-based surveys. Finally, we study the capabilities of the joint survey to enhance the detection and charcterization of exomoons, and found that it could lead to the detection of the first exomoon.

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arXiv2022

An Isolated Stellar-Mass Black Hole Detected Through Astrometric Microlensing

We report the first unambiguous detection and mass measurement of an isolated stellar-mass black hole (BH). We used the Hubble Space Telescope (HST) to carry out precise astrometry of the source star of the long-duration (t_E~270 days), high-magnification microlensing event MOA-2011-BLG-191/OGLE-2011-BLG-0462 (hereafter designated as MOA-11-191/OGLE-11-462), in the direction of the Galactic bulge. HST imaging, conducted at eight epochs over an interval of six years, reveals a clear relativistic astrometric deflection of the background star's apparent position. Ground-based photometry of MOA-11-191/OGLE-11-462 shows a parallactic signature of the effect of the Earth's motion on the microlensing light curve. Combining the HST astrometry with the ground-based light curve and the derived parallax, we obtain a lens mass of 7.1 +/- 1.3 Msun and a distance of 1.58 +/- 0.18 kpc. We show that the lens emits no detectable light, which, along with having a mass higher than is possible for a white dwarf or neutron star, confirms its BH nature. Our analysis also provides an absolute proper motion for the BH. The proper motion is offset from the mean motion of Galactic-disk stars at similar distances by an amount corresponding to a transverse space velocity of ~45 km/s, suggesting that the BH received a 'natal kick' from its supernova explosion. Previous mass determinations for stellar-mass BHs have come from radial-velocity measurements of Galactic X-ray binaries, and from gravitational radiation emitted by merging BHs in binary systems in external galaxies. Our mass measurement is the first for an isolated stellar-mass BH using any technique.

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arXiv2021

KMT-2021-BLG-0912Lb: A microlensing super Earth around a K-type star

The light curve of the microlensing event KMT-2021-BLG-0912 exhibits a very short anomaly relative to a single-lens single-source form. We investigate the light curve for the purpose of identifying the origin of the anomaly. We model the light curve under various interpretations. From this, we find four solutions, in which three solutions are found under the assumption that the lens is composed of two masses (2L1S models), and the other solution is found under the assumption that the source is comprised of a binary-star system (1L2S model). The 1L2S model is ruled out based on the contradiction that the faint source companion is bigger than its primary, and one of the 2L1S solutions is excluded from the combination of the relatively worse fit, blending constraint, and lower overall probability, leaving two surviving solutions with the planet/host mass ratios of $q\sim 2.8\times 10^{-5}$ and $\sim 1.1\times 10^{-5}$. A subtle central deviation supports the possibility of a tertiary lens component, either a binary companion to the host with a very large or small separation or a second planet lying near the Einstein ring, but it is difficult to claim a secure detection due to the marginal fit improvement, lack of consistency among different data sets, and difficulty in uniquely specifying the nature of the tertiary component. With the observables of the event, it is estimated that the masses of the planet and host are $\sim (6.9~M_\oplus, 0.75~M_\odot)$ according to one solution and $\sim (2.8~M_\oplus, 0.80~M_\odot)$ according to the other solution, indicating that the planet is a super Earth around a K-type star, regardless of the solution.

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arXiv2021

Classifying High-cadence Microlensing Light Curves I; Defining Features

Microlensing is a powerful tool for discovering cold exoplanets, and the The Roman Space Telescope microlensing survey will discover over 1000 such planets. Rapid, automated classification of Roman's microlensing events can be used to prioritize follow-up observations of the most interesting events. Machine learning is now often used for classification problems in astronomy, but the success of such algorithms can rely on the definition of appropriate features that capture essential elements of the observations that can map to parameters of interest. In this paper, we introduce tools that we have developed to capture features in simulated Roman light curves of different types of microlensing events, and evaluate their effectiveness in classifying microlensing light curves. These features are quantified as parameters that can be used to decide the likelihood that a given light curve is due to a specific type of microlensing event. This method leaves us with a list of parameters that describe features like the smoothness of the peak, symmetry, the number of peaks, and width and height of small deviations from the main peak. This will allow us to quickly analyze a set of microlensing light curves and later use the resulting parameters as input to machine learning algorithms to classify the events.

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arXiv2019

WFIRST and EUCLID: enabling the microlensing parallax measurement from space

The Wide Field Infrared Survey Telescope (WFIRST) is expected to detect hundreds of free-floating planets, but it will not be able to measure their masses. However, simultaneous microlensing observations by both Euclid and WFIRST spacecraft, separated by ~ 100, 000 km in orbits around the Sun-Earth L2 Lagrange point, will enable measurements of microlensing parallax for low-mass lenses such as free-floating planets. Using simple Fisher matrix estimates of the parallax measurement uncertainties, we show that high-cadence observations by Euclid could be used to measure ~ 1 free-floating planet microlens parallax per 6 days of simultaneous Euclid observations. Accounting for Euclid's pointing constraints, it could therefore potentially measure ~ 20 free-floating planet parallaxes with 120 days of observations split equally between Euclid's main mission and an extended mission, with a potential to increase this number if spacecraft pointing constraints can be relaxed after the end of the main mission. These Euclid observations would also provide additional mass measurements or cross-checks for larger numbers of WFIRST's bound planets, among other benefits to several science cases.

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arXiv2019

Community Involvement in the WFIRST Exoplanet Microlensing Survey

WFIRST is NASA's first flagship mission with pre-defined core science programs to study dark energy and perform a statistical census of wide orbit exoplanets with a gravitational microlensing survey. Together, these programs are expected to use more than half of the prime mission observing time. Previously, only smaller, PI-led missions have had core programs that used such a large fraction of the observing time, and in many cases, the data from these PI-led missions was reserved for the PI's science team for a proprietary period that allowed the PI's team to make most of the major discoveries from the data. Such a procedure is not appropriate for a flagship mission, which should provide science opportunities to the entire astronomy community. For this reason, there will be no proprietary period for WFIRST data, but we argue that a larger effort to make WFIRST science accessible to the astronomy community is needed. We propose a plan to enhance community involvement in the WFIRST exoplanet microlensing survey in two different ways. First, we propose a set of high level data products that will enable astronomers without detailed microlensing expertise access to the statistical implications of the WFIRST exoplanet microlensing survey data. And second, we propose the formation of a WFIRST Exoplanet Microlensing Community Science Team that will open up participation in the development of the WFIRST exoplanet microlensing survey to the general astronomy community in collaboration for the NASA selected science team, which will have the responsibility to provide most of the high level data products. This community science team will be open to volunteers, but members should also have the opportunity to apply for funding.

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arXiv2019

Wide-Orbit Exoplanet Demographics

The Kepler, K2 and TESS transit surveys are revolutionizing our understanding of planets orbiting close to their host stars and our understanding of exoplanet systems in general, but there remains a gap in our understanding of wide-orbit planets. This gap in our understanding must be filled if we are to understand planet formation and how it affects exoplanet habitability. We summarize current and planned exoplanet detection programs using a variety of methods: microlensing (including WFIRST), radial velocities, Gaia astrometry, and direct imaging. Finally, we discuss the prospects for joint analyses using results from multiple methods and obstacles that could hinder such analyses. We endorse the findings and recommendations published in the 2018 National Academy report on Exoplanet Science Strategy. This white paper extends and complements the material presented therein.

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arXiv2019

The Scientific Context of WFIRST Microlensing in the 2020s

[abridged] WFIRST is uniquely capable of finding planets with masses as small as Mars at separations comparable to Jupiter, i.e., beyond the current ice lines of their stars. These planets fall between the close-in planets found by Kepler and the wide separation gas giants seen by direct imaging and ice giants inferred from ALMA observations. Furthermore, the smallest planets WFIRST can detect are smaller than the planets probed by RV and Gaia at comparable separations. Interpreting planet populations to infer the underlying formation and evolutionary processes requires combining results from multiple detection methods to measure the full variation of planets as a function of planet size, orbital separation, and host star mass. Microlensing is the only way to find planets from 0.5 to 5M_E at 1 to 5au. The case for a microlensing survey from space has not changed in the past 20 yrs: space allows wide-field diffraction-limited observations that resolve main-sequence stars in the bulge, which allows the detection and characterization of the smallest signals including those from planets with masses at least as small as Mars. What has changed is that ground-based (GB) microlensing is reaching its limits, underscoring the scientific necessity for a space-based survey. GB microlensing has found a break in the mass-ratio distribution at about a Neptune, implying that these are the most common microlensing planet and that planets smaller than this are rare. However, GB microlensing reaches its detection limits only slightly below the observed break. WFIRST will measure the shape of the mass-ratio function below the break by finding numerous smaller planets: 500 Neptunes, 600 gas giants, 200 Earths, and planets as small as 0.1M_E. Because it will also measure host masses and distances, WFIRST will also track the behavior of the planet distribution as a function of separation and host star mass.

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arXiv2019

KELT-23Ab: A Hot Jupiter Transiting a Near-Solar Twin Close to the TESS and JWST Continuous Viewing Zones

We announce the discovery of KELT-23Ab, a hot Jupiter transiting the relatively bright ($V=10.3$) star BD+66 911 (TYC 4187-996-1), and characterize the system using follow-up photometry and spectroscopy. A global fit to the system yields host-star properties of $T_{eff}=5900\pm49 K$, $M_*=0.945^{+0.060}_{-0.054} M_{\odot}$, $R_*=0.995\pm0.015 R_{\odot}$, $L_*=1.082^{+0.051}_{-0.048} L_{\odot}$, log$g_{*}=4.418^{+0.026}_{-0.025}$ (cgs), and $\left[{\rm Fe}/{\rm H}\right]=-0.105\pm0.077$. KELT-23Ab is a hot Jupiter with mass $M_P=0.938^{+0.045}_{-0.042} M_{\rm J}$, radius $R_P=1.322\pm0.025 R_{\rm J}$, and density $\rho_P=0.504^{+0.038}_{-0.035}$ g cm$^{-3}$. Intense insolation flux from the star has likely caused KELT-23Ab to become inflated. The time of inferior conjunction is $T_0=2458149.40776\pm0.00091~\rm {BJD_{TDB}}$ and the orbital period is $P=2.255353^{+0.000031}_{-0.000030}$ days. There is strong evidence that KELT-23A is a member of a long-period binary star system with a less luminous companion, and due to tidal interactions, the planet is likely to spiral into its host within roughly a Gyr. This system has one of the highest positive ecliptic latitudes of all transiting planet hosts known to date, placing it near the Transiting Planet Survey Satellite and James Webb Space Telescope continuous viewing zones. Thus we expect it to be an excellent candidate for long-term monitoring and follow-up with these facilities.

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arXiv2019

A Fast Approximate Approach to Microlensing Survey Analysis

Microlensing can be used to discover exoplanets of a wide range of masses with orbits beyond ~ 1 AU, and even free-floating planets. The WFIRST mission will use microlensing to discover approximately 1600 planets by monitoring ~100 million stars to find ~50000 microlensing events. Modelling each microlensing event, especially the ones involving two or more lenses, is typically complicated and time-consuming, and analyzing thousands of WFIRST microlensing events is possibly infeasible using current methods. Here, we present an algorithm that is able to rapidly evaluate thousands of simulated WFIRST binary-lens microlensing light curves, returning an estimate for the physical parameters of the lens systems. We find that this algorithm can recover projected separations between the planet and the star very well for low-mass-ratio events, and can also estimate mass ratios within an order of magnitude for events with wide and close caustic topologies.

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arXiv2019

The Wide Field Infrared Survey Telescope: 100 Hubbles for the 2020s

The Wide Field Infrared Survey Telescope (WFIRST) is a 2.4m space telescope with a 0.281 deg^2 field of view for near-IR imaging and slitless spectroscopy and a coronagraph designed for > 10^8 starlight suppresion. As background information for Astro2020 white papers, this article summarizes the current design and anticipated performance of WFIRST. While WFIRST does not have the UV imaging/spectroscopic capabilities of the Hubble Space Telescope, for wide field near-IR surveys WFIRST is hundreds of times more efficient. Some of the most ambitious multi-cycle HST Treasury programs could be executed as routine General Observer (GO) programs on WFIRST. The large area and time-domain surveys planned for the cosmology and exoplanet microlensing programs will produce extraordinarily rich data sets that enable an enormous range of Archival Research (AR) investigations. Requirements for the coronagraph are defined based on its status as a technology demonstration, but its expected performance will enable unprecedented observations of nearby giant exoplanets and circumstellar disks. WFIRST is currently in the Preliminary Design and Technology Completion phase (Phase B), on schedule for launch in 2025, with several of its critical components already in production.

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