Microlensing is a unique tool, capable of detecting the "cold" planets between ∼1 and 10 au from their host stars and even unbound "free-floating" planets. This regime has been poorly sampled to date ...owing to the limitations of alternative planet-finding methods, but a watershed in discoveries is anticipated in the near future thanks to the planned microlensing surveys of WFIRST-AFTA and Euclid's Extended Mission. Of the many challenges inherent in these missions, the modeling of microlensing events will be of primary importance, yet it is often time-consuming, complex, and perceived as a daunting barrier to participation in the field. The large scale of future survey data products will require thorough but efficient modeling software, but, unlike other areas of exoplanet research, microlensing currently lacks a publicly available, well-documented package to conduct this type of analysis. We present version 1.0 of the python Lightcurve Identification and Microlensing Analysis (pyLIMA). This software is written in Python and uses existing packages as much as possible to make it widely accessible. In this paper, we describe the overall architecture of the software and the core modules for modeling single-lens events. To verify the performance of this software, we use it to model both real data sets from events published in the literature and generated test data produced using pyLIMA's simulation module. The results demonstrate that pyLIMA is an efficient tool for microlensing modeling. We will expand pyLIMA to consider more complex phenomena in the following papers.
Abstract We present pyLIMASS, a novel algorithm for estimating the physical properties of the lensing system in microlensing events. The main idea of pyLIMASS is to combine all available information ...regarding the microlensing event, defined as observables , and to estimate the parameter distributions of the system, such as the lens mass and distance. The algorithm is based on isochrones for the stars model and combines the observables using a Gaussian mixture approach. After describing the mathematical formalism and its implementation, we discuss the algorithm’s performance on simulated and published events. Generally, the pyLIMASS estimations are in good agreement (i.e., within 1 σ ) with the results of the selected published events, making it an effective tool to estimate the lens properties and their distribution. The applicability of the method was tested by using a catalog of realistically simulated events that could be observed by the future Galactic Bulge Time Domain Survey of the Nancy Grace Roman Space Telescope. By solely using constraints from the Roman lightcurves and images, pyLIMASS estimates the masses of the lens of the Roman catalog with a median precision of 20% with almost no bias.
Having successfully completed its main mission, New Horizons could now become a unique observing platform for a wider range of astrophysics. In this paper, we explore the theory and practicalities of ...using the LORRI imager to observe microlensing events in the Galactic bulge. Simultaneous observations from both Earth and New Horizons could be used to measure the properties of stellar remnant lenses such as the predicted-but so far rarely detected-population of intermediate-mass black holes. While this technique cannot be applied for stellar lenses, it is possible that a single source star could be lensed by the same foreground object in two sequential microlensing events, and we explore the opportunities that this novel strategy provides for understanding the nature of the lens. With any microlensing event, two independent mass-distance relations are required to determine the physical properties of the lens. This is most commonly achieved by combining measurements of the parallax with those of the effects of the finite extent of the source star on the event light curve. We explore whether New Horizons' trajectory could be used to constrain event parallax. As with any observatory, there are practical considerations that shape viable observing strategies.
A few observational methods allow the measurement of the mass and distance of the lens-star for a microlensing event. A first estimate can be obtained by measuring the microlensing parallax effect ...produced by either the motion of the Earth (annual parallax) or the contemporaneous observation of the lensing event from two (or more) observatories (space or terrestrial parallax) sufficiently separated from each other. Further developing ideas originally outlined by Gould as well as Mogavero & Beaulieu, we review the possibility of measuring systematically the microlensing parallax using a telescope based on the Moon surface and other space-based observing platforms, including the upcoming WFIRST space-telescope. We first generalize the Fisher matrix formulation and present results demonstrating the advantage for each observing scenario. We conclude by outlining the limitation of the Fisher matrix analysis when submitted to a practical data modeling process. By considering a lunar-based parallax observation, we find that parameter correlations introduce a significant loss in detection efficiency of the probed lunar parallax effect.
Abstract
Galactic science encompasses a wide range of subjects in the study of the Milky Way and Magellanic Clouds, from young stellar objects to X-ray binaries. Mapping these populations, and ...exploring transient phenomena within them, are among the primary science goals of the Vera C. Rubin Observatory’s Legacy Survey of Space and Time. While early versions of the survey strategy dedicated relatively few visits to the Galactic Plane region, more recent strategies under consideration envision a higher cadence within selected regions of high scientific interest. The range of galactic science presents a challenge in evaluating which strategies deliver the highest scientific returns. Here we present metrics designed to evaluate Rubin survey strategy simulations, based on the cadence of observations they deliver within regions of interest to different topics in galactic science, using variability categories defined by timescale. We also compare the fractions of exposures obtained in each filter with those recommended for the different science goals. We find that the
baseline
_
v2.x
simulations deliver observations of the high-priority regions at sufficiently high cadence to reliably detect variability on timescales >10 days or more. Follow-up observations may be necessary to properly characterize variability, especially transients, on shorter timescales. Combining the regions of interest for all the science cases considered, we identify those areas of the Galactic Plane and Magellanic Clouds of highest priority. We recommend that these refined survey footprints be used in future simulations to explore rolling cadence scenarios, and to optimize the sequence of observations in different bandpasses.
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).
Roman
will dedicate part of its core survey program to the detection of cool exoplanets via microlensing, while
Euclid
may undertake a microlensing program as an ancillary science goal. 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 at least 30% of the events’ relative proper motions
µ
rel
and 42% of the lens magnitudes. This survey would place strong constraints on the mass and distance on thousands of microlensing events observed by
Roman
just after the first year of observation. 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 and, ultimately, obtain a direct measurement of the masses, distances, and transverse motions of FFPs. 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. The recent tentative detection of an excess of short-duration events by the OGLE survey is consistent with a scenario of up to ten Earth-mass FFPs per Galactic star. For such a scenario 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 characterization of exomoons, and find that it could lead to the detection of the first exomoon.
Abstract During the last 25 yr, hundreds of binary stars and planets have been discovered toward the Galactic bulge by microlensing surveys. Thanks to a new generation of large-sky surveys, it is now ...possible to regularly detect microlensing events across the entire sky. The OMEGA Key Projet at the Las Cumbres Observatory carries out automated follow-up observations of microlensing events alerted by these surveys with the aim of identifying and characterizing exoplanets as well as stellar remnants. In this study, we present the analysis of the binary lens event Gaia20bof. By automatically requesting additional observations, the OMEGA Key Project obtained dense time coverage of an anomaly near the peak of the event, allowing characterization of the lensing system. The observed anomaly in the lightcurve is due to a binary lens. However, several models can explain the observations. Spectroscopic observations indicate that the source is located at ≤2.0 kpc, in agreement with the parallax measurements from Gaia. While the models are currently degenerate, future observations, especially the Gaia astrometric time series as well as high-resolution imaging, will provide extra constraints to distinguish between them.
Planet population synthesis models predict an abundance of planets with semimajor axes between 1 and 10 au, yet they lie at the edge of the detection limits of most planet finding techniques. ...Discovering these planets and studying their distribution is critical to understanding the physical processes that drive planet formation. ROME/REA is a gravitational microlensing project whose main science driver is to discover exoplanets in the cold outer regions of planetary systems. To achieve this, it uses a novel approach combining a multiband survey with reactive follow-up observations, exploiting the unique capabilities of the Las Cumbres Observatory global network of robotic telescopes combined with a Target and Observation Manager system. We present the main science objectives and a technical overview of the project, including initial results.
Context. Understanding the source of systematic errors in photometry is essential for their calibration. Aims. We investigate how photometry performed on difference images can be influenced by errors ...in the photometric scale factor. Methods. We explore the equations for difference image analysis (DIA), and we derive an expression describing how errors in the difference flux, the photometric scale factor and the reference flux are propagated to the object photometry. Results. We find that the error in the photometric scale factor is important, and while a few studies have shown that it can be at a significant level, it is currently neglected by the vast majority of photometric surveys employing DIA. Conclusions. Minimising the error in the photometric scale factor, or compensating for it in a post-calibration model, is crucial for reducing the systematic errors in DIA photometry.
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