The inner region of circumstellar discs makes an extra near-infrared emission (NIR bump). Detecting and studying these NIR bumps from nearby stars have been done mostly through infrared interferometry. In this work, we study the feasibility of detecting NIR bumps for Galactic bulge stars through microlensing from observations by The Nancy Grace Roman Space Telescope (RST) survey. We first simulate microlensing light curves from source stars with discs in near-infrared. Four main conclusions can be extracted from the simulations. (i) If the lens is crossing the disc inner radius, two extra and wide peaks appear and the main peak of microlensing light curve is flattened. (ii) In microlensing events with the lens impact parameters larger than the disc inner radius, the disc can break the symmetry of light curves with respect to the time of closest approach. (iii) In caustic-crossing binary microlensing, the discs produce wide peaks right before entering and immediately after exiting from the caustic curves. (iv) The disc-induced perturbations are larger in the W149 filter than in the Z087 filter, unless the lens crosses the disc condensation radius. By performing a Monte Carlo simulation, the probabilities of detecting the disc perturbations by \wfirst~are estimated ~3 and 20 per cent in single and binary microlensing, respectively. We anticipate that RST detects around 109 disc-induced perturbations during its microlensing survey if 5 per cent of its source stars have discs.
The \textit{Nancy Grace Roman Space Telescope} (\textit{ Roman}) will provide an enormous number of microlensing light curves with much better photometric precisions than ongoing ground-based observations. Such light curves will enable us to observe high-order microlensing effects which have been previously difficult to detect. In this paper, we investigate \textit{Roman}'s potential to detect and characterize short-period planets and brown dwarfs (BDs) in source systems using the orbital motion of source stars, the so-called xallarap effect. We analytically estimate the measurement uncertaint…
The impact of the free-floating planet (FFP) mass function on the event rate for the accurate microlensing parallax determination: application to Euclid and Roman parallax observation
Astrometric microlensing probes of the isolated neutron star population with Roman
Zentrum für Astronomie der Universität Heidelberg（海德堡大学天文中心）；Space Science Institute, Lawrence Livermore National Laboratory（空间科学研究所，劳伦斯利弗莫尔国家实验室）；Georgia Institute of Technology（佐治亚理工学院）
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 ha…
Isolated Stellar-Mass BlackHoles (ISMBHs) are potentially discernible through microlensing observations. In this work, we study detecting and characterizing ISMBHs with the Roman observations. We simulate a big ensemble of these events as seen by Roman and estimate the errors in the physical parameters of the lens objects, including their masses, distances, and proper motions through calculating Fisher and Covariance matrices. Since the ~2.3-year time gap between Roman's first three observing seasons and the others may lower the efficiency of realizing microlensing events and characterizing IS…
The Nancy Grace Roman Space Telescope (Roman) will perform a Galactic Exoplanet Survey (RGES) to discover bound exoplanets with semi-major axes greater than 1 au using gravitational microlensing. Roman will even be sensitive to planetary mass objects that are not gravitationally bound to any host star. Such free-floating planetary mass objects (FFPs) will be detected as isolated microlensing events with timescales shorter than a few days. A measurement of the abundance and mass function of FFPs is a powerful diagnostic of the formation and evolution of planetary systems, as well as the physics…
An Updated SynthPop Model for Microlensing Simulations I: Model Description & Evaluation
University of California Berkeley（加州大学伯克利分校）；The Ohio State University（俄亥俄州立大学）；Louisiana State University（路易斯安那州立大学）；NASA Jet Propulsion Laboratory（美国宇航局喷气推进实验室）；Space Science Institute（空间科学研究所）；Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；Institute of Astronomy, University of Cambridge（剑桥大学天文学研究所）
The VVV microlensing search has recently surveyed the region of the Galactic plane at b=0 within -10.00 < l < 10.44 deg. in the near-infrared (IR), discovering hundreds of microlensing events. In this paper we explore the microlensing events with background sources that might be located in the far disk of the Galaxy, beyond the bulge. We discuss the possible configurations for the microlensing lenses and sources located at different places within the Galactic plane. Then we search for these events using the local red clump centroids of the VVV near-IR color-magnitude diagrams. According to the…
Uncertainty in the initial-final mass relation (IFMR) has long been a problem in understanding the final stages of massive star evolution. One of the major challenges of constraining the IFMR is the difficulty of measuring the mass of non-luminous remnant objects (i.e. neutron stars and black holes). Gravitational wave detectors have opened the possibility of finding large numbers of compact objects in other galaxies, but all in merging binary systems. Gravitational lensing experiments using astrometry and photometry are capable of finding compact objects, both isolated and in binaries, in the…
Galactic microlensing datasets now comprise in excess of $10^4$ events, and with the advent of next generation microlensing surveys that may be undertaken with facilities such as the Rubin Observatory (formerly LSST) and Roman Space Telescope (formerly WFIRST), this number will increase significantly. So too will the fraction of events with measurable higher order information such as finite source effects and lens-source relative proper motion. Analysing such data requires a more sophisticated Galactic microlens modeling approach. We present a new second-generation Manchester-Besançon Microlen…
Modeling Binary Lenses and Sources with the BAGLE Python Package
University of Maryland（马里兰大学）；NASA Goddard Space Flight Center（NASA戈达德太空飞行中心）；University of California, Berkeley（加州大学伯克利分校）；Observatories of the Carnegie Institution for Science（卡内基科学研究所天文台）
For microlenses with sufficiently low mass, the angular radius of the source star can be much larger than the angular Einstein ring radius of the lens. For such extreme finite source effect (EFSE) events, finite source effects dominate throughout the duration of the event. Here, we demonstrate and explore a continuous degeneracy between multiple parameters of such EFSE events. The first component in the degeneracy arises from the fact that the directly-observable peak change of the flux depends on both the ratio of the angular source radius to the angular Einstein ring radius and the fraction …
Black hole astrometric binaries in the Roman Galactic Bulge Time Domain Survey
Observatories of the Carnegie Institution for Science（卡内基科学研究所天文台）；Department of Astronomy, University of California, Berkeley（加州大学伯克利分校天文学系）；Department of Astronomy, California Institute of Technology（加州理工学院天文学系）；Department of Physics and Astronomy, University of Utah（犹他大学物理与天文学系）；Space Telescope Science Institute（太空望远镜科学研究所）；UCLA Department of Physics and Astronomy（加州大学洛杉矶分校物理与天文学系）；Space Science Institute（空间科学研究所）；Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）
Context. Brown dwarfs are poorly understood transition objects between stars and planets, with several competing mechanisms having been proposed for their formation. Mass measurements are generally difficult for isolated objects but also for brown dwarfs orbiting low-mass stars, which are often too faint for spectroscopic follow-up. Aims. Microlensing provides an alternative tool for the discovery and investigation of such faint systems. Here we present the analysis of the microlensing event OGLE-2019-BLG-0033/MOA-2019-BLG-035, which is due to a binary system composed of a brown dwarf orbiting…
We present K2-2016-BLG-0005Lb, a densely sampled, planetary binary caustic-crossing microlensing event found from a blind search of data gathered from Campaign 9 of the Kepler K2 mission (K2C9). K2-2016-BLG-0005Lb is the first bound microlensing exoplanet discovered from space-based data. The event has caustic entry and exit points that are resolved in the K2C9 data, enabling the lens--source relative proper motion to be measured. We have fitted a binary microlens model to the Kepler data, and to simultaneous observations from multiple ground-based surveys. Whilst the ground-based data only sp…
Galactic model plays an important role in the microlensing field, not only for analyses of individual events but also for statistics of the ensemble of events. However, the Galactic models used in the field varies, and some are unrealistically simplified. Here we tested three Galactic disc dynamic models, the first is a simple standard model that was widely used in this field, whereas the other two consider the radial dependence of the velocity dispersion, and in the last model, the asymmetric drift. We found that for a typical lens mass $M_{\rm L}=0.5M_{\odot}$, the two new dynamical models p…
We present Keck/NIRC2 adaptive optics imaging of planetary microlensing event MOA-2007-BLG-400 that resolves the lens star system from the source. We find that the MOA-2007-BLG-400L planetary system consists of a $1.71\pm 0.27 M_{\rm Jup}$ planet orbiting a $0.69\pm 0.04M_{\odot}$ K-dwarf host star at a distance of $6.89\pm 0.77\,$kpc from the Sun. So, this planetary system probably resides in the Galactic bulge. The planet-host star projected separation is only weakly constrained due to the close-wide light curve degeneracy; the 2$σ$ projected separation range is 0.6--$7.2\,$AU. This host mas…
We propose that extrasolar asteroid belts can be detected through their gravitational microlensing signatures. Asteroid belt + star lens systems create so-called "pseudo-caustics", regions in the source plane where the magnification exhibits a finite but discontinuous jump. These features allow such systems to generate distinctive signatures in the microlensing light curves for a wide range of belt configurations, with source trajectories as far as tenths of the Einstein ring radius from the centre of the lens. Sample light curves for a range of asteroid belt parameters are presented. In the n…
Four-Body Gravitational Microlensing Events Involving Both a Binary Lens and a Binary Source
Chungbuk National University（忠北国立大学）；Korea Astronomy and Space Science Institute（韩国天文学与空间科学研究院）；Astronomical Observatory, University of Warsaw（华沙大学天文台）；University of Canterbury（坎特伯雷大学）；Ohio State University（俄亥俄州立大学）；University of Science and Technology（科学技术院）
The NASA Nancy Grace Roman Space Telescope (Roman) and the Vera C. Rubin Observatory Legacy Survey of Space and Time (Rubin), will transform our view of the wide-field sky, with similar sensitivities, but complementary in wavelength, spatial resolution, and time domain coverage. Here we present findings from the AURA Roman+Rubin Synergy Working group, charged by the STScI and NOIRLab Directors to identify frontier science questions in General Astrophysics, beyond the well-covered areas of Dark Energy and Cosmology, that can be uniquely addressed with Roman and Rubin synergies in observing stra…
Two independent groups reported the discovery of an isolated dark stellar remnant in the microlensing event OGLE-2011-BLG-0462 based on photometric ground-based observations coupled with astrometric measurements taken with the Hubble Space Telescope. These two analyses yielded discrepant mass measurements, with the first group reporting that the lensing object is a black hole of 7.1 +/- 1.3 solar masses whereas the other concluded that the microlensing event was caused by either a neutron star or a low-mass black hole (1.6-4.4 solar masses). Here, we scrutinize the available photometric and as…
In this article we review the astrophysical application of gravitational microlensing. After introducing the history of gravitational lensing, we present the key equations and concept of microlensing. The most frequent microlensing events are single-lens events and historically it has been used for searching dark matter in the form of compact astrophysical halo objects in the Galactic halo. We discuss about the degeneracy problem in the parameters of lens and perturbation effects that can partially break the degeneracy between the lens parameters. The rest of paper is about the astrophysical a…
The recent discovery of gravitational waves (GWs) from stellar-mass binary black holes (BBHs) provided direct evidence of the existence of these systems. BBH lenses would have gravitational microlensing signatures that are distinct from single-lens signals. We apply Bayesian statistics to examine the distinguishability of BBH microlensing events from single-lens events under ideal observing conditions, using the photometric capabilities of the Korean Microlensing Telescope Network. Given one year of observations, a source star at the Galactic Centre, a GW150914-like BBH lens (total mass 65M$_\…
