arXiv subjects

Sebastiano Calchi Novati

Publications and source records attributed to Sebastiano Calchi Novati.

At least 37 records · Page 2Linked to original sources

arXiv2019

KMT-2018-BLG-0029Lb: A Very Low Mass-Ratio Spitzer Microlens Planet

At $q=1.81\pm 0.20 \times 10^{-5}$, KMT-2018-BLG-0029Lb has the lowest planet-host mass ratio $q$ of any microlensing planet to date by more than a factor of two. Hence, it is the first planet that probes below the apparent "pile-up" at $q=5$--10 $\times 10^{-5}$. The event was observed by {\it Spitzer}, yielding a microlens-parallax $π_{\rm E}$ measurement. Combined with a measurement of the Einstein radius $θ_{\rm E}$ from finite-source effects during the caustic crossings, these measurements imply masses of the host $M_{\rm host}=1.14^{+0.10}_{-0.12}\, M_\odot$ and planet $M_{\rm planet} = 7.59^{+0.75}_{-0.69}\,M_\oplus$, system distance $D_L = 3.38^{+0.22}_{-0.26}\,\,{\rm kpc}$ and projected separation $a_\perp = 4.27^{+0.21}_{-0.23}\,{\rm au}$. The blended light, which is substantially brighter than the microlensed source, is plausibly due to the lens and could be observed at high resolution immediately.

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arXiv2019

Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event

We report the lens mass and distance measurements of the nearby microlensing event TCP J05074264+2447555. We measure the microlens parallax vector $π_{\rm E}$ using Spitzer and ground-based light curves with constraints on the direction of lens-source relative proper motion derived from Very Large Telescope Interferometer (VLTI) GRAVITY observations. Combining this $π_{\rm E}$ determination with the angular Einstein radius $θ_{\rm E}$ measured by VLTI GRAVITY observations, we find that the lens is a star with mass $M_{\rm L} = 0.495 \pm 0.063~M_{\odot}$ at a distance $D_{\rm L} = 429 \pm 21~{\rm pc}$. We find that the blended light basically all comes from the lens. The lens-source proper motion is $μ_{\rm rel,hel} = 26.55 \pm 0.36~{\rm mas\,yr^{-1}}$, so with currently available adaptive-optics (AO) instruments, the lens and source can be resolved in 2021. This is the first microlensing event whose lens mass is unambiguously measured by interferometry + satellite parallax observations, which opens a new window for mass measurements of isolated objects such as stellar-mass black holes.

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arXiv2019

Spitzer Microlensing Program as a Probe for Globular Cluster Planets. Analysis of OGLE-2015-BLG-0448

The microlensing event OGLE-2015-BLG-0448 was observed by Spitzer and lay within the tidal radius of the globular cluster NGC 6558. The event had moderate magnification and was intensively observed, hence it had the potential to probe the distribution of planets in globular clusters. We measure the proper motion of NGC 6558 ($μ_{\rm cl}$(N,E) = (+0.36+-0.10, +1.42+-0.10) mas/yr) as well as the source and show that the lens is not a cluster member. Even though this particular event does not probe the distribution of planets in globular clusters, other potential cluster lens events can be verified using our methodology. Additionally, we find that microlens parallax measured using OGLE photometry is consistent with the value found based on the light curve displacement between Earth and Spitzer.

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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

OGLE-2017-BLG-1186: first application of asteroseismology and Gaussian processes to microlensing

We present the analysis of the event OGLE-2017-BLG-1186 from the 2017 Spitzer microlensing campaign. This is a remarkable microlensing event because its source is photometrically bright and variable, which makes it possible to perform an asteroseismic analysis using ground-based data. We find that the source star is an oscillating red giant with average timescale of $\sim 9$ d. The asteroseismic analysis also provides us source properties including the source angular size ($\sim 27~μ{\rm as}$) and distance ($\sim 11.5$ kpc), which are essential for inferring the properties of the lens. When fitting the light curve, we test the feasibility of Gaussian Processes (GPs) in handling the correlated noise caused by the variable source. We find that the parameters from the GP model are generally more loosely constrained than those from the traditional $χ^2$ minimization method. We note that this event is the first microlensing system for which asteroseismology and GPs have been used to account for the variable source. With both finite-source effect and microlens parallax measured, we find that the lens is likely a $\sim 0.045~M_{\odot}$ brown dwarf at distance $\sim 9.0$ kpc, or a $\sim 0.073~M_{\odot}$ ultracool dwarf at distance $\sim 9.8$ kpc. Combining the estimated lens properties with a Bayesian analysis using a Galactic model, we find a $\sim 35$ per cent probability for the lens to be a bulge object and $\sim 65$ per cent to be a background disc object.

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arXiv2019

OGLE-2018-BLG-1011L\lowercase{b,c}: Microlensing Planetary System with Two Giant Planets Orbiting a Low-mass Star

We report a multiplanetary system found from the analysis of microlensing event OGLE-2018-BLG-1011, for which the light curve exhibits a double-bump anomaly around the peak. We find that the anomaly cannot be fully explained by the binary-lens or binary-source interpretations and its description requires the introduction of an additional lens component. The 3L1S (3 lens components and a single source) modeling yields three sets of solutions, in which one set of solutions indicates that the lens is a planetary system in a binary, while the other two sets imply that the lens is a multiplanetary system. By investigating the fits of the individual models to the detailed light curve structure, we find that the multiple-planet solution with planet-to-host mass ratios $\sim 9.5\times 10^{-3}$ and $\sim 15\times 10^{-3}$ are favored over the other solutions. From the Bayesian analysis, we find that the lens is composed of two planets with masses $1.8^{+3..4}_{-1.1}~M_{\rm J}$ and $2.8^{+5.1}_{-1.7}~M_{\rm J}$ around a host with a mass $0.18^{+0.33}_{-0.10}~M_\odot$ and located at a distance $7.1^{+1.1}_{-1.5}~{\rm kpc}$. The estimated distance indicates that the lens is the farthest system among the known multiplanetary systems. The projected planet-host separations are $a_{\perp,2}=1.8^{+2.1}_{-1.5}~{\rm au}$ ($0.8^{+0.9}_{-0.6}~{\rm au}$) and $a_{\perp,3}=0.8^{+0.9}_{-0.6}~{\rm au}$, where the values of $a_{\perp,2}$ in and out the parenthesis are the separations corresponding to the two degenerate solutions, indicating that both planets are located beyond the snow line of the host, as with the other four multiplanetary systems previously found by microlensing.

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arXiv2019

$Spitzer$ Parallax of OGLE-2018-BLG-0596: A Low-mass-ratio Planet around an M-dwarf

We report the discovery of a $Spitzer$ microlensing planet OGLE-2018-BLG-0596Lb, with preferred planet-host mass ratio $q \sim 2\times10^{-4}$. The planetary signal, which is characterized by a short $(\sim 1~{\rm day})$ "bump" on the rising side of the lensing light curve, was densely covered by ground-based surveys. We find that the signal can be explained by a bright source that fully envelops the planetary caustic, i.e., a "Hollywood" geometry. Combined with the source proper motion measured from $Gaia$, the $Spitzer$ satellite parallax measurement makes it possible to precisely constrain the lens physical parameters. The preferred solution, in which the planet perturbs the minor image due to lensing by the host, yields a Uranus-mass planet with a mass of $M_{\rm p} = 13.9\pm1.6~M_{\oplus}$ orbiting a mid M-dwarf with a mass of $M_{\rm h} = 0.23\pm0.03~M_{\odot}$. There is also a second possible solution that is substantially disfavored but cannot be ruled out, for which the planet perturbs the major image. The latter solution yields $M_{\rm p} = 1.2\pm0.2~M_{\oplus}$ and $M_{\rm h} = 0.15\pm0.02~M_{\odot}$. By combining the microlensing and $Gaia$ data together with a Galactic model, we find in either case that the lens lies on the near side of the Galactic bulge at a distance $D_{\rm L} \sim 6\pm1~{\rm kpc}$. Future adaptive optics observations may decisively resolve the major image/minor image degeneracy.

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arXiv2019

Spitzer Microlensing parallax reveals two isolated stars in the Galactic bulge

We report the mass and distance measurements of two single-lens events from the 2017 Spitzer microlensing campaign. The ground-based observations yield the detection of finite-source effects, and the microlens parallaxes are derived from the joint analysis of ground-based observations and Spitzer observations. We find that the lens of OGLE-2017-BLG-1254 is a $0.60 \pm 0.03 M_{\odot}$ star with $D_{\rm LS} = 0.53 \pm 0.11~\text{kpc}$, where $D_{\rm LS}$ is the distance between the lens and the source. The second event, OGLE-2017-BLG-1161, is subject to the known satellite parallax degeneracy, and thus is either a $0.51^{+0.12}_{-0.10} M_{\odot}$ star with $D_{\rm LS} = 0.40 \pm 0.12~\text{kpc}$ or a $0.38^{+0.13}_{-0.12} M_{\odot}$ star with $D_{\rm LS} = 0.53 \pm 0.19~\text{kpc}$. Both of the lenses are therefore isolated stars in the Galactic bulge. By comparing the mass and distance distributions of the eight published Spitzer finite-source events with the expectations from a Galactic model, we find that the Spitzer sample is in agreement with the probability of finite-source effects occurrence in single lens events.

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arXiv2019

OGLE-2018-BLG-0022: First Prediction of an Astrometric Microlensing Signal from a Photometric Microlensing Event

In this work, we present the analysis of the binary microlensing event OGLE-2018-BLG-0022 that is detected toward the Galactic bulge field. The dense and continuous coverage with the high-quality photometry data from ground-based observations combined with the space-based {\it Spitzer} observations of this long time-scale event enables us to uniquely determine the masses $M_1=0.40 \pm 0.05~M_\odot$ and $M_2=0.13\pm 0.01~M_\odot$ of the individual lens components. Because the lens-source relative parallax and the vector lens-source relative proper motion are unambiguously determined, we can likewise unambiguously predict the astrometric offset between the light centroid of the magnified images (as observed by the {\it Gaia} satellite) and the true position of the source. This prediction can be tested when the individual-epoch {\it Gaia} astrometric measurements are released.

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arXiv2019

"Auxiliary" Science with the WFIRST Microlensing Survey

The Wide Field Infrared Survey Telescope (WFIRST) will monitor $\sim 2$ deg$^2$ toward the Galactic bulge in a wide ($\sim 1-2~μ$m) W149 filter at 15-minute cadence with exposure times of $\sim$50s for 6 seasons of 72 days each, for a total $\sim$41,000 exposures taken over $\sim$432 days, spread over the 5-year prime mission. This will be one of the deepest exposures of the sky ever taken, reaching a photon-noise photometric precision of 0.01 mag per exposure and collecting a total of $\sim 10^9$ photons over the course of the survey for a W149$_{\rm AB}\sim 21$ star. Of order $4 \times 10^7$ stars will be monitored with W149$_{\rm AB}$<21, and 10$^8$ stars with W145$_{\rm AB}$<23. The WFIRST microlensing survey will detect $\sim$54,000 microlensing events, of which roughly 1% ($\sim$500) will be due to isolated black holes, and $\sim$3% ($\sim$1600) will be due to isolated neutron stars. It will be sensitive to (effectively) isolated compact objects with masses as low as the mass of Pluto, thereby enabling a measurement of the compact object mass function over 10 orders of magnitude. Assuming photon-noise limited precision, it will detect $\sim 10^5$ transiting planets with sizes as small as $\sim 2~R_\oplus$, perform asteroseismology of $\sim 10^6$ giant stars, measure the proper motions to $\sim 0.3\%$ and parallaxes to $\sim 10\%$ for the $\sim 6 \times 10^6$ disk and bulge stars in the survey area, and directly detect $\sim 5 \times 10^3$ Trans-Neptunian objects (TNOs) with diameters down to $\sim 10$ km, as well as detect $\sim 10^3$ occulations of stars by TNOs during the survey. All of this science will completely serendipitous, i.e., it will not require modifications of the WFIRST optimal microlensing survey design. Allowing for some minor deviation from the optimal design, such as monitoring the Galactic center, would enable an even broader range of transformational science.

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arXiv2019

Measurement of the Free-Floating Planet Mass Function with Simultaneous Euclid and WFIRST Microlensing Parallax Observations

Free-floating planets are the remnants of violent dynamical rearrangements of planetary systems. It is possible that even our own solar system ejected a large planet early in its evolution. WFIRST will have the ability to detect free-floating planets over a wide range of masses, but it will not be able to directly measure their masses. Microlensing parallax observations can be used to measure the masses of isolated objects, including free-floating planets, by observing their microlensing events from two locations. The intra-L2 separation between WFIRST and Euclid is large enough to enable microlensing parallax measurements, especially given the exquisite photometric precision that both spacecraft are capable of over wide fields. In this white paper we describe how a modest investment of observing time could yield hundreds of parallax measurements for WFIRST's bound and free-floating planets. We also describe how a short observing campaign of precursor observations by Euclid can improve WFIRST's bound planet and host star mass measurements.

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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

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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arXiv2019

Spitzer Microlensing of MOA-2016-BLG-231L : A Counter-Rotating Brown Dwarf Binary in the Galactic Disk

We analyze the binary microlensing event MOA-2016-BLG-231, which was observed from the ground and from Spitzer. The lens is composed of very low-mass brown dwarfs (BDs) with $M_1 = 21^{+12}_{-5} \ M_J$ and $M_2 = 9^{+5}_{-2}\ M_J$, and it is located in the Galactic disk $D_{\rm L} = 2.85^{+0.88}_{-0.50}\ {\rm kpc}$. This is the fifth binary brown dwarf discovered by microlensing, and the BD binary is moving counter to the orbital motion of disk stars. Constraints on the lens physical properties come from late time, non-caustic-crossing features of the Spitzer light curve. Thus, MOA-2016-BLG-231 shows how Spitzer plays a crucial role in resolving the nature of BDs in binary BD events with short timescale ($\lesssim 10$ days).

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arXiv2019

$Spitzer$ Microlensing Parallax for OGLE-2017-BLG-0896 Reveals a Counter-Rotating Low-Mass Brown Dwarf

The kinematics of isolated brown dwarfs in the Galaxy, beyond the solar neighborhood, is virtually unknown. Microlensing has the potential to probe this hidden population, as it can measure both the mass and five of the six phase-space coordinates (all except the radial velocity) even of a dark isolated lens. However, the measurements of both the microlens parallax and finite-source effects are needed in order to recover the full information. Here, we combine $Spitzer$ satellite parallax measurement with the ground-based light curve, which exhibits strong finite-source effects, of event OGLE-2017-BLG-0896. We find two degenerate solutions for the lens (due to the known satellite-parallax degeneracy), which are consistent with each other except for their proper motion. The lens is an isolated brown dwarf with a mass of either $18\pm1M_J$ or $20\pm1M_J$. This is the lowest isolated-object mass measurement to date, only $\sim$45\% more massive than the theoretical deuterium-fusion boundary at solar metallicity, which is the common definition of a free-floating planet. The brown dwarf is located at either $3.9\pm0.1$ kpc or $4.1\pm0.1$ kpc toward the Galactic bulge, but with proper motion in the opposite direction of disk stars, with one solution suggesting it is moving within the Galactic plane. While it is possibly a halo brown dwarf, it might also represent a different, unknown population.

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arXiv2019

Key Technologies for the Wide Field Infrared Survey Telescope Coronagraph Instrument

The Wide Field Infrared Survey Telescope (WFIRST) Coronagraph Instrument (CGI) is a high-contrast imager and integral field spectrograph that will enable the study of exoplanets and circumstellar disks at visible wavelengths. Ground-based high-contrast instrumentation has fundamentally limited performance at small working angles, even under optimistic assumptions for 30m-class telescopes. There is a strong scientific driver for better performance, particularly at visible wavelengths. Future flagship mission concepts aim to image Earth analogues with visible light flux ratios of more than 10^10. CGI is a critical intermediate step toward that goal, with a predicted 10^8-9 flux ratio capability in the visible. CGI achieves this through improvements over current ground and space systems in several areas: (i) Hardware: space-qualified (TRL9) deformable mirrors, detectors, and coronagraphs, (ii) Algorithms: wavefront sensing and control; post-processing of integral field spectrograph, polarimetric, and extended object data, and (iii) Validation of telescope and instrument models at high accuracy and precision. This white paper, submitted to the 2018 NAS Exoplanet Science Strategy call, describes the status of key CGI technologies and presents ways in which performance is likely to evolve as the CGI design matures.

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arXiv2018

The KELT Follow-Up Network and Transit False Positive Catalog: Pre-vetted False Positives for TESS

The Kilodegree Extremely Little Telescope (KELT) project has been conducting a photometric survey for transiting planets orbiting bright stars for over ten years. The KELT images have a pixel scale of ~23"/pixel---very similar to that of NASA's Transiting Exoplanet Survey Satellite (TESS)---as well as a large point spread function, and the KELT reduction pipeline uses a weighted photometric aperture with radius 3'. At this angular scale, multiple stars are typically blended in the photometric apertures. In order to identify false positives and confirm transiting exoplanets, we have assembled a follow-up network (KELT-FUN) to conduct imaging with higher spatial resolution, cadence, and photometric precision than the KELT telescopes, as well as spectroscopic observations of the candidate host stars. The KELT-FUN team has followed-up over 1,600 planet candidates since 2011, resulting in more than 20 planet discoveries. Excluding ~450 false alarms of non-astrophysical origin (i.e., instrumental noise or systematics), we present an all-sky catalog of the 1,128 bright stars (6<V<10) that show transit-like features in the KELT light curves, but which were subsequently determined to be astrophysical false positives (FPs) after photometric and/or spectroscopic follow-up observations. The KELT-FUN team continues to pursue KELT and other planet candidates and will eventually follow up certain classes of TESS candidates. The KELT FP catalog will help minimize the duplication of follow-up observations by current and future transit surveys such as TESS.

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