Browsing by Author "Bachelet E"

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    An analysis of binary microlensing event OGLE-2015-BLG-0060
    (Oxford University Press on behalf of the Royal Astronomical Society, 2019-08) Tsapras Y; Cassan A; Ranc C; Bachelet E; Street R; Udalski A; Hundertmark M; Bozza V; Beaulieu JP; Marquette JB; Euteneuer E; Bramich DM; Dominik M; Figuera Jaimes R; Horne K; Mao S; Menzies J; Schmidt R; Snodgrass C; Steele IA; Wambsganss J; Mróz P; Szymański MK; Soszyński I; Skowron J; Pietrukowicz P; Kozłowski S; Poleski R; Ulaczyk K; Pawlak M; Jørgensen UG; Skottfelt J; Popovas A; Ciceri S; Korhonen H; Kuffmeier M; Evans DF; Peixinho N; Hinse TC; Burgdorf MJ; Southworth J; Tronsgaard R; Kerins E; Andersen MI; Rahvar S; Wang Y; Wertz O; Rabus M; Calchi Novati S; D'Ago G; Scarpetta G; Mancini L; Abe F; Asakura Y; Bennett DP; Bhattacharya A; Donachie M; Evans P; Fukui A; Hirao Y; Itow Y; Kawasaki K; Koshimoto N; Li MCA; Ling CH; Masuda K; Matsubara Y; Muraki Y; Miyazaki S; Nagakane M; Ohnishi K; Rattenbury N; Saito T; Sharan A; Shibai H; Sullivan DJ; Sumi T; Suzuki D; Tristram PJ; Yamada T; Yonehara A; The RoboNet team; The OGLE collaboration; The MiNDSTEp collaboration; The MOA collaboration
    We present the analysis of stellar binary microlensing event OGLE-2015-BLG-0060 based on observations obtained from 13 different telescopes. Intensive coverage of the anomalous parts of the light curve was achieved by automated follow-up observations from the robotic telescopes of the Las Cumbres Observatory. We show that, for the first time, all main features of an anomalous microlensing event are well covered by follow-up data, allowing us to estimate the physical parameters of the lens. The strong detection of second-order effects in the event light curve necessitates the inclusion of longer-baseline survey data in order to constrain the parallax vector. We find that the event was most likely caused by a stellar binary-lens with masses M = 0.87 pm 0.12 mathrm{M} and M = 0.77 pm 0.11 mathrm{M}. The distance to the lensing system is 6.41 ± 0.14 kpc and the projected separation between the two components is 13.85 ± 0.16 au. Alternative interpretations are also considered.
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    An Isolated Stellar-mass Black Hole Detected through Astrometric Microlensing
    (IOP Publishing on behalf of the American Astronomical Society, 2022-07-06) Sahu KC; Anderson J; Casertano S; Bond HE; Udalski A; Dominik M; Calamida A; Bellini A; Brown TM; Rejkuba M; Bajaj V; Kains N; Ferguson HC; Fryer CL; Yock P; Mróz P; Kozłowski S; Pietrukowicz P; Poleski R; Skowron J; Soszyński I; Szymański MK; Ulaczyk K; Wyrzykowski Ł; Barry RK; Bennett DP; Bond IA; Hirao Y; Silva SI; Kondo I; Koshimoto N; Ranc C; Rattenbury NJ; Sumi T; Suzuki D; Tristram PJ; Vandorou A; Beaulieu J-P; Marquette J-B; Cole A; Fouqué P; Hill K; Dieters S; Coutures C; Dominis-Prester D; Bennett C; Bachelet E; Menzies J; Albrow M; Pollard K; Gould A; Yee JC; Allen W; Almeida LA; Christie G; Drummond J; Gal-Yam A; Gorbikov E; Jablonski F; Lee C-U; Maoz D; Manulis I; McCormick J; Natusch T; Pogge RW; Shvartzvald Y; Jørgensen UG; Alsubai KA; Andersen MI; Bozza V; Novati SC; Burgdorf M; Hinse TC; Hundertmark M; Husser T-O; Kerins E; Longa-Peña P; Mancini L; Penny M; Rahvar S; Ricci D; Sajadian S; Skottfelt J; Snodgrass C; Southworth J; Tregloan-Reed J; Wambsganss J; Wertz O; Tsapras Y; Street RA; Bramich DM; Horne K; Steele IA
    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 6 yr, 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 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 M ⊙ 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 �1/445 km s-1, 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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    Four microlensing giant planets detected through signals produced by minor-image perturbations
    (EDP Sciences on behalf of The European Southern Observatory, 2024-07) Han C; Bond IA; Lee C-U; Gould A; Albrow MD; Chung S-J; Hwang K-H; Jung YK; Ryu Y-H; Shvartzvald Y; Shin I-G; Yee JC; Yang H; Zang W; Cha S-M; Kim D; Kim D-J; Kim S-L; Lee D-J; Lee Y; Park B-G; Pogge RW; Abe F; Bando K; Barry R; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Hamada R; Hamada S; Hamasaki N; Hirao Y; Silva SI; Itow Y; Kirikawa R; Koshimoto N; Matsubara Y; Miyazaki S; Muraki Y; Nagai T; Nunota K; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Sumi T; Suzuki D; Tomoyoshi M; Tristram PJ; Vandorou A; Yama H; Yamashita K; Bachelet E; Rota P; Bozza V; Zielinski P; Street RA; Tsapras Y; Hundertmark M; Wambsganss J; Wyrzykowski Ł; Jaimes RF; Cassan A; Dominik M; Rybicki KA; Rabus M
    Aims. We investigated the nature of the anomalies appearing in four microlensing events KMT-2020-BLG-0757, KMT-2022-BLG-0732, KMT-2022-BLG-1787, and KMT-2022-BLG-1852. The light curves of these events commonly exhibit initial bumps followed by subsequent troughs that extend across a substantial portion of the light curves. Methods. We performed thorough modeling of the anomalies to elucidate their characteristics. Despite their prolonged durations, which differ from the usual brief anomalies observed in typical planetary events, our analysis revealed that each anomaly in these events originated from a planetary companion located within the Einstein ring of the primary star. It was found that the initial bump arouse when the source star crossed one of the planetary caustics, while the subsequent trough feature occurred as the source traversed the region of minor image perturbations lying between the pair of planetary caustics. Results. The estimated masses of the host and planet, their mass ratios, and the distance to the discovered planetary systems are (Mhost/M☉, Mplanet/MJ, q/10−3, DL/kpc) = (0.58−+00.3033, 10.71−+56.6117, 17.61 ± 2.25, 6.67+−01.9330) for KMT-2020-BLG-0757, (0.53+−00.3131, 1.12+−00.6565, 2.01 ± 0.07, 6.66+−11.1984) for KMT-2022-BLG-0732, (0.42−+00.2332, 6.64−+43.9864, 15.07 ± 0.86, 7.55+−01.8930) for KMT-2022-BLG-1787, and (0.32+−00.3419, 4.98+−52.4294, 8.74 ± 0.49, 6.27+−01.9015) for KMT-2022-BLG-1852. These parameters indicate that all the planets are giants with masses exceeding the mass of Jupiter in our solar system and the hosts are low-mass stars with masses substantially less massive than the Sun.
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    MOA-2020-BLG-208Lb: Cool Sub-Saturn-mass Planet within Predicted Desert
    (American Astronomical Society, 2023-03) Olmschenk G; Bennett DP; Bond IA; Zang W; Jung YK; Yee JC; Bachelet E; Abe F; Barry RK; Bhattacharya A; Fujii H; Fukui A; Hirao Y; Silva SI; Itow Y; Kirikawa R; Kondo I; Koshimoto N; Matsubara Y; Matsumoto S; Miyazaki S; Munford B; Muraki Y; Okamura A; Ranc C; Rattenbury NJ; Satoh Y; Sumi T; Suzuki D; Toda T; Tristram PJ; Vandorou A; Yama H; Albrow MD; Cha S-M; Chung S-J; Gould A; Han C; Hwang K-H; Kim D-J; Kim H-W; Kim S-L; Lee C-U; Lee D-J; Lee Y; Park B-G; Pogge RW; Ryu Y-H; Shin I-G; Shvartzvald Y; Christie G; Cooper T; Drummond J; Green J; Hennerley S; McCormick J; Monard LAG; Natusch T; Porritt I; Tan T-G; Mao S; Maoz D; Penny MT; Zhu W; Bozza V; Cassan A; Dominik M; Hundertmark M; Jaimes RF; Kruszyńska K; Rybicki KA; Street RA; Tsapras Y; Wambsganss J; Wyrzykowski L; Zieliński P; Rau G
    We analyze the MOA-2020-BLG-208 gravitational microlensing event and present the discovery and characterization of a new planet, MOA-2020-BLG-208Lb, with an estimated sub-Saturn mass. With a mass ratio q=3.17-0.26+0.28×10-4, the planet lies near the peak of the mass-ratio function derived by the MOA collaboration and near the edge of expected sample sensitivity. For these estimates we provide results using two mass-law priors: one assuming that all stars have an equal planet-hosting probability, and the other assuming that planets are more likely to orbit around more massive stars. In the first scenario, we estimate that the lens system is likely to be a planet of mass mplanet=46-24+42M⊕ and a host star of mass Mhost=0.43-0.23+0.39M⊙, located at a distance DL=7.49-1.13+0.99kpc . For the second scenario, we estimate mplanet=69-34+37M⊕, Mhost=0.66-0.32+0.35M⊙, and DL=7.81-0.93+0.93kpc . The planet has a projected separation as a fraction of the Einstein ring radius s=1.3807-0.0018+0.0018 . As a cool sub-Saturn-mass planet, this planet adds to a growing collection of evidence for revised planetary formation models
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    Unveiling MOA-2007-BLG-192: An M Dwarf Hosting a Likely Super-Earth
    (American Astronomical Society, 2024-07-15) Terry SK; Beaulieu J-P; Bennett DP; Hamdorf E; Bhattacharya A; Chaudhry V; Cole AA; Koshimoto N; Anderson J; Bachelet E; Blackman JW; Bond IA; Lu JR; Marquette JB; Ranc C; Rektsini NE; Sahu K; Vandorou A
    We present an analysis of high-angular-resolution images of the microlensing target MOA-2007-BLG-192 using Keck adaptive optics and the Hubble Space Telescope. The planetary host star is robustly detected as it separates from the background source star in nearly all of the Keck and Hubble data. The amplitude and direction of the lens-source separation allows us to break a degeneracy related to the microlensing parallax and source radius crossing time. Thus, we are able to reduce the number of possible binary-lens solutions by a factor of ∼2, demonstrating the power of high-angular-resolution follow-up imaging for events with sparse light-curve coverage. Following Bennett et al., we apply constraints from the high-resolution imaging on the light-curve modeling to find host star and planet masses of M host = 0.28 ± 0.04 M ☉ and m p = 12.49 − 8.03 + 65.47 M ⊕ at a distance from Earth of D L = 2.16 ± 0.30 kpc. This work illustrates the necessity for the Nancy Grace Roman Galactic Exoplanet Survey to use its own high-resolution imaging to inform light-curve modeling for microlensing planets that the mission discovers.