Showing papers by "Radek Poleski published in 2018"

OGLE-2017-BLG-1434Lb: Eighth q<1×10-4 Mass-Ratio Microlens Planet Confirms Turnover in Planet Mass-Ratio Function

Abstract: We report the discovery of a cold Super-Earth planet (mp=4.4±0.5 M⊕) orbiting a low-mass (M=0.23±0.03) M⊙ dwarf at projected separation a⊥=1.18±0.10 a.u., i.e., about 1.9 times the distance the snow line. The system is quite nearby for a microlensing planet, DL=0.86±0.09 kpc. Indeed, it was the large lens-source relative parallax πrel=1.0 mas (combined with the low mass M) that gave rise to the large, and thus well-measured, "microlens parallax" πE∝(πrel/M)1/2 that enabled these precise measurements. OGLE-2017-BLG-1434Lb is the eighth microlensing planet with planet-host mass ratio q<1×10-4. We apply a new planet-detection sensitivity method, which is a variant of "V/Vmax", to seven of these eight planets to derive the mass-ratio function in this regime. We find dN/d lnq ∝ qp, with p=1.05+0.78-0.68, which confirms the "turnover" in the mass function found by Suzuki et al. relative to the power law of opposite sign n=-0.93±0.13 at higher mass ratios q≳2×10-4. We combine our result with that of Suzuki et al. to obtain p=0.73+0.42-0.34.

OGLE-2015-BLG-1459L: The Challenges of Exo-Moon Microlensing

Abstract: Work by K.H.H. was support by KASI grant 2017-1-830-03. Work by W.Z., Y.K.J., and A.G. were supported by AST-1516842 from the US NSF. W.Z., I.G.S., and A.G. were supported by JPL grant 1500811. This research has made use of the KMTNet system operated by the Korea Astronomy and Space Science Institute (KASI) and the data were obtained at three host sites of CTIO in Chile, SAAO in South Africa, and SSO in Australia. Work by C.H. was supported by the grant (2017R1A4A101517) of National Research Foundation of Korea. The OGLE Team thanks Prof. G. Pietrzynski for his contribution to the collection of the OGLE photometric data. The OGLE project has received funding from the National Science Centre, Poland, grant MAESTRO 2014/14/A/ST9/00121 to AU. The MOA project is supported by JSPS KAKENHI Grant Number JSPS24253004, JSPS26247023, JSPS23340064, JSPS15H00781, and JP16H06287.

OGLE-2017-BLG-1434Lb: Eighth q < 1 * 10^-4 Mass-Ratio Microlens Planet Confirms Turnover in Planet Mass-Ratio Function

Abstract: We report the discovery of a cold Super-Earth planet (m_p=44 +/- 05 M_Earth) orbiting a low-mass (M=023 +/- 003 M_Sun) M dwarf at projected separation a_perp = 118 +/- 010 AU, ie, about 19 times the snow line The system is quite nearby for a microlensing planet, D_Lens = 086 +/- 009 kpc Indeed, it was the large lens-source relative parallax pi_rel=10 mas (combined with the low mass M) that gave rise to the large, and thus well-measured, "microlens parallax" that enabled these precise measurements OGLE-2017-BLG-1434Lb is the eighth microlensing planet with planet-host mass ratio q < 1 * 10^-4 We apply a new planet-detection sensitivity method, which is a variant of "V/V_max", to seven of these eight planets to derive the mass-ratio function in this regime We find dN/d(ln q) ~ q^p, with p = 105 (+078,-068), which confirms the "turnover" in the mass function found by Suzuki et al relative to the power law of opposite sign n = -093 +/- 013 at higher mass ratios q >~ 2 * 10^-4 We combine our result with that of Suzuki et al to obtain p = 073 (+042,-034)

A Planetary Microlensing Event with an Unusually Red Source Star: MOA-2011-BLG-291

Abstract: We present the analysis of the planetary microlensing event MOA-2011-BLG-291, which has a mass ratio of q = (3.8 ± 0.7) × 10−4 and a source star that is redder (or brighter) than the bulge main sequence. This event is located at a low Galactic latitude in the survey area that is currently planned for NASA's Wide Field Infrared Survey Telescope (WFIRST) exoplanet microlensing survey. This unusual color for a microlensed source star implies that we cannot assume that the source star is in the Galactic bulge. The favored interpretation is that the source star is a lower main-sequence star at a distance of D_S = 4.9 ± 1.3 kpc in the Galactic disk. However, the source could also be a turn-off star on the far side of the bulge or a subgiant in the far side of the Galactic disk if it experiences significantly more reddening than the bulge red clump stars. However, these possibilities have only a small effect on our mass estimates for the host star and planet. We find host star and planet masses of M_(host) = 0.15^(+0.27)_(-0.10) M⊙ and m_p = 18^(+34)_(-12) M⊕ from a Bayesian analysis with a standard Galactic model, under the assumption that the planet hosting probability does not depend on the host mass or distance. However, if we attempt to measure the host and planet masses with host star brightness measurements from high angular resolution follow-up imaging, the implied masses will be sensitive to the host star distance. The WFIRST exoplanet microlensing survey is expected to use this method to determine the masses for many of the planetary systems that it discovers, so this issue has important design implications for the WFIRST exoplanet microlensing survey.

A Planetary Microlensing Event with an Unusually Red Source Star: MOA-2011-BLG-291

Abstract: We present the analysis of planetary microlensing event MOA-2011-BLG-291, which has a mass ratio of $q=(3.8\pm0.7)\times10^{-4}$ and a source star that is redder (or brighter) than the bulge main sequence. This event is located at a low Galactic latitude in the survey area that is currently planned for NASA's WFIRST exoplanet microlensing survey. This unusual color for a microlensed source star implies that we cannot assume that the source star is in the Galactic bulge. The favored interpretation is that the source star is a lower main sequence star at a distance of $D_S=4.9\pm1.3\,$kpc in the Galactic disk. However, the source could also be a turn-off star on the far side of the bulge or a sub-giant in the far side of the Galactic disk if it experiences significantly more reddening than the bulge red clump stars. However, these possibilities have only a small effect on our mass estimates for the host star and planet. We find host star and planet masses of $M_{\rm host} =0.15^{+0.27}_{-0.10}M_\odot$ and $m_p=18^{+34}_{-12}M_\oplus$ from a Bayesian analysis with a standard Galactic model under the assumption that the planet hosting probability does not depend on the host mass or distance. However, if we attempt to measure the host and planet masses with host star brightness measurements from high angular resolution follow-up imaging, the implied masses will be sensitive to the host star distance. The WFIRST exoplanet microlensing survey is expected to use this method to determine the masses for many of the planetary systems that it discovers, so this issue has important design implications for the WFIRST exoplanet microlensing survey.

OGLE-2017-BLG-0482Lb: A Microlensing Super-Earth Orbiting a Low-mass Host Star

Abstract: Work by C.H. was supported by the grant (2017R1A4A1015178) of National Research Foundation of Korea. The MOA project is supported by JSPS KAKENHI grant Nos. JSPS24253004, JSPS26247023, JSPS23340064, JSPS15H00781, and JP16H06287. The OGLE project has received funding from the National Science Centre, Poland, grant MAESTRO 2014/14/A/ST9/00121 to A.U. Work by A.G. was supported by JPL grant 1500811. Work by J.C.Y. was performed under contract with the California Institute of Technology (Caltech)/Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. Work by Y.S. was supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, California Institute of Technology, administered by Universities Space Research Association through a contract with NASA. We acknowledge the high-speed internet service (KREONET) provided by Korea Institute of Science and Technology Information (KISTI). This research has made use of the KMTNet system operated by the Korea Astronomy and Space Science Institute (KASI), and the data were obtained at three host sites of CTIO in Chile, SAAO in South Africa, and SSO in Australia.

OGLE-2017-BLG-0537: A Microlensing Event with a Resolvable Lens in ≲5 years from High-resolution Follow-up Observations

Abstract: We present the analysis of the binary-lens microlensing event OGLE-2017-BLG-0537. The light curve of the event exhibits two strong caustic-crossing spikes among which the second caustic crossing was resolved by high-cadence surveys. It is found that the lens components with a mass ratio ∼ 0.5 are separated in projection by ∼ 1.3θE, where θE is the angular Einstein radius. Analysis of the caustic-crossing part yields θE = 1.77± 0.16 mas and a lens-source relative proper motion of μ = 12.4± 1.1 mas yr−1. The measured μ is the third highest value among the events with measured proper motions and ∼ 3 times higher than the value of typical Galactic bulge events, making the event a strong candidate for follow-up observations to directly image the lens by separating it from the source. From the angular Einstein radius combined with the microlens parallax, it is estimated that the lens is composed of two main-sequence stars with masses M1 ∼ 0.4 M⊙ and M2 ∼ 0.2 M⊙ located at a distance of DL ∼ 1.2 kpc. However, the physical lens parameters are not very secure due to the weak microlens-parallax signal, and thus we cross check the parameters by conducting a Bayesian analysis based on the measured Einstein radius and event timescale combined with the blending constraint. From this, we find that the physical parameters estimated from the Bayesian analysis are consistent with those based on the measured microlens parallax. Resolving the lens from the source can be done in about 5 years from highresolution follow-up observations and this will provide a rare opportunity to test and refine the microlensing model. Subject headings: gravitational lensing: micro – binaries: general cheongho@astroph.chungbuk.ac.kr 001 Korea Astronomy and Space Science Institute, Daejon 34055, Republic of Korea 002 Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea 003 Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland 004 Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA 005 Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany 006 University of Canterbury, Department of Physics and Astronomy, Private Bag 4800, Christchurch 8020, New Zealand 007 Korea University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon, 34113, Republic of Korea 008 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA 009 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA 010 Physics Department and Tsinghua Centre for Astrophysics, Tsinghua University, Beijing 100084, China 011 Department of Physics, Zhejiang University, Hangzhou, 310058, China 012 Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St George Street, Toronto, ON M5S 3H8, Canada 013 School of Space Research, Kyung Hee University, Yongin, Kyeonggi 17104, Korea 014 Department of Physics & Astronomy, Seoul National University, Seoul 08826, Republic of Korea 100 KMTNet Collaboration. 101 OGLE Collaboration. 102 NASA Postdoctoral Program Fellow. 103 Corresponding author.

The WFIRST Exoplanet Microlensing Survey

Abstract: The Wide Field Infrared Survey Telescope (WFIRST) was the top ranked large space mission in the 2010 New Worlds, New Horizons decadal survey, and it was formed by merging the science programs of 3 different mission concepts, including the Microlensing Planet Finder (MPF) concept (Bennett \etal\ 2010). The WFIRST science program (Spergel \etal\ 2015) consists of a general observer program, a wavefront controlled technology program, and two targeted science programs: a program to study dark energy, and a statistical census of exoplanets with a microlensing survey, which uses nearly one quarter of WFIRST's observing time in the current design reference mission. The New Worlds, New Horizons (decadal survey) midterm assessment summarizes the science case for the WFIRST exoplanet microlensing survey with this statement: "WFIRST's microlensing census of planets beyond 1 AU will perfectly complement Kepler's census of compact systems, and WFIRST will also be able to detect free-floating planets unbound from their parent stars\rlap."

White Paper: Exoplanetary Microlensing from the Ground in the 2020s

Abstract: Microlensing can access planet populations that no other method can probe: cold wide-orbit planets beyond the snow line, planets in both the Galactic bulge and disk, and free floating planets (FFPs). The demographics of each population will provide unique constraints on planet formation. Over the past 5 years, U.S. microlensing campaigns with Spitzer and UKIRT have provided a powerful complement to international ground-based microlensing surveys, with major breakthroughs in parallax measurements and probing new regions of the Galaxy. The scientific vitality of these projects has also promoted the development of the U.S. microlensing community. In the 2020s, the U.S. can continue to play a major role in ground-based microlensing by leveraging U.S. assets to complement ongoing ground-based international surveys. LSST and UKIRT microlensing surveys would probe vast regions of the Galaxy, where planets form under drastically different conditions. Moreover, while ground-based surveys will measure the planet mass-ratio function beyond the snow line, adaptive optics (AO) observations with ELTs would turn all of these mass ratios into masses and also distinguish between very wide-orbit planets and genuine FFPs. To the extent possible, cooperation of U.S. scientists with international surveys should also be encouraged and supported.