Showing papers by "M. Kubiak published in 2009"
TL;DR: In this article, a fast method for modeling and classifying non-periodic continuously varying sources (quasars, aperiodic stellar variability) is presented. But this method is limited to the case of the OGLE-II survey of the LMC.
Abstract: Robust fast methods to classify variable light curves in large sky surveys are becoming increasingly important. While it is relatively straightforward to identify common periodic stars and particular transient events (supernovae, novae, microlensing), there is no equivalent for non-periodic continuously varying sources (quasars, aperiodic stellar variability). In this paper we present a fast method for modeling and classifying such sources. We demonstrate the method using ~ 86,000 variable sources from the OGLE-II survey of the LMC and ~ 2,700 mid-IR selected quasar candidates from the OGLE-III survey of the LMC and SMC. We discuss the location of common variability classes in the parameter space of the model. In particular we show that quasars occupy a distinct region of variability space, providing a simple quantitative approach to the variability selection of quasars.
304 citations
TL;DR: A Neptune-mass planet OGLE-2007-BLG-368Lb with a planet-star mass ratio of q=[9.5 +/- 2.1] x 10^{-5} via gravitational microlensing was discovered in real-time thanks to the high cadence of the MOA survey and intensive follow-up observations as mentioned in this paper.
Abstract: We present the discovery of a Neptune-mass planet OGLE-2007-BLG-368Lb with a planet-star mass ratio of q=[9.5 +/- 2.1] x 10^{-5} via gravitational microlensing. The planetary deviation was detected in real-time thanks to the high cadence of the MOA survey, real-time light curve monitoring and intensive follow-up observations. A Bayesian analysis returns the stellar mass and distance at M_l = 0.64_{-0.26}^{+0.21} M_\sun and D_l = 5.9_{-1.4}^{+0.9} kpc, respectively, so the mass and separation of the planet are M_p = 20_{-8}^{+7} M_\oplus and a = 3.3_{-0.8}^{+1.4} AU, respectively. This discovery adds another cold Neptune-mass planet to the planetary sample discovered by microlensing, which now comprise four cold Neptune/Super-Earths, five gas giant planets, and another sub-Saturn mass planet whose nature is unclear. The discovery of these ten cold exoplanets by the microlensing method implies that the mass ratio function of cold exoplanets scales as dN_{\rm pl}/d\log q \propto q^{-0.7 +/- 0.2} with a 95% confidence level upper limit of n < -0.35 (where dN_{\rm pl}/d\log q \propto q^n). As microlensing is most sensitive to planets beyond the snow-line, this implies that Neptune-mass planets are at least three times more common than Jupiters in this region at the 95% confidence level.
217 citations
Ohio State University1, University of Warsaw2, Space Telescope Science Institute3, University of Concepción4, University of Cambridge5, Pennsylvania State University6, Weizmann Institute of Science7, Chungbuk National University8, American Museum of Natural History9, California Institute of Technology10, Korea Astronomy and Space Science Institute11, Nagoya University12, University of Notre Dame13, Massey University14, University of Canterbury15, Victoria University of Wellington16, Konan University17, University of Manchester18, College of Industrial Technology19, Japan Aerospace Exploration Agency20, University of Auckland21, Institut d'Astrophysique de Paris22, European Southern Observatory23, University of the Free State24, Heidelberg University25, Lawrence Livermore National Laboratory26, University of Tasmania27, University of Rijeka28, University of Vienna29, University of Toulouse30, University of St Andrews31, Niels Bohr Institute32, Liverpool John Moores University33, University of Grenoble34
TL;DR: The OGLE-2005-BLG-071Lb was discovered by microlensing and the first in a high-magnification event as discussed by the authors, and the second largest known planet.
Abstract: We combine all available information to constrain the nature of OGLE-2005-BLG-071Lb, the second planet discovered by microlensing and the first in a high-magnification event. These include photometric and astrometric measurements from the Hubble Space Telescope, as well as constraints from higher order effects extracted from the ground-based light curve, such as microlens parallax, planetary orbital motion, and finite-source effects. Our primary analysis leads to the conclusion that the host of Jovian planet OGLE-2005-BLG-071Lb is an M dwarf in the foreground disk with mass M = 0.46 ± 0.04 Msun, distance Dl = 3.2 ± 0.4 kpc, and thick-disk kinematics vLSR ~ 103 km s‑1. From the best-fit model, the planet has mass Mp = 3.8 ± 0.4 MJupiter, lies at a projected separation r⊥ = 3.6 ± 0.2AU from its host, and so has an equilibrium temperature of T ~ 55 K, that is, similar to Neptune. A degenerate model gives similar planetary mass Mp = 3.4 ± 0.4 MJupiter with a smaller projected separation, r⊥ = 2.1 ± 0.1AU, and higher equilibrium temperature, T ~ 71 K. These results from the primary analysis suggest that OGLE-2005-BLG-071Lb is likely to be the most massive planet yet discovered that is hosted by an M dwarf. However, the formation of such high-mass planetary companions in the outer regions of M dwarf planetary systems is predicted to be unlikely within the core-accretion scenario. There are a number of caveats to this primary analysis, which assumes (based on real but limited evidence) that the unlensed light coincident with the source is actually due to the lens, that is, the planetary host. However, these caveats could mostly be resolved by a single astrometric measurement a few years after the event.
209 citations
Ohio State University1, Massey University2, Nagoya University3, University of Notre Dame4, University of Canterbury5, Victoria University of Wellington6, Konan University7, University of Auckland8, University of Manchester9, College of Industrial Technology10, Chungbuk National University11, Korea Astronomy and Space Science Institute12, Auckland University of Technology13, University of Warsaw14, University of Concepción15, University of Cambridge16
TL;DR: In this article, the authors reported the detection of the cool, Jovian-mass planet MOA-2007-BLG-400Lb in a high-magnification microlensing event.
Abstract: We report the detection of the cool, Jovian-mass planet MOA-2007-BLG-400Lb. The planet was detected in a high-magnification microlensing event (with peak magnification A max = 628) in which the primary lens transited the source, resulting in a dramatic smoothing of the peak of the event. The angular extent of the region of perturbation due to the planet is significantly smaller than the angular size of the source, and as a result the planetary signature is also smoothed out by the finite source size. Thus, the deviation from a single-lens fit is broad and relatively weak (approximately few percent). Nevertheless, we demonstrate that the planetary nature of the deviation can be unambiguously ascertained from the gross features of the residuals, and detailed analysis yields a fairly precise planet/star mass ratio of , in accord with the large significance () of the detection. The planet/star projected separation is subject to a strong close/wide degeneracy, leading to two indistinguishable solutions that differ in separation by a factor of ~8.5. Upper limits on flux from the lens constrain its mass to be M < 0.75 M ? (assuming that it is a main-sequence star). A Bayesian analysis that includes all available observational constraints indicates a primary in the Galactic bulge with a mass of ~0.2-0.5 M ? and thus a planet mass of ~0.5-1.3 M Jup. The separation and equilibrium temperature are ~5.3-9.7 AU (~0.6-1.1 AU) and ~34 K (~103 K) for the wide (close) solution. If the primary is a main-sequence star, follow-up observations would enable the detection of its light and so a measurement of its mass and distance.
168 citations
University of Warsaw1, University of St Andrews2, Ohio State University3, Nagoya University4, Space Telescope Science Institute5, University of Notre Dame6, University of Cambridge7, University of Concepción8, Texas A&M University9, Chungbuk National University10, Korea Astronomy and Space Science Institute11, Auckland University of Technology12, University of Exeter13, Astrophysics Research Institute14, University of Stuttgart15, Royal Society16, Liverpool John Moores University17, University of Manchester18, European Southern Observatory19, Las Cumbres Observatory Global Telescope Network20, Massey University21, University of Auckland22, University of Canterbury23, Victoria University of Wellington24, Konan University25, College of Industrial Technology26, Institut d'Astrophysique de Paris27, University of the Free State28, University of Toulouse29
TL;DR: The OGLE-2007-BLG-224 microlensing event was observed in this article, from which the lens is a brown dwarf of mass M = 0.056 ± 0.004 M ☉, with a distance of 525 ± 40 pc and a transverse velocity of 113 ± 21 km s−1.
Abstract: Parallax is the most fundamental technique for measuring distances to astronomical objects. Although terrestrial parallax was pioneered over 2000 years ago by Hipparchus (ca. 140 B.C.E.) to measure the distance to the Moon, the baseline of the Earth is so small that terrestrial parallax can generally only be applied to objects in the Solar System. However, there exists a class of extreme gravitational microlensing events in which the effects of terrestrial parallax can be readily detected and so permit the measurement of the distance, mass, and transverse velocity of the lens. Here we report observations of the first such extreme microlensing event OGLE-2007-BLG-224, from which we infer that the lens is a brown dwarf of mass M = 0.056 ± 0.004 M ☉, with a distance of 525 ± 40 pc and a transverse velocity of 113 ± 21 km s–1. The velocity places the lens in the thick disk, making this the lowest-mass thick-disk brown dwarf detected so far. Follow-up observations may allow one to observe the light from the brown dwarf itself, thus serving as an important constraint for evolutionary models of these objects and potentially opening a new window on substellar objects. The low a priori probability of detecting a thick-disk brown dwarf in this event, when combined with additional evidence from other observations, suggests that old substellar objects may be more common than previously assumed.
151 citations
TL;DR: The OGLE-2006-BLG-109Lb,c was the first double planet system discovered with the gravitational microlensing method as discussed by the authors, which was the only multi-planet system discovered by any method with measured masses for the star and both planets.
Abstract: We present a new analysis of the Jupiter+Saturn analog system, OGLE-2006-BLG-109Lb,c, which was the first double planet system discovered with the gravitational microlensing method. This is the only multi-planet system discovered by any method with measured masses for the star and both planets. In addition to the signatures of two planets, this event also exhibits a microlensing parallax signature and finite source effects that provide a direct measure of the masses of the star and planets, and the expected brightness of the host star is confirmed by Keck AO imaging, yielding masses of M_* = 0.51(+0.05-0.04) M_sun, M_b = 231+-19 M_earth, M_c = 86+-7 M_earth. The Saturn-analog planet in this system had a planetary light curve deviation that lasted for 11 days, and as a result, the effects of the orbital motion are visible in the microlensing light curve. We find that four of the six orbital parameters are tightly constrained and that a fifth parameter, the orbital acceleration, is weakly constrained. No orbital information is available for the Jupiter-analog planet, but its presence helps to constrain the orbital motion of the Saturn-analog planet. Assuming co-planar orbits, we find an orbital eccentricity of eccentricity = 0.15 (+0.17-0.10) and an orbital inclination of i = 64 (+4-7) deg. The 95% confidence level lower limit on the inclination of i > 49 deg. implies that this planetary system can be detected and studied via radial velocity measurements using a telescope of >30m aperture.
146 citations
TL;DR: The results from the OGLE-II survey (1996-2000) towards the Large Magellanic Cloud (LMC), which has the aim of detecting the microlensing phenomena caused by dark matter compact objects in the Galactic Halo (Machos), are presented in this paper.
Abstract: We present the results from the OGLE-II survey (1996-2000) towards the Large Magellanic Cloud (LMC), which has the aim of detecting the microlensing phenomena caused by dark matter compact objects in the Galactic Halo (Machos).
We use high resolution HST images of the OGLE fields and derive the correction for the number of monitored stars in each field. This also yield blending distributions which we use in 'catalogue level' Monte Carlo simulations of the microlensing events in order to calculate the detection efficiency of the events.
We detect two candidates for microlensing events in the All Stars Sample, which translates into an optical depth of 0.43+-0.33x 10e-7. If both events were due to Macho the fraction of mass of compact dark matter objects in the Galactic halo would be 8+-6 per cent. This optical depth, however, along with the characteristics of the events, seems to be consistent with the self-lensing scenario, i.e., self-lensing alone is sufficient to explain the observed microlensing signal. Our results indicate a non-detection of Machos lensing towards the LMC with an upper limit on their abundance in the Galactic halo of 19 per cent for M=0.4 Msun and 10 per cent for masses between 0.01 and 0.2 Msun.
93 citations
Ohio State University1, University of Warsaw2, Nagoya University3, University of Tasmania4, Tel Aviv University5, University of Concepción6, University of Cambridge7, Texas A&M University8, Institut d'Astrophysique de Paris9, Chungbuk National University10, Korea Astronomy and Space Science Institute11, Auckland University of Technology12, Massey University13, University of Canterbury14, Victoria University of Wellington15, Konan University16, University of Auckland17, Vaughn College of Aeronautics and Technology18, University of Toulouse19, University College London20, University of Notre Dame21, Heidelberg University22, University of St Andrews23
TL;DR: In this paper, the authors analyzed OGLE-2008-BLG-279, which peaked at a maximum magnification of A ~ 1600 on 2008 May 30, and determined the mass of the lens, Ml = 0.64? 0.10 M?, and its distance, Dl = 4.0 ǫ 0.6 kpc.
Abstract: We analyze the extreme high-magnification microlensing event OGLE-2008-BLG-279, which peaked at a maximum magnification of A ~ 1600 on 2008 May 30. The peak of this event exhibits both finite-source effects and terrestrial parallax, from which we determine the mass of the lens, Ml = 0.64 ? 0.10 M ?, and its distance, Dl = 4.0 ? 0.6 kpc. We rule out Jupiter-mass planetary companions to the lens star for projected separations in the range 0.5-20 AU. More generally, we find that this event was sensitive to planets with masses as small as with projected separations near the Einstein ring (~3 AU).
78 citations
TL;DR: In this article, the results from the Optical Gravitational Lensing Experiment II (OGLE-II) survey (1996-2000) towards the Large Magellanic Cloud (LMC), which has the aim of detecting the microlensing phenomena caused by dark matter compact objects in the Galactic halo [massive compact halo objects (MACHOs), were presented.
Abstract: We present the results from the Optical Gravitational Lensing Experiment II (OGLE-II) survey (1996–2000) towards the Large Magellanic Cloud (LMC), which has the aim of detecting the microlensing phenomena caused by dark matter compact objects in the Galactic halo [massive compact halo objects (MACHOs)].
We use high-resolution Hubble Space Telescope images of the OGLE fields and derive the correction for the number of monitored stars in each field. This also yields blending distributions which we use in ‘catalogue-level’ Monte Carlo simulations of the microlensing events in order to calculate the detection efficiency of the events.
We detect two candidates for microlensing events in the All Stars Sample, which translates into an optical depth of 0.43 ± 0.33 × 10−7. If both events were due to MACHO, the fraction of mass of compact dark matter objects in the Galactic halo would be 8 ± 6 per cent. This optical depth, however, along with the characteristics of the events seems to be consistent with the self-lensing scenario, i.e. self-lensing alone is sufficient to explain the observed microlensing signal. Our results indicate the non-detection of MACHOs lensing towards the LMC with an upper limit on their abundance in the Galactic halo of 19 per cent for M= 0.4 M⊙ and 10 per cent for masses between 0.01 and 0.2 M⊙.
78 citations
13 Mar 2009
TL;DR: The third part of the OGLE-III catalog of variable stars comprises 24906 RR Lyr stars in the Large Magellanic Cloud (LMC). This sample consists of 17693 fundamental-mode (RRab), 4958 first-overtone (RRc), 986 double-mode(RRd) and 1269 suspected second-overlapping pulsators.
Abstract: The third part of the OGLE-III Catalog of Variable Stars comprises 24906 RR Lyr stars in the Large Magellanic Cloud (LMC). This sample consists of 17693 fundamental-mode (RRab), 4958 first-overtone (RRc), 986 double-mode (RRd) and 1269 suspected second-overtone (RRe) pulsators. 66 objects are foreground Galactic RR Lyr stars. The catalog data include basic photometric and astrometric properties of these RR Lyr stars, multi-epoch VI photometry and finding charts.
We detected one new RR Lyr star with additional eclipsing variations. The spatial distribution of RR Lyr stars in the LMC is distinctly non-spherical and it is elongated in the same direction as the LMC bar. The basic statistical features of RR Lyr stars in the LMC are provided. The apparent V-band magnitudes for RRab stars have the modal value at 19.36 mag, and for overtone RR Lyr stars it is about 19.32 mag. The mean periods for RRab, RRc and RRe stars are 0.576, 0.337 and 0.270 days, respectively.
46 citations
TL;DR: In this article, a detailed analysis of OGLE 2004-BLG-482, a relatively high-magnification single-lens microlensing event which exhibits clear extended-source effects is presented.
Abstract: Aims: We present a detailed analysis of OGLE 2004-BLG-482, a relatively high-magnification single-lens microlensing event which exhibits clear extended-source effects. These events are relatively rare, but they potentially contain unique information on the stellar atmosphere properties of their source star, as shown in this study. Methods: Our dense photometric coverage of the overall light curve and a proper microlensing modelling allow us to derive measurements of the OGLE 2004-BLG-482 source star's linear limb-darkening coefficients in three bands, including standard Johnson-Cousins I and R, as well as in a broad clear filter. In particular, we discuss in detail the problems of multi-band and multi-site modelling on the expected precision of our results. We also obtained high-resolution UVES spectra as part of a ToO programme at ESO VLT from which we derive the source star's precise fundamental parameters. Results: From the high-resolution UVES spectra, we find that OGLE 2004-BLG-482's source star is a red giant of MK type a bit later than M3, with Teff = 3667 +/- 150 K, log g = 2.1 +/- 1.0 and an assumed solar metallicity. This is confirmed by an OGLE calibrated colour-magnitude diagram. We then obtain from a detailed microlensing modelling of the light curve linear limb-darkening coefficients that we compare to model-atmosphere predictions available in the literature, and find a very good agreement for the I and R bands. In addition, we perform a similar analysis using an alternative description of limb darkening based on a principal component analysis of ATLAS limb-darkening profiles, and also find a very good agreement between measurements and model predictions.
Institut d'Astrophysique de Paris1, Ohio State University2, Chungbuk National University3, University of Warsaw4, Weizmann Institute of Science5, University of Cambridge6, Tel Aviv University7, Korea Astronomy and Space Science Institute8, Columbia University9, Auckland University of Technology10, California Institute of Technology11, University of Canterbury12, University of Notre Dame13, European Southern Observatory14, Astrophysics Research Institute15, University of the Free State16, University of Tasmania17, Lawrence Livermore National Laboratory18, University of St Andrews19, University of Rijeka20, University of Vienna21, University of Toulouse22, University of Copenhagen23, NASA Exoplanet Science Institute24, Space Telescope Science Institute25, Liverpool John Moores University26, Queen Mary University of London27, Heidelberg University28, University of Concepción29, Nagoya University30, Massey University31, University of Auckland32, Konan University33, College of Industrial Technology34, Victoria University of Wellington35
TL;DR: In this article, a high magnification microlensing event (A ~ 432) whose peak occurred on 2 May, 2007, with pronounced finite-source and parallax effects was analyzed.
Abstract: We analyze OGLE-2007-BLG-050, a high magnification microlensing event (A ~ 432) whose peak occurred on 2 May, 2007, with pronounced finite-source and parallax effects. We compute planet detection efficiencies for this event in order to determine its sensitivity to the presence of planets around the lens star. Both finite-source and parallax effects permit a measurement of the angular Einstein radius \theta_E = 0.48 +/- 0.01 mas and the parallax \pi_E = 0.12 +/- 0.03, leading to an estimate of the lens mass M = 0.50 +/- 0.14 M_Sun and its distance to the observer D_L = 5.5 +/- 0.4 kpc. This is only the second determination of a reasonably precise (<30%) mass estimate for an isolated unseen object, using any method. This allows us to calculate the planetary detection efficiency in physical units (r_\perp, m_p), where r_\perp is the projected planet-star separation and m_p is the planet mass. When computing planet detection efficiency, we did not find any planetary signature and our detection efficiency results reveal significant sensitivity to Neptune-mass planets, and to a lesser extent Earth-mass planets in some configurations. Indeed, Jupiter and Neptune-mass planets are excluded with a high confidence for a large projected separation range between the planet and the lens star, respectively [0.6 - 10] and [1.4 - 4] AU, and Earth-mass planets are excluded with a 10% confidence in the lensing zone, i.e. [1.8 - 3.1] AU.
TL;DR: In this paper, a method for fitting binary-lens caustic-crossing microlensing events based on the alternative model parameterisation proposed and detailed in Cassan (2008) is presented.
Abstract: We outline a method for fitting binary-lens caustic-crossing microlensing events based on the alternative model parameterisation proposed and detailed in Cassan (2008). As an illustration of our methodology, we present an analysis of OGLE-2007-BLG-472, a double-peaked Galactic microlensing event with a source crossing the whole caustic structure in less than three days. In order to identify all possible models we conduct an extensive search of the parameter space, followed by a refinement of the parameters with a Markov Chain-Monte Carlo algorithm. We find a number of low-chi2 regions in the parameter space, which lead to several distinct competitive best models. We examine the parameters for each of them, and estimate their physical properties. We find that our fitting strategy locates several minima that are difficult to find with other modelling strategies and is therefore a more appropriate method to fit this type of events.
University of St Andrews1, Heidelberg University2, University of Canterbury3, Institut d'Astrophysique de Paris4, University of Toulouse5, University of Tasmania6, University of Warsaw7, University of Notre Dame8, University of Vienna9, European Southern Observatory10, Liverpool John Moores University11, Lawrence Livermore National Laboratory12, DSM13, University of Rijeka14, Niels Bohr Institute15, NASA Exoplanet Science Institute16, University of Manchester17, Space Telescope Science Institute18, University of Concepción19, University of Cambridge20
TL;DR: In this paper, a method for fitting binary-lens caustic-crossing microlensing events based on the alternative model parametrization proposed and detailed by Cassan is presented.
Abstract: We outline a method for fitting binary-lens caustic-crossing microlensing events based on the alternative model parametrization proposed and detailed by Cassan. As an illustration of our methodology, we present an analysis of OGLE-2007-BLG-472, a double-peaked Galactic microlensing event with a source crossing the whole caustic structure in less than three days. In order to identify all possible models we conduct an extensive search of the parameter space, followed by a refinement of the parameters with a Markov Chain Monte Carlo algorithm. We find a number of low-χ2 regions in the parameter space, which lead to several distinct competitive best models. We examine the parameters for each of them, and estimate their physical properties. We find that our fitting strategy locates several minima that are difficult to find with other modelling strategies and is therefore a more appropriate method to fit this type of event.
01 Dec 2009
Harvard University1, Space Telescope Science Institute2, Johns Hopkins University3, Princeton University4, Association of Universities for Research in Astronomy5, Lawrence Livermore National Laboratory6, McMaster University7, University of Washington8, Pontifical Catholic University of Chile9, University of Virginia10, University of Padua11, Andrés Bello National University12, Texas A&M University13, University of Pittsburgh14, Ludwig Maximilian University of Munich15, University of Cambridge16, University of Warsaw17, University of Concepción18
TL;DR: In this article, the authors reported the discovery of a supernova with the highest apparent energy output to date and concluded that it represents an extreme example of the Type IIn subclass.
Abstract: We report the discovery of a supernova (SN) with the highest apparent energy output to date and conclude that it represents an extreme example of the Type IIn subclass. The SN, which was discovered behind the Large Magellanic Cloud at z = 0.289 by the SuperMACHO microlensing survey, peaked at M_R = -21.5 mag and only declined by 2.9 mag over 4.7 years after the peak. Over this period, SN 2003ma had an integrated bolometric luminosity of 4 x 10^51 ergs, more than any other SN to date. The radiated energy is close to the limit allowed by conventional core-collapse explosions. Optical spectra reveal that SN 2003ma has persistent single-peaked intermediate-width hydrogen lines, a signature of interaction between the SN and a dense circumstellar medium. The light curves show further evidence for circumstellar interaction, including a long plateau with a shape very similar to the classic SN IIn 1988Z -- however, SN 2003ma is ten times more luminous at all epochs. The fast velocity measured for the intermediate-width H_alpha component (~6000 km/s) points towards an extremely energetic explosion (> 10^52 ergs), which imparts a faster blast-wave speed to the post-shock material and a higher luminosity from the interaction than is observed in typical SNe IIn. Mid-infrared observations of SN 2003ma suggest an infrared light echo is produced by normal interstellar dust at a distance ~0.5 pc from the SN.
Journal Article•
TL;DR: In this paper, the authors analyzed the light curves of microlensing events OGLE-2007-BLG-137/MOA-2007, BLG-091, OGLE2007-LG-355/MOG-278, and MOG-2009-LHG-419, and found that the perturbations of the events are caused by binary companions rather than planets.
Abstract: To improve the planet detection efficiency, current planetary microlensing experiments are focused on high-magnification events searching for planetary signals near the peak of lensing light curves. However, it is known that central perturbations can also be produced by binary companions and thus it is important to distinguish planetary signals from those induced by binary companions. In this paper, we analyze the light curves of microlensing events OGLE-2007-BLG-137/MOA-2007-BLG-091, OGLE-2007-BLG-355/MOA-2007-BLG-278, and MOA-2007-BLG-199/OGLE-2007-BLG-419, for all of which exhibit short-term perturbations near the peaks of the light curves. From detailed modeling of the light curves, we find that the perturbations of the events are caused by binary companions rather than planets. From a close examination of the light curves combined with the underlying physical geometry of the lens system obtained from modeling, we find that the short timescale caustic-crossing feature occurring at a low or a moderate base magnification with an additional secondary perturbation is a typical feature of binary-lens events and thus can be used for the discrimination between the binary and planetary interpretations.
Institut d'Astrophysique de Paris1, Ohio State University2, Chungbuk National University3, University of Warsaw4, Weizmann Institute of Science5, University of Cambridge6, Tel Aviv University7, Korea Astronomy and Space Science Institute8, Columbia University9, Auckland University of Technology10, California Institute of Technology11, University of Canterbury12, University of Notre Dame13, European Southern Observatory14, Astrophysics Research Institute15, University of the Free State16, University of Tasmania17, Lawrence Livermore National Laboratory18, University of St Andrews19, University of Rijeka20, University of Vienna21, University of Toulouse22, University of Copenhagen23, NASA Exoplanet Science Institute24, Space Telescope Science Institute25, Liverpool John Moores University26, Queen Mary University of London27, Heidelberg University28, University of Concepción29, Nagoya University30, Massey University31, University of Auckland32, Konan University33, College of Industrial Technology34, Victoria University of Wellington35
TL;DR: In this article, a high magnification microlensing event (A ~ 432) whose peak occurred on 2 May, 2007, with pronounced finite-source and parallax effects was analyzed.
Abstract: We analyze OGLE-2007-BLG-050, a high magnification microlensing event (A ~ 432) whose peak occurred on 2 May, 2007, with pronounced finite-source and parallax effects. We compute planet detection efficiencies for this event in order to determine its sensitivity to the presence of planets around the lens star. Both finite-source and parallax effects permit a measurement of the angular Einstein radius \theta_E = 0.48 +/- 0.01 mas and the parallax \pi_E = 0.12 +/- 0.03, leading to an estimate of the lens mass M = 0.50 +/- 0.14 M_Sun and its distance to the observer D_L = 5.5 +/- 0.4 kpc. This is only the second determination of a reasonably precise (<30%) mass estimate for an isolated unseen object, using any method. This allows us to calculate the planetary detection efficiency in physical units (r_\perp, m_p), where r_\perp is the projected planet-star separation and m_p is the planet mass. When computing planet detection efficiency, we did not find any planetary signature and our detection efficiency results reveal significant sensitivity to Neptune-mass planets, and to a lesser extent Earth-mass planets in some configurations. Indeed, Jupiter and Neptune-mass planets are excluded with a high confidence for a large projected separation range between the planet and the lens star, respectively [0.6 - 10] and [1.4 - 4] AU, and Earth-mass planets are excluded with a 10% confidence in the lensing zone, i.e. [1.8 - 3.1] AU.
TL;DR: In this paper, the authors analyzed the light curves of microlensing events OGLE-2007-BLG-137/MOA-2007, BLG-091, OGLE2007-LG-355/MOG-278, and MOG-2009-LHG-419, and found that the perturbations of the events are caused by binary companions rather than planets.
Abstract: To improve the planet detection efficiency, current planetary microlensing experiments are focused on high-magnification events searching for planetary signals near the peak of lensing light curves. However, it is known that central perturbations can also be produced by binary companions and thus it is important to distinguish planetary signals from those induced by binary companions. In this paper, we analyze the light curves of microlensing events OGLE-2007-BLG-137/MOA-2007-BLG-091, OGLE-2007-BLG-355/MOA-2007-BLG-278, and MOA-2007-BLG-199/OGLE-2007-BLG-419, for all of which exhibit short-term perturbations near the peaks of the light curves. From detailed modeling of the light curves, we find that the perturbations of the events are caused by binary companions rather than planets. From close examination of the light curves combined with the underlying physical geometry of the lens system obtained from modeling, we find that the short time-scale caustic-crossing feature occurring at a low or a moderate base magnification with an additional secondary perturbation is a typical feature of binary-lens events and thus can be used for the discrimination between the binary and planetary interpretations.
Posted Content•
TL;DR: The OGLE-III catalog of variable stars as discussed by the authors contains 91 995 long-period variables (LPVs) in the Large Magellanic Cloud (LMC) and the catalog data include basic photometric and astrometric properties, long-term multi-epoch VI photometry and finding charts.
Abstract: The fourth part of the OGLE-III Catalog of Variable Stars presents 91 995 long-period variables (LPVs) in the Large Magellanic Cloud (LMC). This sample consists of 79 200 OGLE Small Amplitude Red Giants (OSARGs), 11 128 semiregular variables (SRVs) and 1667 Mira stars. The catalog data include basic photometric and astrometric properties of these stars, long-term multi-epoch VI photometry and finding charts.
We describe the methods used for the identification and classification of LPVs. The distribution of I-band amplitudes for carbon-rich stars shows two maxima, corresponding to Miras and SRVs. Such a distinction between Miras and SRVs is not obvious for oxygen-rich stars. We notice additional period-luminosity sequence located between Wood's sequences C and C' and populated by SRVs.
Posted Content•
TL;DR: The OGLE-III catalog of variable stars as mentioned in this paper contains 23 R CrB (RCB) stars in the Large Magellanic Cloud (LMC). 17 of these objects have been spectroscopically confirmed by previous studies, while 6 stars are new candidates for RCB variables.
Abstract: The fifth part of the OGLE-III Catalog of Variable Stars presents 23 R CrB (RCB) stars in the Large Magellanic Cloud (LMC). 17 of these objects have been spectroscopically confirmed by previous studies, while 6 stars are new candidates for RCB variables. We publish the VI multi-epoch OGLE photometry for all objects.
We use the sample of carbon-rich long-period variables released in the previous part of this catalog to select objects with severe drops in luminosity, i.e. with the DY-Per-like light curves. DY Per stars are often related to R CrB variables. We detect at least 600 candidates for DY Per stars, mostly among dust enshrouded giants. We notice that our candidate DY Per stars form a continuity with other carbon-rich long-period variables, so it seems that DY Per stars do not constitute a separate group of variable stars.
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TL;DR: The third part of the OGLE-III catalog of variable stars comprises 24906 RR Lyr stars in the Large Magellanic Cloud (LMC). This sample consists of 17693 fundamental-mode (RRab), 4958 first-overtone (RRc), 986 double-mode(RRd) and 1269 suspected second-overlapping pulsators as discussed by the authors.
Abstract: The third part of the OGLE-III Catalog of Variable Stars comprises 24906 RR Lyr stars in the Large Magellanic Cloud (LMC). This sample consists of 17693 fundamental-mode (RRab), 4958 first-overtone (RRc), 986 double-mode (RRd) and 1269 suspected second-overtone (RRe) pulsators. 66 objects are foreground Galactic RR Lyr stars. The catalog data include basic photometric and astrometric properties of these RR Lyr stars, multi-epoch VI photometry and finding charts.
We detected one new RR Lyr star with additional eclipsing variations. The spatial distribution of RR Lyr stars in the LMC is distinctly non-spherical and it is elongated in the same direction as the LMC bar. The basic statistical features of RR Lyr stars in the LMC are provided. The apparent V-band magnitudes for RRab stars have the modal value at 19.36 mag, and for overtone RR Lyr stars it is about 19.32 mag. The mean periods for RRab, RRc and RRe stars are 0.576, 0.337 and 0.270 days, respectively.