The lowest mass ratio planetary microlens: OGLE 2016–BLG–1195Lb
Massey University1, Goddard Space Flight Center2, Osaka University3, University of Warsaw4, University of Auckland5, Istituto Nazionale di Fisica Nucleare6, University of Salerno7, Nagoya University8, University of Notre Dame9, College of Industrial Technology10, Victoria University of Wellington11, University of Canterbury12, Kyoto Sangyo University13, Ohio State University14, University of Warwick15
01 Aug 2017-Monthly Notices of the Royal Astronomical Society (Oxford University Press)-Vol. 469, Iss: 2, pp 2434-2440
TL;DR: In this paper, the authors reported the discovery of the lowest mass ratio exoplanet to be found by the microlensing method in the light curve of the event OGLE 2016 -BLG-1195.
Abstract: We report discovery of the lowest mass ratio exoplanet to be found by the microlensing method in the light curve of the event OGLE 2016 –BLG–1195. This planet revealed itself as a smalldeviation from a microlensing single lens profile from an examination of the survey data. Theduration of the planetary signal is ~ 2.5 h. The measured ratio of the planet mass to its hos tstar is q = 4.2 ± 0.7 x 10 -5(exp). We further estimate that the lens system is likely to comprise a cold ~3 Earth mass planet in an ~2 au wide orbit around a 0.2 Solar mass star at an overall distance of 7.1 kpc.
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TL;DR: In this paper, it was shown that Earth mass planets orbiting stars in the Galactic disk and bulge can be detected by monitoring microlensed stars in a Galactic bulge, and that the planetary signal remains detectable for planetary masses as small as an Earth mass when realistic source star sizes are included in the lightcurve calculation.
Abstract: We show that Earth mass planets orbiting stars in the Galactic disk and bulge can be detected by monitoring microlensed stars in the Galactic bulge. The star and its planet act as a binary lens which generates a lightcurve which can differ substantially from the lightcurve due only to the star itself. We show that the planetary signal remains detectable for planetary masses as small as an Earth mass when realistic source star sizes are included in the lightcurve calculation. These planets are detectable if they reside in the ``lensing zone" which is centered between 1 and 4 AU from the lensing star and spans about a factor of 2 in distance. If we require a minimum deviation of 4\% from the standard point-lens microlensing lightcurve, then we find that more than 2\% of all $\mearth$ planets and 10\% of all $10\mearth$ in the lensing zone can be detected. If a third of all lenses have no planets, a third have $1\mearth$ planets and the remaining third have $10\mearth$ planets then we estimate that an aggressive ground based microlensing planet search program could find one earth mass planet and half a dozen $10\mearth$ planets per year.
210 citations
TL;DR: The Wide Field InfraRed Survey Telescope (WFIRST) was chosen as the top-priority large space mission of the 2010 astronomy and astrophysics decadal survey in order to study dark energy via a wide field imaging survey, to study exoplanets via a microlensing survey, and to enable a guest observer program as mentioned in this paper.
Abstract: The Wide Field InfraRed Survey Telescope (WFIRST) is the next NASA astrophysics flagship mission, to follow the James Webb Space Telescope. The WFIRST mission was chosen as the top-priority large space mission of the 2010 astronomy and astrophysics decadal survey in order to achieve three primary goals: to study dark energy via a wide-field imaging survey, to study exoplanets via a microlensing survey, and to enable a guest observer program. Here we assess the ability of the several WFIRST designs to achieve the goal of the microlensing survey to discover a large sample of cold, low-mass exoplanets with semimajor axes beyond roughly one astronomical unit, which are largely impossible to detect with any other technique. We present the results of a suite of simulations that span the full range of the proposed WFIRST architectures, from the original design envisioned by the decadal survey, to the current design, which utilizes a 2.4 m telescope donated to NASA. By studying such a broad range of architectures, we are able to determine the impact of design trades on the expected yields of detected exoplanets. In estimating the yields we take particular care to ensure that our assumed Galactic model predicts microlensing event rates that match observations, consider the impact that inaccuracies in the Galactic model might have on the yields, and ensure that numerical errors in light-curve computations do not bias the yields for the smallest-mass exoplanets. For the nominal baseline WFIRST design and a fiducial planet mass function, we predict that a total of ∼1400 bound exoplanets with mass greater than ∼0.1 M ⊕ should be detected, including ∼200 with mass 3 M ⊕. WFIRST should have sensitivity to planets with mass down to ∼0.02 M ⊕ , or roughly the mass of Ganymede.
145 citations
Goddard Space Flight Center1, University of Maryland, College Park2, University of Tasmania3, Institut d'Astrophysique de Paris4, Space Telescope Science Institute5, University of Tokyo6, University of California, Berkeley7, Massey University8, NASA Exoplanet Science Institute9, Osaka University10, University of Warsaw11
TL;DR: In this article, an analysis of the simultaneous high-resolution images from the Hubble Space Telescope and Keck adaptive optics system of the planetary event OGLE-2012-BLG-0950 was presented.
Abstract: We present the analysis of the simultaneous high-resolution images from the Hubble Space Telescope and Keck adaptive optics system of the planetary event OGLE-2012-BLG-0950 that determine that the system consists of a 0.58 ± 0.04 M_⊕ host star orbited by a 39 ± 8 M_⊕ planet at a projected separation of 2.54 ± 0.23 au. The planetary system is located at a distance of 2.19 ± 0.23 kpc from Earth. This is the second microlens planet beyond the snow line with a mass measured to be in the mass range 20–80 M_⊕. The runaway gas accretion process of the core accretion model predicts fewer planets in this mass range. This is because giant planets are thought to be growing rapidly at these masses, and they rarely complete growth at this mass. So this result suggests that the core accretion theory may need revision. This analysis also demonstrates the techniques that will be used to measure the masses of planets and their host stars by the WFIRST exoplanet microlensing survey: one-dimensional microlensing parallax combined with the separation and brightness measurement of the unresolved source and host stars to yield multiple redundant constraints on the masses and distance of the planetary system.
74 citations
Cites methods from "The lowest mass ratio planetary mic..."
...Our re-analysis uses the same data set used by Koshimoto et al. (2017a) except that the MOA-II survey light curve data have been re-reduced using the procedure described in Bond et al. (2017)....
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TL;DR: In this paper, the authors present the analysis of the simultaneous high resolution images from the Hubble Space Telescope and Keck Adaptive Optics system of the planetary event OGLE-2012-BLG-0950 that determine that the system consists of a $058 \pm 004 \rm{M}_\odot$ host star orbited by a $39\pm 8 \rm {M}-_\oplus$ planet of at projected separation of $254 \pm 023\,$AU The planetary system is located at a distance of $
Abstract: We present the analysis of the simultaneous high resolution images from the {\it Hubble Space Telescope} and Keck Adaptive Optics system of the planetary event OGLE-2012-BLG-0950 that determine that the system consists of a $058 \pm 004 \rm{M}_\odot$ host star orbited by a $39\pm 8 \rm{M}_\oplus$ planet of at projected separation of $254 \pm 023\,$AU The planetary system is located at a distance of $219\pm 023$ kpc from Earth This is the second microlens planet beyond the snow line with a mass measured to be in the mass range $20$--$80 \rm{M}_\oplus$ The runaway gas accretion process of the core accretion model predicts few planets in this mass range, because giant planets are thought to be growing rapidly at these masses and they rarely complete growth at this mass So, this result suggests that the core accretion theory may need revision This analysis also demonstrates the techniques that will be used to measure the masses of planets and their host stars by the WFIRST exoplanet microlensing survey: one-dimensional microlensing parallax combined with the separation and brightness measurement of the unresolved source and host stars to yield multiple redundant constraints on the masses and distance of the planetary system
62 citations
TL;DR: The Wide Field InfraRed Survey Telescope (WFIRST) was chosen as the top-priority large space mission of the 2010 astronomy and astrophysics decadal survey in order to study dark energy via a wide field imaging survey, to study exoplanets via a microlensing survey, and to enable a guest observer program.
Abstract: The Wide Field InfraRed Survey Telescope (WFIRST) is the next NASA astrophysics flagship mission, to follow the James Webb Space Telescope (JWST). The WFIRST mission was chosen as the top-priority large space mission of the 2010 astronomy and astrophysics decadal survey in order to achieve three primary goals: to study dark energy via a wide-field imaging survey, to study exoplanets via a microlensing survey, and to enable a guest observer program. Here we assess the ability of the several WFIRST designs to achieve the goal of the microlensing survey to discover a large sample of cold, low-mass exoplanets with semimajor axes beyond roughly one AU, which are largely impossible to detect with any other technique. We present the results of a suite of simulations that span the full range of the proposed WFIRST architectures, from the original design envisioned by the decadal survey, to the current design, which utilizes a 2.4-m telescope donated to NASA. By studying such a broad range of architectures, we are able to determine the impact of design trades on the expected yields of detected exoplanets. In estimating the yields we take particular care to ensure that our assumed Galactic model predicts microlensing event rates that match observations, consider the impact that inaccuracies in the Galactic model might have on the yields, and ensure that numerical errors in lightcurve computations do not bias the yields for the smallest mass exoplanets. For the nominal baseline WFIRST design and a fiducial planet mass function, we predict that a total of ${\sim}1400$ bound exoplanets with mass greater than ${\sim}0.1~M_{\oplus}$ should be detected, including ${\sim}200$ with mass ${\lesssim}3~M_{\oplus}$. WFIRST should have sensitivity to planets with mass down to ${\sim}0.02~M_{\oplus}$, or roughly the mass of Ganymede.
55 citations
References
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TL;DR: In this article, the authors present a catalog of nearby exoplanets, which contains the 172 known low-mass companions with orbits established through radial velocity and transit measurements around stars within 200 pc, including five previously unpublished ex-oplanets orbiting the stars HD 11964, HD 66428, HD 99109, HD 107148 and HD 164922.
Abstract: We present a catalog of nearby exoplanets. It contains the 172 known low-mass companions with orbits established through radial velocity and transit measurements around stars within 200 pc. We include five previously unpublished exoplanets orbiting the stars HD 11964, HD 66428, HD 99109, HD 107148, and HD 164922. We update orbits for 83 additional exoplanets, including many whose orbits have not been revised since their announcement, and include radial velocity time series from the Lick, Keck, and Anglo-Australian Observatory planet searches. Both these new and previously published velocities are more precise here due to improvements in our data reduction pipeline, which we applied to archival spectra. We present a brief summary of the global properties of the known exoplanets, including their distributions of orbital semimajor axis, minimum mass, and orbital eccentricity.
968 citations
"The lowest mass ratio planetary mic..." refers background in this paper
...Of the approximately 3500 extrasolar planets so far discovered, most have been detected by the radial velocity technique (Butler et al. 2006) or transit technique (Mullally et al. 2015)....
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TL;DR: In this paper, the authors generalize the theory to the case of space-varying kernels and show that the CPU cost required for this new extension of the method is almost the same as for fitting a constant kernel solution.
Abstract: Image subtraction is a method by which one image is matched against another by using a convolution kernel, so that they can be differenced to detect and measure variable objects. It has been demonstrated that constant optimal-kernel solutions can be derived over small sub-areas of dense stellar fields. Here we generalize the theory to the case of space-varying kernels. In particular, it is shown that the CPU cost required for this new extension of the method is almost the same as for fitting a constant kernel solution. It is also shown that constant flux scaling between the images (constant kernel integral) can be imposed in a simple way. The method is demonstrated with a series of Monte-Carlo images. Differential PSF variations and differential rotation between the images are simulated. It is shown that the new method is able to achieve optimal results even in these difficult cases, thereby automatically correcting for these common instrumental problems. It is also demonstrated that the method does not suffer due to problems associated with under-sampling of the images. Finally, the method is applied to images taken by the OGLE II collaboration. It is proved that, in comparison to the constant-kernel method, much larger sub-areas of the images can be used for the fit, while still maintaining the same accuracy in the subtracted image. This result is especially important in case of variables located in low density fields, like the Huchra lens. Many other useful applications of the method are possible for major astrophysical problems; Supernova searches and Cepheids surveys in other galaxies, to mention but two. Many other applications will certainly show-up, since variability searches are a major issue in astronomy.
947 citations
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...For offline analysis, we use our own implementation that incorporates a numerical kernel as described by Bramich (2008) with our own modification to allow for a spatial variation of the kernel across the field of view in a similar manner to that given by Alard (2000)....
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TL;DR: In this article, a point-spread function (PSF) fitting photometry program, DOPHOT, is described and the quality of the resulting photometry is assessed via reductions of an 'artificial' globular cluster generated from a list of stars with known magnitudes and colors.
Abstract: The design considerations and operational features of DOPHOT, a point-spread function (PSF) fitting photometry program, are described. Some relevant details of the PSF fitting are discussed. The quality of the photometry returned by DOPHOT is assessed via reductions of an 'artificial' globular cluster generated from a list of stars with known magnitudes and colors. Results from comparative tests between DOPHOT and DAOPHOT using this synthetic cluster and real data are also described.
896 citations
"The lowest mass ratio planetary mic..." refers methods in this paper
...The DOPHOT photometry software (Schechter et al. 1993) was run on the difference imaging reference images for each of the RMOA and RMOA passbands....
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TL;DR: In this paper, it is estimated that about 10 percent of all lensing episodes of the Galactic bulge stars will strongly display the binary nature of the lens, even if the companion is a planet.
Abstract: Almost all stars are in binary systems. When the separation between the two components is comparable to the Einstein ring radius corresponding to the combined mass of the binary acting as a gravitational lens, then an extra pair of images can be created, and the light curve of a lensed source becomes complicated. It is estimated that about 10 percent of all lensing episodes of the Galactic bulge stars will strongly display the binary nature of the lens. The effect is strong even if the companion is a planet. A massive search for microlensing of the Galactic bulge stars may lead to a discovery of the first extrasolar planetary systems.
678 citations
"The lowest mass ratio planetary mic..." refers methods in this paper
...1 IN T RO D U C T I O N In the technique of gravitational microlensing, planetary systems are utilized as naturally occurring lenses of light from background source stars (Mao & Paczynski 1991; Gould & Loeb 1992; Bolatto & Falco 1994)....
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Institut d'Astrophysique de Paris1, University of Notre Dame2, Paul Sabatier University3, University of St Andrews4, Niels Bohr Institute5, European Southern Observatory6, University of Tasmania7, Australian National University8, University of Canterbury9, University of the Free State10, Lawrence Livermore National Laboratory11, University of Potsdam12, Vienna University of Technology13, University of Florida14, Space Telescope Science Institute15, Heidelberg University16, Liverpool John Moores University17, Queen's University Belfast18, University of Concepción19, University of Manchester20, Princeton University21, Nagoya University22, Massey University23, University of Auckland24, Victoria University of Wellington25
TL;DR: The detection of a cool, sub-Neptune-mass planets may be more common than gas giant planets, as predicted by the core accretion theory, and is suggested to name OGLE-2005-BLG-390Lb, indicating a planetary mass companion to the lens star of the microlensing event.
Abstract: Over 170 extrasolar planets have so far been discovered, with a wide range of masses and orbital periods, but until last July no planet of Neptune's mass or less had been detected any more than 0.15 astronomical units (AU) from a normal star. (That's close — Earth is one AU from the Sun). On 11 July 2005 the OGLE Early Warning System recorded a notable event: gravitational lensing of light from a distant object by a foreground star revealed a small planet of about 5.5 Earth masses, orbiting at about 2.6 AU from the foreground star. This is the lowest known mass for an extrasolar planet orbiting a main sequence star, and its detection suggests that cool, sub-Neptune mass planets are more common than gas giants, as predicted by the favoured core accretion theory of planet formation. In the favoured core-accretion model of formation of planetary systems, solid planetesimals accumulate to build up planetary cores, which then accrete nebular gas if they are sufficiently massive. Around M-dwarf stars (the most common stars in our Galaxy), this model favours the formation of Earth-mass (M⊕) to Neptune-mass planets with orbital radii of 1 to 10 astronomical units (au), which is consistent with the small number of gas giant planets known to orbit M-dwarf host stars1,2,3,4. More than 170 extrasolar planets have been discovered with a wide range of masses and orbital periods, but planets of Neptune's mass or less have not hitherto been detected at separations of more than 0.15 au from normal stars. Here we report the discovery of a M⊕ planetary companion at a separation of au from a M⊙ M-dwarf star, where M⊙ refers to a solar mass. (We propose to name it OGLE-2005-BLG-390Lb, indicating a planetary mass companion to the lens star of the microlensing event.) The mass is lower than that of GJ876d (ref. 5), although the error bars overlap. Our detection suggests that such cool, sub-Neptune-mass planets may be more common than gas giant planets, as predicted by the core accretion theory.
636 citations
"The lowest mass ratio planetary mic..." refers background or result in this paper
...We can compare this to the similar case of OGLE 2005–BLG–390 where a binary source model was excluded in favour of a planetary model at χ2 ≈ 46 (Beaulieu et al. 2006)....
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...This planet is the sixth microlens planet with a sub-10−4 mass ratio – the others being OGLE-2013BLG-0341LBb, OGLE 2005–BLG–390Lb (Beaulieu et al. 2006), OGLE 2005–BLG–169Lb (Gould et al. 2006; Bennett et al. 2015; Batista et al. 2015), OGLE-2007-BLG-368Lb (Sumi et al. 2010) and MOA 2009–BLG-266Lb…...
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