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See detailMOA-2010-BLG-311: A planetary candidate below the threshold of reliable detection
Yee, J. C.; Hung, L.-W.; Bond, I. A. et al

in Astrophysical Journal (2013), 769(1), 77

We analyze MOA-2010-BLG-311, a high magnification (A_max>600) microlensing event with complete data coverage over the peak, making it very sensitive to planetary signals. We fit this event with both a ... [more ▼]

We analyze MOA-2010-BLG-311, a high magnification (A_max>600) microlensing event with complete data coverage over the peak, making it very sensitive to planetary signals. We fit this event with both a point lens and a 2-body lens model and find that the 2-body lens model is a better fit but with only Delta chi^2~140. The preferred mass ratio between the lens star and its companion is $q=10^(-3.7+/-0.1), placing the candidate companion in the planetary regime. Despite the formal significance of the planet, we show that because of systematics in the data the evidence for a planetary companion to the lens is too tenuous to claim a secure detection. When combined with analyses of other high-magnification events, this event helps empirically define the threshold for reliable planet detection in high-magnification events, which remains an open question. [less ▲]

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See detailMicrolensing Discovery of a Population of Very Tight, Very Low Mass Binary Brown Dwarfs
Choi, J.-Y.; Han, C.; Udalski, A. et al

in Astrophysical Journal (2013), 768

Although many models have been proposed, the physical mechanisms responsible for the formation of low-mass brown dwarfs (BDs) are poorly understood. The multiplicity properties and minimum mass of the BD ... [more ▼]

Although many models have been proposed, the physical mechanisms responsible for the formation of low-mass brown dwarfs (BDs) are poorly understood. The multiplicity properties and minimum mass of the BD mass function provide critical empirical diagnostics of these mechanisms. We present the discovery via gravitational microlensing of two very low mass, very tight binary systems. These binaries have directly and precisely measured total system masses of 0.025 M [SUB]⊙[/SUB] and 0.034 M [SUB]⊙[/SUB], and projected separations of 0.31 AU and 0.19 AU, making them the lowest-mass and tightest field BD binaries known. The discovery of a population of such binaries indicates that BD binaries can robustly form at least down to masses of ~0.02 M [SUB]⊙[/SUB]. Future microlensing surveys will measure a mass-selected sample of BD binary systems, which can then be directly compared to similar samples of stellar binaries. [less ▲]

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See detailA giant planet beyond the snow line in microlensing event OGLE-2011-BLG-0251
Kains, N.; Street, R. A.; Choi, J.-Y. et al

in Astronomy and Astrophysics (2013), 552

<BR /> Aims: We present the analysis of the gravitational microlensing event OGLE-2011-BLG-0251. This anomalous event was observed by several survey and follow-up collaborations conducting microlensing ... [more ▼]

<BR /> Aims: We present the analysis of the gravitational microlensing event OGLE-2011-BLG-0251. This anomalous event was observed by several survey and follow-up collaborations conducting microlensing observations towards the Galactic bulge. <BR /> Methods: Based on detailed modelling of the observed light curve, we find that the lens is composed of two masses with a mass ratio q = 1.9 × 10[SUP]-3[/SUP]. Thanks to our detection of higher-order effects on the light curve due to the Earth's orbital motion and the finite size of source, we are able to measure the mass and distance to the lens unambiguously. <BR /> Results: We find that the lens is made up of a planet of mass 0.53 ± 0.21 M[SUB]J[/SUB] orbiting an M dwarf host star with a mass of 0.26 ± 0.11 M[SUB]⊙[/SUB]. The planetary system is located at a distance of 2.57 ± 0.61 kpc towards the Galactic centre. The projected separation of the planet from its host star is d = 1.408 ± 0.019, in units of the Einstein radius, which corresponds to 2.72 ± 0.75 AU in physical units. We also identified a competitive model with similar planet and host star masses, but with a smaller orbital radius of 1.50 ± 0.50 AU. The planet is therefore located beyond the snow line of its host star, which we estimate to be around ~1-1.5 AU. [less ▲]

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See detailFlux and color variations of the doubly imaged quasar UM673
Ricci, Davide ULg; Elyiv, Andrii ULg; Finet, François ULg et al

in Astronomy and Astrophysics (2013), 551

With the aim of characterizing the flux and color variations of the multiple components of the gravitationally lensed quasar UM673 as a function of time, we have performed multi-epoch and multi-band ... [more ▼]

With the aim of characterizing the flux and color variations of the multiple components of the gravitationally lensed quasar UM673 as a function of time, we have performed multi-epoch and multi-band photometric observations with the Danish 1.54m telescope at the La Silla Observatory. The observations were carried out in the VRi spectral bands during four seasons (2008--2011). We reduced the data using the PSF (Point Spread Function) photometric technique as well as aperture photometry. Our results show for the brightest lensed component some significant decrease in flux between the first two seasons (+0.09/+0.11/+0.05 mag) and a subsequent increase during the following ones (-0.11/-0.11/-0.10 mag) in the V/R/i spectral bands, respectively. Comparing our results with previous studies, we find smaller color variations between these seasons as compared with previous ones. We also separate the contribution of the lensing galaxy from that of the fainter and close lensed component. [less ▲]

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See detailMOA-2010-BLG-523: "Failed Planet" = RS CVn Star
Gould, A.; Yee, J. C.; Bond, I. A. et al

in Astrophysical Journal (2013), 763

The Galactic bulge source MOA-2010-BLG-523S exhibited short-term deviations from a standard microlensing light curve near the peak of an A [SUB]max[/SUB] ~ 265 high-magnification microlensing event. The ... [more ▼]

The Galactic bulge source MOA-2010-BLG-523S exhibited short-term deviations from a standard microlensing light curve near the peak of an A [SUB]max[/SUB] ~ 265 high-magnification microlensing event. The deviations originally seemed consistent with expectations for a planetary companion to the principal lens. We combine long-term photometric monitoring with a previously published high-resolution spectrum taken near peak to demonstrate that this is an RS CVn variable, so that planetary microlensing is not required to explain the light-curve deviations. This is the first spectroscopically confirmed RS CVn star discovered in the Galactic bulge. Based on observations made with the European Southern Observatory telescopes, Program ID 85.B-0399(I). [less ▲]

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See detailMOA-2010-BLG-073L: An M-dwarf with a Substellar Companion at the Planet/Brown Dwarf Boundary
Street, R. A.; Choi, J.-Y.; Tsapras, Y. et al

in Astrophysical Journal (2013), 763

We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073, announced by the Microlensing Observations in Astrophysics survey on 2010 March 18. This event was remarkable because the ... [more ▼]

We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073, announced by the Microlensing Observations in Astrophysics survey on 2010 March 18. This event was remarkable because the source was previously known to be photometrically variable. Analyzing the pre-event source light curve, we demonstrate that it is an irregular variable over timescales >200 days. Its dereddened color, (V - I)[SUB] S, 0[/SUB], is 1.221 ± 0.051 mag, and from our lens model we derive a source radius of 14.7 ± 1.3 R [SUB]&sun;[/SUB], suggesting that it is a red giant star. We initially explored a number of purely microlensing models for the event but found a residual gradient in the data taken prior to and after the event. This is likely to be due to the variability of the source rather than part of the lensing event, so we incorporated a slope parameter in our model in order to derive the true parameters of the lensing system. We find that the lensing system has a mass ratio of q = 0.0654 ± 0.0006. The Einstein crossing time of the event, t [SUB]E[/SUB] = 44.3 ± 0.1 days, was sufficiently long that the light curve exhibited parallax effects. In addition, the source trajectory relative to the large caustic structure allowed the orbital motion of the lens system to be detected. Combining the parallax with the Einstein radius, we were able to derive the distance to the lens, D[SUB]L[/SUB] = 2.8 ± 0.4 kpc, and the masses of the lensing objects. The primary of the lens is an M-dwarf with M [SUB] L, 1[/SUB] = 0.16 ± 0.03 M [SUB]&sun;[/SUB], while the companion has M [SUB] L, 2[/SUB] = 11.0 ± 2.0 M [SUB]J[/SUB], putting it in the boundary zone between planets and brown dwarfs. [less ▲]

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See detailMOA-2010-BLG-328Lb: a sub-Neptune orbiting very late M dwarf ?
Furusawa, K.; Udalski, A.; Sumi, T. et al

in Astrophysical Journal (2013), 91

We analyze the planetary microlensing event MOA-2010-BLG-328. The best fit yields host and planetary masses of Mh = 0.11+/-0.01 M_{sun} and Mp = 9.2+/-2.2M_Earth, corresponding to a very late M dwarf and ... [more ▼]

We analyze the planetary microlensing event MOA-2010-BLG-328. The best fit yields host and planetary masses of Mh = 0.11+/-0.01 M_{sun} and Mp = 9.2+/-2.2M_Earth, corresponding to a very late M dwarf and sub-Neptune-mass planet, respectively. The system lies at DL = 0.81 +/- 0.10 kpc with projected separation r = 0.92 +/- 0.16 AU. Because of the host's a-priori-unlikely close distance, as well as the unusual nature of the system, we consider the possibility that the microlens parallax signal, which determines the host mass and distance, is actually due to xallarap (source orbital motion) that is being misinterpreted as parallax. We show a result that favors the parallax solution, even given its close host distance. We show that future high-resolution astrometric measurements could decisively resolve the remaining ambiguity of these solutions. [less ▲]

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See detailMicrolensing Binaries with Candidate Brown Dwarf Companions
Shin, I.-G.; Han, C.; Gould, A. et al

in Astrophysical Journal (2012), 760

Brown dwarfs are important objects because they may provide a missing link between stars and planets, two populations that have dramatically different formation histories. In this paper, we present the ... [more ▼]

Brown dwarfs are important objects because they may provide a missing link between stars and planets, two populations that have dramatically different formation histories. In this paper, we present the candidate binaries with brown dwarf companions that are found by analyzing binary microlensing events discovered during the 2004-2011 observation seasons. Based on the low mass ratio criterion of q < 0.2, we found seven candidate events: OGLE-2004-BLG-035, OGLE-2004-BLG-039, OGLE-2007-BLG-006, OGLE-2007-BLG-399/MOA-2007-BLG-334, MOA-2011-BLG-104/OGLE-2011-BLG-0172, MOA-2011-BLG-149, and MOA-201-BLG-278/OGLE-2011-BLG-012N. Among them, we are able to confirm that the companions of the lenses of MOA-2011-BLG-104/OGLE-2011-BLG-0172 and MOA-2011-BLG-149 are brown dwarfs by determining the mass of the lens based on the simultaneous measurement of the Einstein radius and the lens parallax. The measured masses of the brown dwarf companions are 0.02 ± 0.01 M [SUB]&sun;[/SUB] and 0.019 ± 0.002 M [SUB]&sun;[/SUB] for MOA-2011-BLG-104/OGLE-2011-BLG-0172 and MOA-2011-BLG-149, respectively, and both companions are orbiting low-mass M dwarf host stars. More microlensing brown dwarfs are expected to be detected as the number of lensing events with well-covered light curves increases with new-generation searches. [less ▲]

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See detailA New Type of Ambiguity in the Planet and Binary Interpretations of Central Perturbations of High-magnification Gravitational Microlensing Events
Choi, J.-Y.; Shin, I.-G.; Han, C. et al

in Astrophysical Journal (2012), 756

High-magnification microlensing events provide an important channel to detect planets. Perturbations near the peak of a high-magnification event can be produced either by a planet or a binary companion ... [more ▼]

High-magnification microlensing events provide an important channel to detect planets. Perturbations near the peak of a high-magnification event can be produced either by a planet or a binary companion. It is known that central perturbations induced by both types of companions can be generally distinguished due to the essentially different magnification pattern around caustics. In this paper, we present a case of central perturbations for which it is difficult to distinguish the planetary and binary interpretations. The peak of a lensing light curve affected by this perturbation appears to be blunt and flat. For a planetary case, this perturbation occurs when the source trajectory passes the negative perturbation region behind the back end of an arrowhead-shaped central caustic. For a binary case, a similar perturbation occurs for a source trajectory passing through the negative perturbation region between two cusps of an astroid-shaped caustic. We demonstrate the degeneracy for two high-magnification events of OGLE-2011-BLG-0526 and OGLE-2011-BLG-0950/MOA-2011-BLG-336. For OGLE-2011-BLG-0526, the χ[SUP]2[/SUP] difference between the planetary and binary model is ~3, implying that the degeneracy is very severe. For OGLE-2011-BLG-0950/MOA-2011-BLG-336, the stellar binary model is formally excluded with Δχ[SUP]2[/SUP] ~ 105 and the planetary model is preferred. However, it is difficult to claim a planet discovery because systematic residuals of data from the planetary model are larger than the difference between the planetary and binary models. Considering that two events observed during a single season suffer from such a degeneracy, it is expected that central perturbations experiencing this type of degeneracy is common. [less ▲]

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See detailOGLE-2008-BLG-510: first automated real-time detection of a weak microlensing anomaly - brown dwarf or stellar binary?
Bozza, V.; Dominik, M.; Rattenbury, N. J. et al

in Monthly Notices of the Royal Astronomical Society (2012), 424

The microlensing event OGLE-2008-BLG-510 is characterized by an evident asymmetric shape of the peak, promptly detected by the Automated Robotic Terrestrial Exoplanet Microlensing Search (ARTEMiS) system ... [more ▼]

The microlensing event OGLE-2008-BLG-510 is characterized by an evident asymmetric shape of the peak, promptly detected by the Automated Robotic Terrestrial Exoplanet Microlensing Search (ARTEMiS) system in real time. The skewness of the light curve appears to be compatible both with binary-lens and binary-source models, including the possibility that the lens system consists of an M dwarf orbited by a brown dwarf. The detection of this microlensing anomaly and our analysis demonstrate that: (1) automated real-time detection of weak microlensing anomalies with immediate feedback is feasible, efficient and sensitive, (2) rather common weak features intrinsically come with ambiguities that are not easily resolved from photometric light curves, (3) a modelling approach that finds all features of parameter space rather than just the 'favourite model' is required and (4) the data quality is most crucial, where systematics can be confused with real features, in particular small higher order effects such as orbital motion signatures. It moreover becomes apparent that events with weak signatures are a silver mine for statistical studies, although not easy to exploit. Clues about the apparent paucity of both brown-dwarf companions and binary-source microlensing events might hide here. Based in part on data collected by MiNDSTEp with the Danish 1.54m telescope at the ESO La Silla Observatory. [less ▲]

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See detailCharacterizing Low-mass Binaries from Observation of Long-timescale Caustic-crossing Gravitational Microlensing Events
Shin, I.-G.; Han, C.; Choi, J.-Y. et al

in Astrophysical Journal (2012), 755

Despite the astrophysical importance of binary star systems, detections are limited to those located in small ranges of separations, distances, and masses and thus it is necessary to use a variety of ... [more ▼]

Despite the astrophysical importance of binary star systems, detections are limited to those located in small ranges of separations, distances, and masses and thus it is necessary to use a variety of observational techniques for a complete view of stellar multiplicity across a broad range of physical parameters. In this paper, we report the detections and measurements of two binaries discovered from observations of microlensing events MOA-2011-BLG-090 and OGLE-2011-BLG-0417. Determinations of the binary masses are possible by simultaneously measuring the Einstein radius and the lens parallax. The measured masses of the binary components are 0.43 M [SUB]&sun;[/SUB] and 0.39 M [SUB]&sun;[/SUB] for MOA-2011-BLG-090 and 0.57 M [SUB]&sun;[/SUB] and 0.17 M [SUB]&sun;[/SUB] for OGLE-2011-BLG-0417 and thus both lens components of MOA-2011-BLG-090 and one component of OGLE-2011-BLG-0417 are M dwarfs, demonstrating the usefulness of microlensing in detecting binaries composed of low-mass components. From modeling of the light curves considering full Keplerian motion of the lens, we also measure the orbital parameters of the binaries. The blended light of OGLE-2011-BLG-0417 comes very likely from the lens itself, making it possible to check the microlensing orbital solution by follow-up radial-velocity observation. For both events, the caustic-crossing parts of the light curves, which are critical for determining the physical lens parameters, were resolved by high-cadence survey observations and thus it is expected that the number of microlensing binaries with measured physical parameters will increase in the future. [less ▲]

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See detailMOA 2010-BLG-477Lb: Constraining the Mass of a Microlensing Planet from Microlensing Parallax, Orbital Motion, and Detection of Blended Light
Bachelet, E.; Shin, I.-G.; Han, C. et al

in Astrophysical Journal (2012), 754

Microlensing detections of cool planets are important for the construction of an unbiased sample to estimate the frequency of planets beyond the snow line, which is where giant planets are thought to form ... [more ▼]

Microlensing detections of cool planets are important for the construction of an unbiased sample to estimate the frequency of planets beyond the snow line, which is where giant planets are thought to form according to the core accretion theory of planet formation. In this paper, we report the discovery of a giant planet detected from the analysis of the light curve of a high-magnification microlensing event MOA 2010-BLG-477. The measured planet-star mass ratio is q = (2.181 ± 0.004) × 10[SUP]-3[/SUP] and the projected separation is s = 1.1228 ± 0.0006 in units of the Einstein radius. The angular Einstein radius is unusually large θ[SUB]E[/SUB] = 1.38 ± 0.11 mas. Combining this measurement with constraints on the "microlens parallax" and the lens flux, we can only limit the host mass to the range 0.13 < M/M [SUB]&sun;[/SUB] < 1.0. In this particular case, the strong degeneracy between microlensing parallax and planet orbital motion prevents us from measuring more accurate host and planet masses. However, we find that adding Bayesian priors from two effects (Galactic model and Keplerian orbit) each independently favors the upper end of this mass range, yielding star and planet masses of M [SUB]*[/SUB] = 0.67[SUP]+0.33[/SUP] [SUB]- 0.13[/SUB] M [SUB]&sun;[/SUB] and m[SUB]p[/SUB] = 1.5[SUP]+0.8[/SUP] [SUB]- 0.3[/SUB] M [SUB]JUP[/SUB] at a distance of D = 2.3 ± 0.6 kpc, and with a semi-major axis of a = 2[SUP]+3[/SUP] [SUB]- 1[/SUB] AU. Finally, we show that the lens mass can be determined from future high-resolution near-IR adaptive optics observations independently from two effects, photometric and astrometric. [less ▲]

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See detailCharacterizing Lenses and Lensed Stars of High-magnification Single-lens Gravitational Microlensing Events with Lenses Passing over Source Stars
Choi, J.-Y.; Shin, I.-G.; Park, S.-Y. et al

in Astrophysical Journal (2012), 751

We present the analysis of the light curves of nine high-magnification single-lens gravitational microlensing events with lenses passing over source stars, including OGLE-2004-BLG-254, MOA-2007-BLG-176 ... [more ▼]

We present the analysis of the light curves of nine high-magnification single-lens gravitational microlensing events with lenses passing over source stars, including OGLE-2004-BLG-254, MOA-2007-BLG-176, MOA-2007-BLG-233/OGLE-2007-BLG-302, MOA-2009-BLG-174, MOA-2010-BLG-436, MOA-2011-BLG-093, MOA-2011-BLG-274, OGLE-2011-BLG-0990/MOA-2011-BLG-300, and OGLE-2011-BLG-1101/MOA-2011-BLG-325. For all of the events, we measure the linear limb-darkening coefficients of the surface brightness profile of source stars by measuring the deviation of the light curves near the peak affected by the finite-source effect. For seven events, we measure the Einstein radii and the lens-source relative proper motions. Among them, five events are found to have Einstein radii of less than 0.2 mas, making the lenses very low mass star or brown dwarf candidates. For MOA-2011-BLG-274, especially, the small Einstein radius of θ[SUB]E[/SUB] ~ 0.08 mas combined with the short timescale of t [SUB]E[/SUB] ~ 2.7 days suggests the possibility that the lens is a free-floating planet. For MOA-2009-BLG-174, we measure the lens parallax and thus uniquely determine the physical parameters of the lens. We also find that the measured lens mass of ~0.84 M [SUB]&sun;[/SUB] is consistent with that of a star blended with the source, suggesting that the blend is likely to be the lens. Although we did not find planetary signals for any of the events, we provide exclusion diagrams showing the confidence levels excluding the existence of a planet as a function of the separation and mass ratio. [less ▲]

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See detailMicrolensing Binaries Discovered through High-magnification Channel
Shin, I.-G.; Choi, J.-Y.; Park, S.-Y. et al

in Astrophysical Journal (2012), 746

Microlensing can provide a useful tool to probe binary distributions down to low-mass limits of binary companions. In this paper, we analyze the light curves of eight binary-lensing events detected ... [more ▼]

Microlensing can provide a useful tool to probe binary distributions down to low-mass limits of binary companions. In this paper, we analyze the light curves of eight binary-lensing events detected through the channel of high-magnification events during the seasons from 2007 to 2010. The perturbations, which are confined near the peak of the light curves, can be easily distinguished from the central perturbations caused by planets. However, the degeneracy between close and wide binary solutions cannot be resolved with a 3σ confidence level for three events, implying that the degeneracy would be an important obstacle in studying binary distributions. The dependence of the degeneracy on the lensing parameters is consistent with a theoretical prediction that the degeneracy becomes severe as the binary separation and the mass ratio deviate from the values of resonant caustics. The measured mass ratio of the event OGLE-2008-BLG-510/MOA-2008-BLG-369 is q ~ 0.1, making the companion of the lens a strong brown dwarf candidate. [less ▲]

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See detailA brown dwarf orbiting an M-dwarf: MOA 2009-BLG-411L
Bachelet, E.; Fouqué, P.; Han, C. et al

in Astronomy and Astrophysics (2012), 547

Context. Caustic crossing is the clearest signature of binary lenses in microlensing. In the present context, this signature is diluted by the large source star but a detailed analysis has allowed the ... [more ▼]

Context. Caustic crossing is the clearest signature of binary lenses in microlensing. In the present context, this signature is diluted by the large source star but a detailed analysis has allowed the companion signal to be extracted. <BR /> Aims: MOA 2009-BLG-411 was detected on August 5, 2009 by the MOA-Collaboration. Alerted as a high-magnification event, it was sensitive to planets. Suspected anomalies in the light curve were not confirmed by a real-time model, but further analysis revealed small deviations from a single lens extended source fit. <BR /> Methods: Thanks to observations by all the collaborations, this event was well monitored. We first decided to characterize the source star properties by using a more refined method than the classical one: we measure the interstellar absorption along the line of sight in five different passbands (VIJHK). Secondly, we model the lightcurve by using the standard technique: make (s,q,α) grids to look for local minima and refine the results by using a downhill method (Markov chain Monte Carlo). Finally, we use a Galactic model to estimate the physical properties of the lens components. <BR /> Results: We find that the source star is a giant G star with radius 9 R[SUB]&sun;[/SUB]. The grid search gives two local minima, which correspond to the theoretical degeneracy s ≡ s[SUP]-1[/SUP]. We find that the lens is composed of a brown dwarf secondary of mass M[SUB]S[/SUB] = 0.05 M[SUB]&sun;[/SUB] orbiting a primary M-star of mass M[SUB]P[/SUB] = 0.18 M[SUB]&sun;[/SUB]. We also reveal a new mass-ratio degeneracy for the central caustics of close binaries. <BR /> Conclusions: As far as we are aware, this is the first detection using the microlensing technique of a binary system in our Galaxy composed of an M-star and a brown dwarf. Appendix is available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detailDiscovery and Mass Measurements of a Cold, 10 Earth Mass Planet and Its Host Star
Muraki, Y.; Han, C.; Bennett, D. P. et al

in Astrophysical Journal (2011), 741

We present the discovery and mass measurement of the cold, low-mass planet MOA-2009-BLG-266Lb, performed with the gravitational microlensing method. This planet has a mass of m[SUB]p[/SUB] = 10.4 ± 1.7 M ... [more ▼]

We present the discovery and mass measurement of the cold, low-mass planet MOA-2009-BLG-266Lb, performed with the gravitational microlensing method. This planet has a mass of m[SUB]p[/SUB] = 10.4 ± 1.7 M[SUB]⊕[/SUB] and orbits a star of mass M [SUB]sstarf[/SUB] = 0.56 ± 0.09 M[SUB]sun[/SUB] at a semimajor axis of a = 3.2{+1.9\atop -0.5} AU and an orbital period of P = 7.6{+7.7\atop -1.5} yrs. The planet and host star mass measurements are enabled by the measurement of the microlensing parallax effect, which is seen primarily in the light curve distortion due to the orbital motion of the Earth. But the analysis also demonstrates the capability to measure the microlensing parallax with the Deep Impact (or EPOXI) spacecraft in a heliocentric orbit. The planet mass and orbital distance are similar to predictions for the critical core mass needed to accrete a substantial gaseous envelope, and thus may indicate that this planet is a "failed" gas giant. This and future microlensing detections will test planet formation theory predictions regarding the prevalence and masses of such planets. [less ▲]

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See detailMOA-2009-BLG-387Lb: a massive planet orbiting an M dwarf
Batista, V.; Gould, A.; Dieters, S. et al

in Astronomy and Astrophysics (2011), 529

<BR /> Aims: We report the discovery of a planet with a high planet-to-star mass ratio in the microlensing event MOA-2009-BLG-387, which exhibited pronounced deviations over a 12-day interval, one of the ... [more ▼]

<BR /> Aims: We report the discovery of a planet with a high planet-to-star mass ratio in the microlensing event MOA-2009-BLG-387, which exhibited pronounced deviations over a 12-day interval, one of the longest for any planetary event. The host is an M dwarf, with a mass in the range 0.07 M[SUB]&sun;[/SUB] < M[SUB]host[/SUB] < 0.49 M[SUB]&sun;[/SUB] at 90% confidence. The planet-star mass ratio q = 0.0132 ± 0.003 has been measured extremely well, so at the best-estimated host mass, the planet mass is m[SUB]p[/SUB] = 2.6 Jupiter masses for the median host mass, M = 0.19 M[SUB]&sun;[/SUB]. <BR /> Methods: The host mass is determined from two "higher order" microlensing parameters. One of these, the angular Einstein radius θ[SUB]E[/SUB] = 0.31 ± 0.03 mas has been accurately measured, but the other (the microlens parallax π[SUB]E[/SUB], which is due to the Earth's orbital motion) is highly degenerate with the orbital motion of the planet. We statistically resolve the degeneracy between Earth and planet orbital effects by imposing priors from a Galactic model that specifies the positions and velocities of lenses and sources and a Kepler model of orbits. <BR /> Results: The 90% confidence intervals for the distance, semi-major axis, and period of the planet are 3.5 kpc < D[SUB]L[/SUB] < 7.9 kpc, 1.1 AU < a < 2.7 AU, and 3.8 yr < P < 7.6 yr, respectively. Photometric data is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/529/A102">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/529/A102</A> [less ▲]

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See detailFlux and color variations of the quadruply imaged quasar HE 0435--1223
Ricci, Davide ULg; Poels, Joël ULg; Elyiv, Andrii ULg et al

in Astronomy and Astrophysics (2011), 528

We present VRi photometric observations of the quadruply imaged quasar HE 0435-1223, carried out with the Danish 1.54m telescope at the La Silla Observatory. Our aim was to monitor and study the ... [more ▼]

We present VRi photometric observations of the quadruply imaged quasar HE 0435-1223, carried out with the Danish 1.54m telescope at the La Silla Observatory. Our aim was to monitor and study the magnitudes and colors of each lensed component as a function of time. methods: We monitored the object during two seasons (2008 and 2009) in the VRi spectral bands, and reduced the data with two independent techniques: difference imaging and PSF (Point Spread Function) fitting.results: Between these two seasons, our results show an evident decrease in flux by ~0.2-0.4 magnitudes of the four lensed components in the three filters. We also found a significant increase (~0.05-0.015) in their V-R and R-i color indices. conclusions: These flux and color variations are very likely caused by intrinsic variations of the quasar between the observed epochs. Microlensing effects probably also affect the brightest "A" lensed component. [less ▲]

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See detailHE 0435-1223 lensed QSO VRi light curves (Ricci+, 2011)
Ricci, Davide ULg; Poels, Joël ULg; Elyiv, Andrii ULg et al

Textual, factual or bibliographical database (2011)

We present VRi photometric observations of the quadruply imaged quasar HE0435-1223, carried out with the Danish 1.54m telescope at the La Silla Observatory. Our aim was to monitor and study the magnitudes ... [more ▼]

We present VRi photometric observations of the quadruply imaged quasar HE0435-1223, carried out with the Danish 1.54m telescope at the La Silla Observatory. Our aim was to monitor and study the magnitudes and colors of each lensed component as a function of time. [less ▲]

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See detailFrequency of Solar-like Systems and of Ice and Gas Giants Beyond the Snow Line from High-magnification Microlensing Events in 2005-2008
Gould, A.; Dong, Subo; Gaudi, B. S. et al

in Astrophysical Journal (2010), 720

We present the first measurement of the planet frequency beyond the "snow line," for the planet-to-star mass-ratio interval –4.5 < log q < –2, corresponding to the range of ice giants to gas giants. We ... [more ▼]

We present the first measurement of the planet frequency beyond the "snow line," for the planet-to-star mass-ratio interval –4.5 < log q < –2, corresponding to the range of ice giants to gas giants. We find \endgraf\vbox{\begin{center}$\displaystyle{d^2 N{_{\rm pl}}\over d\log q\, d\log s} = (0.36\pm 0.15)\;{\rm dex}^{-2}$\end{center}}\noindentat the mean mass ratio q = 5 × 10 –4 with no discernible deviation from a flat (Öpik's law) distribution in log-projected separation s. The determination is based on a sample of six planets detected from intensive follow-up observations of high-magnification ( A>200) microlensing events during 2005-2008. The sampled host stars have a typical mass M host ~ 0.5 M sun [less ▲]

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