We present the analysis of MOA-2007-BLG-197Lb, the first brown dwarf companion to a Sun-like star detected through gravitational microlensing. The event was alerted and followed-up photometrically by ...a network of telescopes from the PLANET, MOA, and μFUN collaborations, and observed at high angular resolution using the NaCo instrument at the VLT. From the modelling of the microlensing light curve, we derived basic parameters such as, the binary lens separation in Einstein radius units (s ≃ 1.13), the mass ratio q = (4.732 ± 0.020) × 10-2 and the Einstein radius crossing time (tE ≃ 82 d). Because of this long time scale, we took annual parallax and orbital motion of the lens in the models into account, as well as finite source effects that were clearly detected during the source caustic exit. To recover the lens system’s physical parameters, we combined the resulting light curve best-fit parameters with (J,H,Ks) magnitudes obtained with VLT NaCo and calibrated using IRSF and 2MASS data. From this analysis, we derived a lens total mass of 0.86 ± 0.04 M⊙ and a lens distance of DL = 4.2 ± 0.3 kpc. We find that the companion of MOA-2007-BLG-197L is a brown dwarf of 41 ± 2 MJ observed at a projected separation of a⊥ = 4.3 ± 0.1 AU, and orbits a 0.82 ± 0.04 M⊙ G-K dwarf star. We then placed the companion of MOA-2007-BLG-197L in a mass-period diagram consisting of all brown dwarf companions detected so far through different techniques, including microlensing, transit, radial velocity, and direct imaging (most of these objects orbit solar-type stars). To study the statistical properties of this population, we performed a two-dimensional, non-parametric probability density distribution fit to the data, which draws a structured brown dwarf landscape. We confirm the existence of a region that is strongly depleted in objects at short periods and intermediate masses (P ≲ 30 d, M ~ 30−60 MJ), but also find an accumulation of objects around P ~ 500 d and M ~ 20 MJ, as well as another depletion region at long orbital periods (P ≳ 500 d) and high masses (M ≳ 50 MJ). While these data provide important clues on the different physical mechanisms of formation (or destruction) that shape the brown dwarf desert, more data are needed to establish their relative importance, in particular as a function of host star mass. Future microlensing surveys should soon provide more detections, in particular for red dwarf hosts, thus uniquely complementing the solar-type host sample.
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We analyze the planetary microlensing event MOA-2010-BLG-328. The best fit yields host and planetary masses of M sub(h) = 0.11 + or - 0.01 M sub(middot in circle) and M sub(p) = 9.2 + or - 2.2 M ...sub(+ in circle), corresponding to a very late M dwarf and sub-Neptune-mass planet, respectively. The system lies at D sub(L) = 0.81 + or - 0.10 kpc with projected separation r sub(bottom) = 0.92 + or - 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.
We report the discovery of a several-Jupiter mass planetary companion to the primary lens star in microlensing event OGLE-2005-BLG-071. Precise (<1%) photometry at the peak of the event yields an ...extremely high signal-to-noise ratio detection of a deviation from the light curve expected from an isolated lens. The planetary character of this deviation is easily and unambiguously discernible from the gross features of the light curve. Detailed modeling yields a tightly-constrained planet-star mass ratio of q=m_p/M=0.0071+/-0.0003. This is the second robust detection of a planet with microlensing, demonstrating that the technique itself is viable and that planets are not rare in the systems probed by microlensing, which typically lie several kpc toward the Galactic center.
We report on the evolution of the timing of 4U1630-47 during its 1998 outburst using data obtained with the Rossi X-ray Timing Explorer (RXTE). The count rate and position in hardness-intensity, ...color-color diagrams and simple spectral fits are used to track the concurrent spectral changes. The source showed seven distinct types of timing behavior, most of which show differences with the canonical black hole spectral/timing states. In marked contrast to previous outbursts, we find quasi-periodic oscillation (QPO) signals during nearly all stages of the outburst with frequencies between 0.06Hz and 14Hz and a remarkable variety of other characteristics. In particular we find large (up to 23% rms) amplitude QPO on the early rise. Later, slow 0.1Hz semi- regular short (~ 5 sec), 9 to 16% deep dips dominate the light curve. At this time there are two QPOs, one stable near 13.5Hz and the other whose frequency drops from 6--8Hz to ~4.5 Hz during the dips. BeppoSAX observations during the very late declining phase show 4U1630-47 in a low state.
Cyg X-3 is an unusual X-ray binary which shows remarkable correlative
behavior between the hard X-ray, soft X-ray, and the radio. We present an
analysis of these long term light curves in the context ...of spectral changes of
the system. This analysis will also incorporate a set of pointed RXTE
observations made during a period when Cyg X-3 made a transition from a
quiescent radio state to a flaring state (including a major flare) and then
returned to a quiescent radio state.
We present an analysis of the anomalous micro-lensing event,MOA-2010-BLG-073, announced by the Micro-lensing 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. We initially explored a number of purely micro-lensing models for the event but found a residual gradient in the data taken prior to and after the event. The Einstein crossing time of the event, tsubE = 44.3 + or - 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, DL = 2.8 + or - 0.4 kpc, and the masses of the lensing objects.
Pluto and its main satellite, Charon, occulted the same star on 2008 June 22. This event was observed from Australia and La Reunion Island, providing the east and north Charon Plutocentric offset in ...the sky plane (J2000): X= + 12,070.5 ? 4 km (+ 546.2 ? 0.2 mas), Y= + 4,576.3 ? 24 km (+ 207.1 ? 1.1 mas) at 19:20:33.82 UT on Earth, corresponding to JD 2454640.129964 at Pluto. This yields Charon's true longitude L= 153.483 ? 0071 in the satellite orbital plane (counted from the ascending node on J2000 mean equator) and orbital radius r= 19,564 ? 14 km at that time. We compare this position to that predicted by (1) the orbital solution of Tholen & Buie (the 'TB97' solution), (2) the PLU017 Charon ephemeris, and (3) the solution of Tholen et al. (the 'T08' solution). We conclude that (1) our result rules out solution TB97, (2) our position agrees with PLU017, with differences of Delta *DL= + 0.073 ? 0071 in longitude, and Delta *Dr= + 0.6 ? 14 km in radius, and (3) while the difference with the T08 ephemeris amounts to only Delta *DL= 0.033 ? 0071 in longitude, it exhibits a significant radial discrepancy of Delta *Dr= 61.3 ? 14 km. We discuss this difference in terms of a possible image scale relative error of 3.35 X 10--3in the 2002-2003 Hubble Space Telescope images upon which the T08 solution is mostly based. Rescaling the T08 Charon semi-major axis, a = 19, 570.45 km, to the TB97 value, a = 19636 km, all other orbital elements remaining the same ('T08/TB97' solution), we reconcile our position with the re-scaled solution by better than 12 km (or 0.55 mas) for Charon's position in its orbital plane, thus making T08/TB97 our preferred solution.
MOA-2010-BLG-523: “FAILED PLANET” = RS CVn STAR Gould, A; Yee, J C; Bond, I A ...
Astrophysical journal/The Astrophysical journal,
02/2013, Volume:
763, Issue:
2
Journal Article, Web Resource
Peer reviewed
Open access
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) ~ 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.
Cyg X-3 is an unusual X-ray binary which shows remarkable correlative behavior between the hard X-ray, soft X-ray, and the radio. We present an analysis of these long term light curves in the context ...of spectral changes of the system. This analysis will also incorporate a set of pointed RXTE observations made during a period when Cyg X-3 made a transition from a quiescent radio state to a flaring state (including a major flare) and then returned to a quiescent radio state.
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(middot in circle) and 0.39 M sub(middot in circle) for MOA-2011-BLG-090 and 0.57 M sub(middot in circle) and 0.17 M sub(middot in circle) 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.
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