153 research outputs found
Spitzer Parallax of OGLE-2018-BLG-0596: A Low-mass-ratio Planet around an M Dwarf
We report the discovery of a Spitzer microlensing planet OGLE-2018-BLG-0596Lb, with preferred planet-host mass ratio q ⌠2 x 10-4. The planetary signal, which is characterized by a short (âŒ1 day) bump on the rising side of the lensing light curve, was densely covered by ground-based surveys. We find that the signal can be explained by a bright source that fully envelops the planetary caustic, i.e., a Hollywood geometry. Combined with the source proper motion measured from Gaia, the Spitzer satellite parallax measurement makes it possible to precisely constrain the lens physical parameters. The preferred solution, in which the planet perturbs the minor image due to lensing by the host, yields a Uranus-mass planet with a mass of M p = 13.9 +1.6 M â orbiting a mid M-dwarf with a mass of M h = 0.23 +0.03 M o. There is also a second possible solution that is substantially disfavored but cannot be ruled out, for which the planet perturbs the major image. The latter solution yields M p = 1.2 +0.2 M â and M h = 0.15 +0.02 M o. By combining the microlensing and Gaia data together with a Galactic model, we find in either case that the lens lies on the near side of the Galactic bulge at a distance D L ⌠6 +1 kpc. Future adaptive optics observations may decisively resolve the major image/minor image degeneracy
Planet Sensitivity from Combined Ground- and Space-based Microlensing Observations
To move one step forward toward a Galactic distribution of planets, we
present the first planet sensitivity analysis for microlensing events with
simultaneous observations from space and the ground. We present this analysis
for two such events, OGLE-2014-BLG-0939 and OGLE-2014-BLG-0124, which both show
substantial planet sensitivity even though neither of them reached high
magnification. This suggests that an ensemble of low to moderate magnification
events can also yield significant planet sensitivity and therefore probability
to detect planets. The implications of our results to the ongoing and future
space-based microlensing experiments to measure the Galactic distribution of
planets are discussed.Comment: 10 pages, 5 figures, 1 table; ApJ in pres
OGLE-2005-BLG-153: Microlensing Discovery and Characterization of A Very Low Mass Binary
The mass function and statistics of binaries provide important diagnostics of
the star formation process. Despite this importance, the mass function at low
masses remains poorly known due to observational difficulties caused by the
faintness of the objects. Here we report the microlensing discovery and
characterization of a binary lens composed of very low-mass stars just above
the hydrogen-burning limit. From the combined measurements of the Einstein
radius and microlens parallax, we measure the masses of the binary components
of and . This discovery
demonstrates that microlensing will provide a method to measure the mass
function of all Galactic populations of very low mass binaries that is
independent of the biases caused by the luminosity of the population.Comment: 6 pages, 3 figures, 1 tabl
OGLE-2005-BLG-071Lb, the Most Massive M-Dwarf Planetary Companion?
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 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 D_l = 3.3 +/- 0.4 kpc, and thick-disk kinematics v_LSR ~
103 km/s. From the best-fit model, the planet has mass M_p = 3.8 +/- 0.4 M_Jup,
lies at a projected separation r_perp = 3.6 +/- 0.2 AU from its host and so has
an equilibrium temperature of T ~ 55 K, i.e., similar to Neptune. A degenerate
model less favored by \Delta\chi^2 = 2.1 (or 2.2, depending on the sign of the
impact parameter) gives similar planetary mass M_p = 3.4 +/- 0.4 M_Jup with a
smaller projected separation, r_\perp = 2.1 +/- 0.1 AU, 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.Comment: 51 pages, 12 figures, 3 tables, Published in Ap
Mass Production of 2021 KMTNet Microlensing Planets III: Analysis of Three Giant Planets
We present the analysis of three more planets from the KMTNet 2021
microlensing season. KMT-2021-BLG-0119Lb is a planet
orbiting an early M-dwarf or a K-dwarf, KMT-2021-BLG-0192Lb is a planet orbiting an M-dwarf, and KMT-2021-BLG-0192Lb is a planet orbiting a very--low-mass M dwarf or a brown dwarf.
These by-eye planet detections provide an important comparison sample to the
sample selected with the AnomalyFinder algorithm, and in particular,
KMT-2021-BLG-2294, is a case of a planet detected by-eye but not by-algorithm.
KMT-2021-BLG-2294Lb is part of a population of microlensing planets around
very-low-mass host stars that spans the full range of planet masses, in
contrast to the planet population at au, which shows a strong
preference for small planets.Comment: 17 pages, 12 figures, 7 tables. Accept for publication in The
Astronomical Journa
An analysis of binary microlensing event OGLE-2015-BLG-0060
We present the analysis of stellar binary microlensing event OGLE-2015-BLG-0060 based on observations obtained from 13 different telescopes. Intensive coverage of the anomalous parts of the light curve was achieved by automated follow-up observations from the robotic telescopes of the Las Cumbres Observatory. We show that, for the first time, all main features of an anomalous microlensing event are well covered by follow-up data, allowing us to estimate the physical parameters of the lens. The strong detection of second-order effects in the event light curve necessitates the inclusion of longer-baseline survey data in order to constrain the parallax vector. We find that the event was most likely caused by a stellar binary-lens with masses Mâ1=0.87±0.12Mâ and Mâ2=0.77±0.11Mââ . The distance to the lensing system is 6.41 ± 0.14 kpc and the projected separation between the two components is 13.85 ± 0.16 AU. Alternative interpretations are also considered
A New Type of Ambiguity in the Planet and Binary Interpretations of Central Perturbations of High-Magnification Gravitational Microlensing Events
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 basically 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 2 high-magnification events of OGLE-2011-BLG-0526 and
OGLE-2011-BLG-0950/MOA-2011-BLG-336. For OGLE-2011-BLG-0526, the
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 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 2 events observed during a single season suffer from such a degeneracy, it
is expected that central perturbations experiencing this type of degeneracy is
common.Comment: 8 pages, 8 figure
Observation of associated near-side and away-side long-range correlations in âsNN=5.02ââTeV proton-lead collisions with the ATLAS detector
Two-particle correlations in relative azimuthal angle (ÎÏ) and pseudorapidity (Îη) are measured in âsNN=5.02ââTeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1ââÎŒb-1 of data as a function of transverse momentum (pT) and the transverse energy (ÎŁETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Îη|<5) ânear-sideâ (ÎÏâŒ0) correlation that grows rapidly with increasing ÎŁETPb. A long-range âaway-sideâ (ÎÏâŒÏ) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ÎŁETPb, is found to match the near-side correlation in magnitude, shape (in Îη and ÎÏ) and ÎŁETPb dependence. The resultant ÎÏ correlation is approximately symmetric about Ï/2, and is consistent with a dominant cosâĄ2ÎÏ modulation for all ÎŁETPb ranges and particle pT
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