5 research outputs found
Characterizing Low-Mass Binaries From Observation of Long Time-scale Caustic-crossing Gravitational Microlensing Events
Despite 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 2
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 and 0.39
for MOA-2011-BLG-090 and 0.57 and 0.17 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.Comment: 8 pages, 5 figures, 4 table
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
CHARACTERIZING LOW-MASS BINARIES FROM OBSERVATION OF LONG-TIMESCALE CAUSTIC-CROSSING GRAVITATIONAL MICROLENSING EVENTS
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 0.43M(circle dot) and 0.39M(circle dot) for MOA-2011-BLG-090 and 0.57M(circle dot) and 0.17M(circle dot) 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.</p
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 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 chi(2) difference between the planetary and binary model is similar to 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 Delta chi(2) similar to 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.</p