We report the discovery and analysis of a planet in the microlensing event OGLE-2018-BLG-0799. The planetary signal was observed by several ground-based telescopes, and the planet-host mass ratio is ...q = (2.65 ± 0.16) × 10(−3). The ground-based observations yield a constraint on the angular Einstein radius θE, and the microlensing parallax vector πE, is strongly constrained by the Spitzer data. However, the 2019 Spitzer baseline data reveal systematics in the Spitzer photometry, so there is ambiguity in the magnitude of the parallax. In our preferred interpretation, a full Bayesian analysis using a Galactic model indicates that the planetary system is composed of an Mplanet = 0.26+0.22 −0.11M(J) planet orbiting an Mhost = 0.093+0.082 −0.038 Mʘ , at a distance of DL = 3.71+3.24 −1.70 kpc. An alternate interpretation of the data shifts the localization of the minima along the arc-shaped microlens parallax constraints. This, in turn, yields a more massive host with median mass of 0.13 Mʘ at a distance of 6.3 kpc. This analysis demonstrates the robustness of the osculating circles formalism, but shows that further investigation is needed to assess how systematics affect the specific localization of the microlens parallax vector and, consequently, the inferred physical parameters.
ABSTRACT
We report the discovery and analysis of a planet in the microlensing event OGLE-2018-BLG-0799. The planetary signal was observed by several ground-based telescopes, and the planet-host mass ...ratio is q = (2.65 ± 0.16) × 10−3. The ground-based observations yield a constraint on the angular Einstein radius θE, and the microlensing parallax vector $\boldsymbol{{\pi} }_{\rm E}$, is strongly constrained by the Spitzer data. However, the 2019 Spitzer baseline data reveal systematics in the Spitzer photometry, so there is ambiguity in the magnitude of the parallax. In our preferred interpretation, a full Bayesian analysis using a Galactic model indicates that the planetary system is composed of an $M_{\rm planet} = 0.26_{-0.11}^{+0.22}M_{\rm J}$ planet orbiting an $M_{\rm host} = 0.093_{-0.038}^{+0.082}~\mathrm{M}_{\odot }$, at a distance of $D_{\rm L} = 3.71_{-1.70}^{+3.24}$ kpc. An alternate interpretation of the data shifts the localization of the minima along the arc-shaped microlens parallax constraints. This, in turn, yields a more massive host with median mass of $0.13 {\, \mathrm{M}_{\odot }}$ at a distance of 6.3 kpc. This analysis demonstrates the robustness of the osculating circles formalism, but shows that further investigation is needed to assess how systematics affect the specific localization of the microlens parallax vector and, consequently, the inferred physical parameters.
Abstract
We report the analysis of microlensing event OGLE-2017-BLG-1038, observed by the Optical Gravitational Lensing Experiment, Korean Microlensing Telescope Network, and Spitzer telescopes. The ...event is caused by a giant source star in the Galactic Bulge passing over a large resonant binary-lens caustic. The availability of space-based data allows the full set of physical parameters to be calculated. However, there exists an eightfold degeneracy in the parallax measurement. The four best solutions correspond to very-low-mass binaries near (
M
1
=
170
−
50
+
40
M
J
and
M
2
=
110
−
30
+
20
M
J
), or well below (
M
1
=
22.5
−
0.4
+
0.7
M
J
and
M
2
=
13.3
−
0.3
+
0.4
M
J
) the boundary between stars and brown dwarfs. A conventional analysis, with scaled uncertainties for Spitzer data, implies a very-low-mass brown-dwarf binary lens at a distance of 2 kpc. Compensating for systematic Spitzer errors using a Gaussian process model suggests that a higher mass M-dwarf binary at 6 kpc is equally likely. A Bayesian comparison based on a galactic model favors the larger-mass solutions. We demonstrate how this degeneracy can be resolved within the next 10 years through infrared adaptive-optics imaging with a 40 m class telescope.
In order to exhume the buried signatures of “missing planetary caustics” in Korea Microlensing Telescope Network (KMTNet) data, we conducted a systematic anomaly search of the residuals from ...point-source point-lens fits, based on a modified version of the KMTNet Event Finder algorithm. This search revealed the lowest-mass-ratio planetary caustic to date in the microlensing event OGLE-2019-BLG-1053, for which the planetary signal had not been noticed before. The planetary system has a planet–host mass ratio ofq= (1.25±0.13) × 10−5. A Bayesian analysis yielded estimates of the mass of the host star, Mhost =-0.61+0.29 -0.24 Mo, the mass of its planet, Mplanet =-2.48 +1.19 -0.98 Mo, the projected planet – host separation, a^= 3.4 +0.5/-0.5 au, and the lens distance, DL =-6.8 +0.6 -0.90kpc.The discovery of this very-low-mass-ratio planet illustrates the utility of our method and opens a new window for a large and homogeneous sample to study the microlensing planet–host mass ratio function down to q∼ 10−5.
In this work, we present the analysis of the binary microlensing event OGLE-2018-BLG-0022 that is detected toward the Galactic bulge field. The dense and continuous coverage with the high-quality ...photometry data from ground-based observations combined with the space-based Spitzer observations of this long timescale event enables us to uniquely determine the masses M 1 = 0.40 ± 0.05 M ⊙ and M 2 = 0.13 ± 0.01 M ⊙ of the individual lens components. Because the lens-source relative parallax and the vector lens-source relative proper motion are unambiguously determined, we can likewise unambiguously predict the astrometric offset between the light centroid of the magnified images (as observed by the Gaia satellite) and the true position of the source. This prediction can be tested when the individual-epoch Gaia astrometric measurements are released.
We present the analysis of the microlensing event OGLE-2015-BLG-0845, which was affected by both the microlensing parallax and xallarap effects. The former was detected via the simultaneous ...observations from the ground and Spitzer, and the latter was caused by the orbital motion of the source star in a relatively close binary. The combination of these two effects led to a direct mass measurement of the lens object, revealing a low-mass (\(0.14 \pm 0.05 M_{\odot}\)) M-dwarf at the bulge distance (\(7.6 \pm 1.0\) kpc). The source binary consists of a late F-type subgiant and a K-type dwarf of \(\sim1.2 M_{\odot}\) and \(\sim 0.9 M_{\odot}\), respectively, and the orbital period is \(70 \pm 10\) days. OGLE-2015-BLG-0845 is the first single-lens event in which the lens mass is measured via the binarity of the source. Given the abundance of binary systems as potential microlensing sources, the xallarap effect may not be a rare phenomenon. Our work thus highlights the application of the xallarap effect in the mass determination of microlenses, and the same method can be used to identify isolated dark lenses.
We report the analysis of microlensing event OGLE-2017-BLG-1038, observed by the Optical Gravitational Lensing Experiment, Korean Microlensing Telescope Network, and Spitzer telescopes. The event is ...caused by a giant source star in the Galactic Bulge passing over a large resonant binary lens caustic. The availability of space-based data allows the full set of physical parameters to be calculated. However, there exists an eightfold degeneracy in the parallax measurement. The four best solutions correspond to very-low-mass binaries near (\(M_1 = 170^{+40}_{-50} M_J\) and \(M_2 = 110^{+20}_{-30} M_J\)), or well below (\(M_1 = 22.5^{+0.7}_{-0.4} M_J\) and \(M_2 = 13.3^{+0.4}_{-0.3} M_J\)) the boundary between stars and brown dwarfs. A conventional analysis, with scaled uncertainties for Spitzer data, implies a very-low-mass brown dwarf binary lens at a distance of 2 kpc. Compensating for systematic Spitzer errors using a Gaussian process model suggests that a higher mass M-dwarf binary at 6 kpc is equally likely. A Bayesian comparison based on a galactic model favors the larger-mass solutions. We demonstrate how this degeneracy can be resolved within the next ten years through infrared adaptive-optics imaging with a 40 m class telescope.
In order to exhume the buried signatures of "missing planetary caustics" in the KMTNet data, we conducted a systematic anomaly search to the residuals from point-source point-lens fits, based on a ...modified version of the KMTNet EventFinder algorithm. This search reveals the lowest mass-ratio planetary caustic to date in the microlensing event OGLE-2019-BLG-1053, for which the planetary signal had not been noticed before. The planetary system has a planet-host mass ratio of \(q = (1.25 \pm 0.13) \times 10^{-5}\). A Bayesian analysis yields estimates of the mass of the host star, \(M_{\rm host} = 0.61_{-0.24}^{+0.29}~M_\odot\), the mass of its planet, \(M_{\rm planet} = 2.48_{-0.98}^{+1.19}~M_{\oplus}\), the projected planet-host separation, \(a_\perp = 3.4_{-0.5}^{+0.5}\) au, and the lens distance of \(D_{\rm L} = 6.8_{-0.9}^{+0.6}\) kpc. The discovery of this very low mass-ratio planet illustrates the utility of our method and opens a new window for a large and homogeneous sample to study the microlensing planet-host mass-ratio function down to \(q \sim 10^{-5}\).
OGLE-2016-BLG-1093 is a planetary microlensing event that is part of the statistical \(Spitzer\) microlens parallax sample. The precise measurement of the microlens parallax effect for this event, ...combined with the measurement of finite source effects, leads to a direct measurement of the lens masses and system distance: \(M_{\rm host} = 0.38\)--\(0.57\, M_{\odot}\), \(m_p = 0.59\)--\(0.87\, M_{\rm Jup}\), and the system is located at the Galactic bulge (\(D_L \sim 8.1\) kpc). Because this was a high-magnification event, we are also able to empirically show that the "cheap-space parallax" concept Gould & Yee (2012) produces well-constrained (and consistent) results for \(|\pi_{\rm E}|\). This demonstrates that this concept can be extended to many two-body lenses. Finally, we briefly explore systematics in the \(Spitzer\) light curve in this event and show that their potential impact is strongly mitigated by the color-constraint.
We report the discovery and analysis of a planet in the microlensing event
OGLE-2018-BLG-0799. The planetary signal was observed by several ground-based
telescopes, and the planet-host mass ratio is ...$q = (2.65 \pm 0.16) \times
10^{-3}$. The ground-based observations yield a constraint on the angular
Einstein radius $\theta_{\rm E}$, and the microlensing parallax vector
$\vec{\pi}_{\rm E}$, is strongly constrained by the Spitzer data. However, the
2019 Spitzer baseline data reveal systematics in the Spitzer photometry, so
there is ambiguity in the magnitude of the parallax. In our preferred
interpretation, a full Bayesian analysis using a Galactic model indicates that
the planetary system is composed of an $M_{\rm planet} =
0.26_{-0.11}^{+0.22}~M_{J}$ planet orbiting an $M_{\rm host} =
0.093_{-0.038}^{+0.082}~M_{\odot}$, at a distance of $D_{\rm L} =
3.71_{-1.70}^{+3.24}$ kpc. An alternate interpretation of the data shifts the
localization of the minima along the arc-shaped microlens parallax constraints.
This, in turn, yields a more massive host with median mass of $0.13
{M_{\odot}}$ at a distance of 6.3 kpc. This analysis demonstrates the
robustness of the osculating circles formalism, but shows that further
investigation is needed to assess how systematics affect the specific
localization of the microlens parallax vector and, consequently, the inferred
physical parameters.
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