19 research outputs found
Revealing Short-period Exoplanets and Brown Dwarfs in the Galactic Bulge using the Microlensing Xallarap Effect with the \textit{Nancy Grace Roman Space Telescope}
The \textit{Nancy Grace Roman Space Telescope} (\textit{ Roman}) will provide
an enormous number of microlensing light curves with much better photometric
precisions than ongoing ground-based observations. Such light curves will
enable us to observe high-order microlensing effects which have been previously
difficult to detect. In this paper, we investigate \textit{Roman}'s potential
to detect and characterize short-period planets and brown dwarfs (BDs) in
source systems using the orbital motion of source stars, the so-called xallarap
effect. We analytically estimate the measurement uncertainties of xallarap
parameters using the Fisher matrix analysis. We show that the \textit{Roman}
Galactic Exoplanet Survey (RGES) can detect warm Jupiters with masses down to
0.5 and orbital period of 30 days via the xallarap effect.
Assuming a planetary frequency function from \citet{Cumming+2008}, we find
\textit{Roman} will detect hot and warm Jupiters and close-in
BDs around microlensed source stars during the microlensing survey. These
detections are likely to be accompanied by the measurements of the companion's
masses and orbital elements, which will aid in the study of the physical
properties for close-in planet and BD populations in the Galactic bulge.Comment: Accepted for publication in The Astronomical Journa
Candidate Brown-dwarf Microlensing Events with Very Short Timescales and Small Angular Einstein Radii
Short-timescale microlensing events are likely to be produced by substellar brown dwarfs (BDs), but it is difficult to securely identify BD lenses based on only event timescales t_E because short-timescale events can also be produced by stellar lenses with high relative lens-source proper motions. In this paper, we report three strong candidate BD-lens events found from the search for lensing events not only with short timescales (t_E ≲ 6 days) but also with very small angular Einstein radii (θ_E ≲ 0.05 mas) among the events that have been found in the 2016–2019 observing seasons. These events include MOA-2017-BLG-147, MOA-2017-BLG-241, and MOA-2019-BLG-256, in which the first two events are produced by single lenses and the last event is produced by a binary lens. From the Monte Carlo simulations of Galactic events conducted with the combined t_E and θ_E constraint, it is estimated that the lens masses of the individual events are
0.051^(+0.100)_(−0.027) M⊙, 0.044^(+0.090)_(−0.023) M⊙, and 0.046^(+0.067)_(−0.023) M⊙/0.038^(+0.056)_(−0.019) M⊙ and the probability of the lens mass smaller than the lower limit of stars is ~80% for all events. We point out that routine lens mass measurements of short-timescale lensing events require survey-mode space-based observations
A Gas Giant Planet in the OGLE-2006-BLG-284L Stellar Binary System
We present the analysis of microlensing event OGLE-2006-BLG-284, which has a
lens system that consists of two stars and a gas giant planet with a mass ratio
of to the primary. The mass ratio of the
two stars is , and their projected separation is AU, while the projected separation of the planet from the primary
is AU. For this lens system to have stable orbits, the
three-dimensional separation of either the primary and secondary stars or the
planet and primary star must be much larger than that these projected
separations. Since we do not know which is the case, the system could include
either a circumbinary or a circumstellar planet. Because there is no
measurement of the microlensing parallax effect or lens system brightness, we
can only make a rough Bayesian estimate of the lens system masses and
brightness. We find host star and planet masses of , , and
, and the -band magnitude of the combined
brightness of the host stars is . The separation
between the lens and source system will be mas in mid-2020, so it
should be possible to detect the host system with follow-up adaptive optics or
Hubble Space Telescope observations
A Gas Giant Planet in the OGLE-2006-BLG-284L Stellar Binary System
We present the analysis of microlensing event OGLE-2006-BLG-284, which has a lens system that consists of two stars and a gas giant planet with a mass ratio of q_p = (1.26 ± 0.19) × 10⁻³ to the primary. The mass ratio of the two stars is q_s = 0.289 ± 0.011, and their projected separation is s_s = 2.1 ± 0.7 au, while the projected separation of the planet from the primary is s_p = 2.2 ± 0.8 au. For this lens system to have stable orbits, the three-dimensional separation of either the primary and secondary stars or the planet and primary star must be much larger than the projected separations. Since we do not know which is the case, the system could include either a circumbinary or a circumstellar planet. Because there is no measurement of the microlensing parallax effect or lens system brightness, we can only make a rough Bayesian estimate of the lens system masses and brightness. We find host star and planet masses of, M_(L1) = 0.35^(+0.30)_(−0.20) M⊙, M_(L2) = 0.10^(+0.09)_(−0.06) M⊙, and m_p = 144^(+126)_(−82) M⊕, and the K-band magnitude of the combined brightness of the host stars is K_L = 19.7^(+0.7)_(−1.0). The separation between the lens and source system will be ~90 mas in mid-2020, so it should be possible to detect the host system with follow-up adaptive optics or Hubble Space Telescope observations
Candidate Brown-dwarf Microlensing Events with Very Short Timescales and Small Angular Einstein Radii
Short-timescale microlensing events are likely to be produced by substellar brown dwarfs (BDs), but it is difficult to securely identify BD lenses based on only event timescales t_E because short-timescale events can also be produced by stellar lenses with high relative lens-source proper motions. In this paper, we report three strong candidate BD-lens events found from the search for lensing events not only with short timescales (t_E ≲ 6 days) but also with very small angular Einstein radii (θ_E ≲ 0.05 mas) among the events that have been found in the 2016–2019 observing seasons. These events include MOA-2017-BLG-147, MOA-2017-BLG-241, and MOA-2019-BLG-256, in which the first two events are produced by single lenses and the last event is produced by a binary lens. From the Monte Carlo simulations of Galactic events conducted with the combined t_E and θ_E constraint, it is estimated that the lens masses of the individual events are
0.051^(+0.100)_(−0.027) M⊙, 0.044^(+0.090)_(−0.023) M⊙, and 0.046^(+0.067)_(−0.023) M⊙/0.038^(+0.056)_(−0.019) M⊙ and the probability of the lens mass smaller than the lower limit of stars is ~80% for all events. We point out that routine lens mass measurements of short-timescale lensing events require survey-mode space-based observations
Systematic KMTNet Planetary Anomaly Search, Paper I: OGLE-2019-BLG-1053Lb, A Buried Terrestrial Planet
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 . A Bayesian
analysis yields estimates of the mass of the host star, , the mass of its planet, , the projected planet-host separation,
au, and the lens distance of 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 .Comment: published by A